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A

PROJECT REPORT

ON

DESIGN, FABRICATION AND TESTING OF A PRESSURETRANSDUCER FOR THE CONDITION MONITORING OF THE OIL

LUBRICATION SYSTEM FOR GENERATOR SET

SUBMITED TO THE UNIVERSITY OF PUNE,

IN THE PARTIAL FULFILLMENT OF THE REQUIREMENTS

FOR THE AWARD OF THE DEGREE

OF

BACHELOR OF ENGINEERING

(MECHANICAL ENGINEERING)

SUBMITTEED BY:

SUMEET GHODKE B8310830

KEDAR LELE B8310865

RAVISH NAGARKAR B8310874

DEPARTMENT OF MECHANICAL ENGINEERING

PROGRESSIVE EDUCATION SOCIETYS

MODERN COLLEGE OF ENGINEERING, SHIVAJINAGAR,

PUNE-05.

2011-2012


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P. E. S. MODERN COLLEGE OF ENGINEERING, PUNE-05

CERTIFICATE

This is to certify that this project report entitledDesign, fabrication and testing of

a pressure transducer for the condition monitoring of the oil lubrication system

for generator setsubmitted by

Sumeet Ghodke, University Seat No: B-8310830

Kedar Lele, University Seat No: B-8310852

Ravish Nagarkar, University Seat No: B-8310864

is a partial fulfilment of BE Mechanical Engineering project work, under the

University of Pune, year 2011-2012.

Date: 16/06/2012 Place: Pune

Internal Guide Head of Department

Prof. M. M. Nadkarni Prof. Dr. A. D. Desai

Prof. Dr. Mrs. K. R. Joshi EXAMINER

Principal

PESs MCOE, Pune-5


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ACKNOWLEDGEMENT

It is with great pleasure that we present the report on our project work at the end ofthe final year. We take this opportunity to share a few words of gratitude to all those

who have supported us in making it possible. Our heartfelt gratitude to our project

guide Prof. Mr. M. M. Nadkarni for his able and expert guidance. We would also like

to thank Mr. V. S. Deshpande (M.D. Sam Integrations Pvt. Ltd.) for trusting us with

this project and providing unconditional support and guidance.

We are very thankful to Dr. Mr. Gajanan Ekbote (Chairman), Dr. Mrs. K. R. Joshi

(Principal) and Prof. Mr. A. D. Desai (Vice Principal) for their moral support and

encouragement. We are also indebted to our college including the staff members,

technical assistants of various laboratories and other non-teaching staff for providing

us with all the resources.

Place: Pune

Date: 16/06/2012


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LIST OF FIGURES

Figure 1: Tank Unit for gensets ................................................................................................ 13

Figure 2: S-series Fuel Indicator ............................................................................................... 13

Figure 3: Fuel Indicator ............................................................................................................ 13

Figure 4: Drain Pump ............................................................................................................... 13

Figure 5: Fire Safety Equipments ............................................................................................. 13

Figure 6: Fuel Filling Neck ........................................................................................................ 13

Figure 7: Oil lubrication system ............................................................................................... 16

Figure 8: Pressure gauge mounting on gen-set ....................................................................... 17

Figure 9: Assembly of RICO pressure transducer ..................................................................... 23

Figure 10: C-shaped bourdon tube .......................................................................................... 25

Figure 11: Helical bourdon tube .............................................................................................. 26

Figure 12: Spiral bourdon tube ................................................................................................ 26

Figure 13: Flat diaphragm ........................................................................................................ 27

Figure 14: Schematic diaphragm pressure gauge .................................................................... 27

Figure 15: Convoluted diaphragm ........................................................................................... 28

Figure 16: Capsule .................................................................................................................... 28

Figure 17: Set of bellow pressure gauge .................................................................................. 29

Figure 18: Single acting cylinder .............................................................................................. 29

Figure 19: U-tube manometer ................................................................................................. 30

Figure 20: Circumferential Stress ............................................................................................. 33

Figure 21: Longitudinal Stress .................................................................................................. 33

Figure 22: Von-mises stress in cylinder.................................................................................... 38Figure 23: Maximum principal stress on cylinder .................................................................... 38

Figure 24: Maximum shear stress on cylinder ......................................................................... 39

Figure 25: Total deformation on cylinder ................................................................................ 39

Figure 26: Sequence of operation for cylinder manufacturing................................................ 41

Figure 27: Cylinder ................................................................................................................... 41

Figure 28: Sequence of operation for spring manufacturing .................................................. 46

Figure 29: Spring ...................................................................................................................... 46

Figure 30: Piston with two grooves ......................................................................................... 48

Figure 31: Piston with one groove ........................................................................................... 49

Figure 32: Piston with two split ring and one O-ring ............................................................... 50

Figure 33: Teflon piston head and brass rod (Detachable) ...................................................... 51

Figure 34: Threaded teflon piston head and brass rod (detachable) ...................................... 52

Figure 35: Sequence of operation of Piston ............................................................................ 53

Figure 36: Threaded joint used ................................................................................................ 54

Figure 37: Von-mises stress on head hex ................................................................................ 55

Figure 38: Maximum principal stress on head hex .................................................................. 55

Figure 39: Maximum shear stress on head hex ....................................................................... 56

Figure 40: Total deformation on head hex .............................................................................. 56

Figure 41: Von-mises stress on end hex .................................................................................. 58
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Figure 42: Maximum principal stress on end hex .................................................................... 58

Figure 43: Maximum shear stress on end hex ......................................................................... 59

Figure 44: Total deformation on end hex ................................................................................ 59

Figure 45: Sequence of operation for hex nut manufacturing ................................................ 60

Figure 46: Basic O-Ring ............................................................................................................ 61

Figure 47: Basic Gland .............................................................................................................. 61

Figure 48: Gland and O-Ring Seal ............................................................................................ 61

Figure 49: O-Ring Installed ....................................................................................................... 62

Figure 50: O-Ring under pressure ............................................................................................ 62

Figure 51: O-Ring Extruding ..................................................................................................... 63

Figure 52: O-Ring Under Extrusion Failure .............................................................................. 63

Figure 53: Abrasion .................................................................................................................. 63

Figure 54: Compression Set ..................................................................................................... 64

Figure 55: Chemical degradation ............................................................................................. 65

Figure 56: Explosive Decompression ....................................................................................... 65Figure 57: Extrusion ................................................................................................................. 66

Figure 58: Installation Damage ................................................................................................ 66

Figure 59: Outgassing/Extaction .............................................................................................. 67

Figure 60: Overcompression .................................................................................................... 67

Figure 61: Plasma Degradation ................................................................................................ 68

Figure 62: Spiral Failure ........................................................................................................... 69

Figure 63: Thermal Degradation .............................................................................................. 69

Figure 64: O-Ring ..................................................................................................................... 76

Figure 65: Friction due to O-ring compression ........................................................................ 78

Figure 66: Friction due to fluid pressure .................................................................................. 78

Figure 67: Variation in Pressure Force (Fp), Friction Force (Fc) with Cylinder ID .................... 79

Figure 68: Protective cover for pressure transducer ............................................................... 81

Figure 69: Principal of linear potentiometer ........................................................................... 82

Figure 70: Principal of LVDT ..................................................................................................... 84

Figure 71: Bonded resistance strain gauge .............................................................................. 85

Figure 72: Variable area capacitors ......................................................................................... 87

Figure 73: Test rig suggested ................................................................................................... 89

Figure 74: Pressure Vs Displacement Graph for 8mm ID cylinder ........................................... 94

Figure 75: Pressure Vs Displacement Graph for 10mm ID cylinder ......................................... 97


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LIST OF TABLES

Table 1: SAM Customers .......................................................................................................... 12

Table 2: Oil for different temperature ranges ......................................................................... 14

Table 3: Design selection chart ................................................................................................ 31

Table 4: Cylinder Thickness for 8mm ID Cylinder .................................................................... 35

Table 5: Selected thickness for 8 mm ID cylinder .................................................................... 36

Table 6: Cylinder Thickness for 10mm ID Cylinder .................................................................. 36

Table 7: Selected thickness for 10 mm ID cylinder .................................................................. 36

Table 8: Stresses on cylinder by ANSYS ................................................................................... 40

Table 9: Spring calculations ..................................................................................................... 44

Table 10: Spring Manufactured ............................................................................................... 45

Table 11: Stresses on head hex by ANSYS ............................................................................... 57

Table 12: Stresses on end hex by ANSYS ................................................................................. 60

Table 13: Abressive Failure contributing factors and Suggested solutions ............................. 64

Table 14: Compression set failure Contributing factors and Suggested solutions .................. 64

Table 15: Chemical degradation failure Contributing factors and Suggested solutions ......... 65

Table 16: Explosive decompression failure Contributing factors and Suggested solutions .... 65

Table 17: Extrusion Failure contributing factors and Suggested solutions.............................. 66

Table 18: Installation Damage contributing factors and Suggested solutions ........................ 67

Table 19: Outgassing/ Extraction failure Contributing factors and Suggested solutions ........ 67

Table 20: Overcompression Failure contributing factors and Suggested solutions ................ 68

Table 21: Plasma Degradation contributing factors and Suggested solutions ........................ 68

Table 22: Spiral Failure contributing factors and Suggested solutions .................................... 69Table 23: Thermal degradation failure contributing factors and Suggested solutions ........... 70

Table 24: Stick slip- Possible causes and troubleshooting tips ................................................ 70

Table 25: O-Ring Compression ................................................................................................. 72

Table 26: Recommended Maximum Compression for O-Ring ................................................ 73

Table 27: Comparison of dynamic seal type ............................................................................ 74

Table 28: Comparison of commonly used materials for O-Rings ............................................ 75

Table 29: Important parameters for friction determination ................................................... 77

Table 30: Determined values for friction determination ......................................................... 79

Table 31: Values from graph .................................................................................................... 79

Table 32: Total available force for piston movement .............................................................. 80

Table 33: Observation Table for 8mm ID cylinder in reverse direction ................................... 92

Table 34: Observation Table for 8mm ID cylinder in reverse direction ................................... 93

Table 35: Observation Table for 10mm ID cylinder in forward direction ................................ 96

Table 36: Observation Table for 10mm ID cylinder in reverse direction ................................. 97

Table 37: FMECA Chart for Manufactured Pressure Transducer ........................................... 102
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TABLE OF CONTENT

CERTIFICATE ....................................................................................................................................... 1

ACKNOWLEDGEMENT ........................................................................................................................ 2

LIST OF FIGURES ................................................................................................................................. 3

LIST OF TABLES ................................................................................................................................... 5

TABLE OF CONTENT ............................................................................................................................ 6

SYMBOLS USED .................................................................................................................................. 8

1. ABSTRACT ................................................................................................................................ 10

2. COMPANY PROFILE .................................................................................................................. 11

3. OBJECTIVE OF THE PROJECT ..................................................................................................... 14

4. NEW PRODUCT DEVELOPMENT AND ITS NEED ........................................................................ 15

5. INTRODUCTION: THE SYSTEM .................................................................................................. 16

6. STEPS OF PROJECT WORK ........................................................................................................ 18

7. BACKGROUND: ........................................................................................................................ 19

HOW OIL CONDITION MONITORING OCCURS? ................................................................................. 19

8. MARKET SURVEY ..................................................................................................................... 22

9. PRESSURE MEASUREMENT MECHANISMS IN BRIEF ................................................................. 25

10. MAJOR COMPONENTS OF THE SINGLE ACTING CYLINDER FOR TRANSDUCER ...................... 32

11. CYLINDER ............................................................................................................................. 33

12. SPRING ................................................................................................................................ 42

12. PISTON ................................................................................................................................ 47

13. JOINT USED .......................................................................................................................... 54

14. O RING............................................................................................................................... 61

15. PREDICTING SEAL FRICTION ................................................................................................. 77

16. PROTECTIVE COVER ............................................................................................................. 81

17. MEASUREMENT OF LINEAR DISPLACEMENT ........................................................................ 82

18. TESTING OF THE PRESSURE TRANSDUCER............................................................................ 88

19. COSTING .............................................................................................................................. 98

20. MAINTENANCE OF THE PRESSURE TRANSDUCER ................................................................. 99

21. FAILURE MODE, EFFECT AND CRITICALITY ANALYSIS ......................................................... 100

22. SWOT ANALYSIS ................................................................................................................ 104

23. FUTURE SCOPE .................................................................................................................. 106

24. CONCLUSIONS ................................................................................................................... 108


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25. REFERENCES ...................................................................................................................... 109

ANNEXTURE-I: MATLAB PROGRAM FOR GRAPH GENERATION .................................................. 110

ANNEXTURE-II: SHENDE SALES CORPORATION CATALOGUE FOR O RINGS ............................. 111


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SYMBOLSUSED

T -torque

Di -cylinder inner diameter

t -cylinder thickness

t -hoop stress

l -longitudinal stress

r -radial stress

-poisons ratio

-allowable shear stress

p -pressure inside the cylinder

Syt -tensile yield strength

Sper -permissible tensile stress

Ss -permissible shear stress

G -modulus of rigidity

c -spring index

D -mean coil diameter of spring

d -wire diameter

Kw -wahls factor

N -number of spring turns

Nt -total number of spring turns

Lw -working length of spring

Lc -clearance allowance for spring

Li -initial compression of spring

Lf -free length of spring

Ps -pitch of spring


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F -load acting on spring

S -stretch value for O-Ring

Gd -O-Ring groove diameter

Srec -recommended stretch value for O-Ring

ID -inner diameter for O-Ring

Bd -bore diameter

CS -cross section diameter of O-Ring

C -compression of O-Ring

GW -groove width

F -total friction force

FC -friction force due to seal squeeze

FH -friction force due to pressure

fC -friction factor for seal squeeze

fH -friction factor for pressure

Lh -piston circumference

Ar -seal projected area

RPN -risk priority number

S -severity

O -occurrence

D -detection


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1. ABSTRACT

Condition monitoring service gives an ongoing program of sampling, analysis and

reporting of the system under observation. It provides the information you need to

pin-point and solve equipment problems as well as implement a more effective

maintenance system. In condition monitoring of oil lubrication system, there are

various parameters to be analysed, pressure being the most important one. This

pressure when continuously monitored, gives an idea about the health of the

lubrication system. This confirms the importance of pressure gauges in condition

monitoring of oil lubrication system.

The main intention of the project is to design a pressure transducer to give the

pressure readings for the condition monitoring of a lubrication system of a generator

set. This objective is persuaded with design theory, ANSYS, manufacturing processes

with a great fruit of success.


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2. COMPANY PROFILEA. History:

Having started the business under the banner of Ideas Toolings, SAM holds over 17

years of experience in this industry. Later in the year 2004, it merged as SAM

Integrations Private Limited and have established as one of the premier manufacturers

and exporters of a comprehensive range of Electro Mechanical Products.

B. Directors:Chairman: Mr. V. S. Deshpande

M. Des., IIT, Bombay.

Having more than 27 years of hands on experience

Managing Director: Mr. N. B. Tembe

B. Tech., Specialisation in production.

Having more than 32 years of hands on experience.

C. Basic Information of company:Business Type:

Manufacturer

Exporter

Ownership & Capital:

Year of Establishment- 2004

Ownership Type- Private Limited Company

Certification & Membership:

Certification Name- ISO 9001:2008

Start Date- 26-APR-11

Expiry Date: 11-JUN-14


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D. Customers:

E. Team & Staff: Total Number of Employees-51 to 100 People

F. Application Areas:The Electro Mechanical Products designed in the unit are evaluated for maximum

durability, ability to withstand wear & tear and accurate performance. These features

make SAMs products compatible to withstand most severe applications and

environments. The product range offers solutions to the following areas:

Generator

Compressor

Escalators

Automotives

Diesel Engines

Other Industrial Applications

R.T.S. Inc., MI 49015, USA Fike Safety Technology Ltd, United Kingdom

Kirloskar Brothers Limited Shirwal Kirloskar Engines India Ltd.

Jakson Enterprises Silvassa Ashok Leyland LimitedMahindra & Mahindra Ltd. Powerica Ltd Silvassa, Banglore, Taloja

Cummins India Ltd Greaves Cotton Limited

Premier Engineering Works Sterling Generators Pvt. Ltd.

Nasan Medicals Jeevan Diesels & Electricals Ltd.

Standard Meter Mfg. Co. Mahalasa Acoustic Pvt. Ltd.

Shamraj Engineering Power Engineering (I) Pvt. Ltd.

Philip Harris UK Maya Engineering

Core Objects Sunbeam Generators Pvt. Ltd.

Table 1: SAM Customers


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G. PRODUCT RANGE AT SAMTank Units for Gensets

Figure 1: Tank Unit for gensets

S-Series Fuel Indicator

Figure 2: S-series Fuel Indicator

Fuel Indicator

Figure 3: Fuel Indicator

Drain Pump

Figure 4: Drain Pump

Fire Safety Equipments

Figure 5: Fire Safety Equipments

Fuel Filling Neck

Figure 6: Fuel Filling Neck

(Reference# 1)


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3. OBJECTIVE OF THE PROJECTThe pressure transducers used in generator sets for condition monitoring of

lubrication system in the current industrial scenario consist of a diaphragm

mechanism which gives minimum deflection with respect to the pressure, to measure

this deflection to calibrate the pressure; we need some arm effect to get good range of

output. This arm effect does add some rounding-off errors, which leads to unreliable

output from the transducer, where transducer is a device which convert the parameter

to be measured into a proportional electrical quantity which can be directly read using

an indicator. So to overcome this error in readings it is required to look for some more

appropriate mechanism which will lead to less errors or at least avoid some

complications in the current designs followed by the industry.

A.Technical specification to be attained: Pressure range: 0-5 bar

Output deflection required: 15mm for 5 bar

Accuracy expected: +/- 5%

Temperature: 70C max

Engine oil viscosity: Use an oil having viscosity best suited to the atmosphericconditions. Use of an all season SAE 10W/30 having low viscosity change

with change in temperature is suggested.

Temperature (C) Viscosity

68F (20C) or higher SAE 30 or SAE10W/30

41F (5C) to 68F (20C) SAE 20 or SAE10W/20

Below 41F SAE 20

Table 2: Oil for different temperature ranges

(NOTE: Do not use an engine lubricating oil with a SAE rating number above 30 in

the engine.)

So the prime objective of the project is to design such a pressure transducer which

satisfies the technical specifications, minimizes the errors found in current industrial

design and redesign the product.

(Reference# 1)


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4. NEW PRODUCT DEVELOPMENT AND ITS NEEDNew product development is a vital part of any business. It doesn't matter whether the

product is for consumers or other businesses, whether it is a tangible object or a

service. The constant change in markets and technology require that companies take

steps to meet new challenges. Developing new products and improving existing

products is an important step in meeting this challenge. New product development can

be just what it sounds like the creation of a completely new product that fills a

previously unaddressed niche in the economy. Product development also includes re-

examining an existing product to maximize its market potential through adding

features, a design change or maybe just tweaking the marketing.

Fortunately, product innovation is not a completely hit or miss proposition. There are

steps a company can take to improve the likelihood of a successful development

process. There is no one "best" method for developing products, and what works for

one segment of a particular industry may not work for another industry, or maybe not

even for another segment of that industry. The mix of elements will be different for

every product development project, but companies can look to a basic framework to

help keep all the different elements on track.

The goal of the product development process is to end up with the best possible

product. One that is well suited for the intended audience and contains features that is

needed and desired. No matter how great the new product may seem, if the market

rejects it, it's a failure. Taking the product development process seriously can go a

long way toward making the end result a success.


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5. INTRODUCTION: THE SYSTEMIn the system, the oil is forced under pressure through the oil line by a pump. In the

oil line it passes through the filter and then to the manifold. The manifold supplies the

oil to the main lubrication system and various components requiring oil. One oil line

is passed to the pressure gauge which measures the pressure in the oil line produced

by the pump.

Looking at the schematic, many factors come into play when setting oil pressure.

Each of the manifold outputs is designed for certain volume, and the individual

calculated circuit resistances come into play to determine overall resistance to oil

flow. This is much like having four or five hoses connected to one hose bib on the

side of the house if one bursts, all will lose pressure. If one is plugged up, the pressure

increases for the rest. This system is much the same. So if an output is clogged, like

the governor line for instance, pressure will rise. If your transmission has worn out

main bearings allowing much of the oil to slide back into the crankcase prematurely,

pressure will be lower. The bottom line here is that any rather sudden rise or fall in oil

pressure should be taken as a signal that your engines oiling system needs attention.

This way pressure gauge plays an important role oil lubrication system.

(Reference# 17)

Figure 7: Oil lubrication system


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PRESSURE GAUGE MOUNTING ON GEN-SET

Figure 8: Pressure gauge mounting on gen-set


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6. STEPS OF PROJECT WORK Market survey

Analyzing available market products

Brain storming for all possible concepts of pressure transducers

Studying for best workable concept

Drawing the basic structure of the pressure transducer

Optimizing the design with dimensions, material, joining processes, surface

finish, etc.

Manufacturing the prototype of the product

Testing the product and reviewing design

Working on the steps of aesthetics, durability, safety, recyclability, ease of use,

etc.

Finalizing the design with optimum parameters


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7. BACKGROUND:How oil condition monitoring occurs?

An oil condition monitoring service gives you an ongoing program of sampling,

analysis and reporting. It provides the information you need to pinpoint and solve

equipment problems as well as implement a more effective maintenance system.

Lubricating oils contain all the requisite additives to protect the equipment from wear,

corrosion and excess friction. The additives in the oil are multi-functional, therefore,

it is important they do not deplete (and is one of the reasons oil types should not be

mixed). This is particularly important in long term usage.

A. Types of oil condition monitoring:1. On-line testing

2. Off-line testing

Visual darkening of oil

A burnt smell to the oil

An increase in viscosity

Visual haziness

Foaming

It is important that oil condition monitoring is completed on a regular basis to ensure

that the oil quality is stable. Regular monitoring soon builds a history of the fluid

condition allowing informed decisions to be taken.

Continued operation with degraded oil will lead to accelerated wear of moving parts

and filtration problems resulting in an accumulation of sludge in the tank and pipe-

work.

B. Conventional analysis makes use of oil sampling techniqueswhich suffer from some serious drawbacks:

1. It takes to process the sample; machinery can be damaged from poor lubricant

quality.

2. Secondly, one can never be sure that the oil sampled is representative of the entire

lubricating system. Various sampling techniques are used in an attempt to acquire

the best sample, but there are still possibilities that the sample collected is not the

most representative of the system.


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3. When a sample is taken, it is difficult to ensure no outside contamination from the

sampling procedure, container or laboratory has been introduced.

4. Finally, off-line oil sampling and analysis can be costly.

Real time monitoring is a vital tool, which can allow lubricants to be used to their

fullest potential while minimizing machinery downtime, resulting in increased savings

and productivity. Real time sensors provide the ability to conduct continuous

monitoring. This is beneficial on many levels, especially in responding to suddenly

occurring faults and condition trending.

C. On-line oil condition monitoringOil is forced under pressure through the oil line by a pump. Filtered oil is then forced

through oil lines to the manifold. The manifold supplies the oil to the main lubrication

system and various components requiring oil. One oil line from manifold is passed to

the pressure gauge which measures the pressure in the oil line produced by the pump.

An oil pressure gauge gives an excellent indication of the health of various systems in

the engine. The key is to establish baseline readings when the engine is healthy, and

then be aware of any changes over the time.

D. Cause of low pressure: The contaminant in oil line and mostly in the filter block the flow of oil in the

system which tends to reduce the pressure at which the is to be supplied to the

engine and other parts.

Low oil level

Damaged oil pan or pick-up tube

High Oil Temperature- Generally not a big factor, but if you're pulling a trailer or

running flat out in really hot weather, your oil can run well over 250F., and oil

pressure will be lower.

Worn Oil Pump - This could be anything from a slight reduction all the way to

catastrophic failure (which is rare unless the pump has ingested bits of metal from

some other failure).


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E. Cause of high pressure:High oil pressure is not generally a concern, but if pressure suddenly increases, there

may be a problem with the pressure relief valve. Switching to higher viscosity oil will

also show higher readings.

(Reference# 17)


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8. MARKET SURVEYThe project started with a search for all available and possible mechanisms for the

particular objective of condition monitoring of lubrication system ie. pressure gauge.

Starting with internet, we found many makers of such pressure transducers with

different principles been utilized some of which are also used for automobiles

application.

A. COMPETITOR MANUFACTURER Pricol

RICO

Saudamini

VDO

B. RICO COMPONENT ANALYSISADVANTAGES

Robust construction

Small in size

Ease of mounting

DRAWBACKS

Hystersis due to torsional spring

Not precisely and accurate

Assembly not easy to repair

Less life due to use of diaphragm

(Reference# 14, 18)


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Figure 9: Assembly of RICO pressure transducer


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C. DIFFERENT MECHANISMS FOR PRESSUREMEASUREMENT

Mechanical

1. Bourdon tube

a. C-shaped bourdon tube

b. Helical bourdon tube

c. Spiral bourdon tube

2. Diaphragm

a. Flat diaphragm

b. Convoluted diaphragm

c. Capsule

3. Set of bellow

4. Single acting cylinder

5. Manometer

Electrical

1. Capacitive type.

2. Strain gauge.

3. Piezo-electric type.

As the requirement is for the mechanical type pressure transducer, hence electrical

types of pressure measuring elements are neglected.

(Reference# 2, 4, 6, 8)


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9. PRESSURE MEASUREMENT MECHANISMS IN BRIEFA. Bourdon tube:

i.

C-shaped bourdon tube:

Eugene Bourdon invented this type of gauge in 1851. He stated that round tubing

which has been flattened and bent into a circular arc will tend to return to its original

shape when a pressure is applied inside it. The operation is similar to that of the paper

coiled-tube blowers used at parties. In its simplest form it consists of a length of thin-

walled metal tubing which has been flattened, to approximately an elliptical cross

section and then rolled into a C shape, having an arc span of about 270.

Figure 10: C-shaped bourdon tube

The external pressure is guided into the tube and causes it to flex, resulting in a

change in curvature of the tube. These curvature changes are linked to the dial

indicator for a number readout.


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ii. Helical bourdon tube:

Figure 11: Helical bourdon tubeHelical bourdon tube pressure gauge sensing element is formed inthe helical spring

shape. The distance of the bourdon tube from the center tube is very much more than

the C-Type. The sensitivity of this type is more due to its angular length.

When input pressure is applied, pointer will rotate along with its axis and pointer end

showing reading on a scale which is marked in pressure units. It converts pressure to

displacement; in this type of bourdon tube no additional gain mechanism is required.

iii. Spiral bourdon tube:

Figure 12: Spiral bourdon tube

The radius of the tube from the centre is continuously vary in figure it increasing. The

inner end of the tube is treated as reference and outer free end gives the displacement

according to applied pressure.If a pointer is attached to the outer free end of the tube,


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then it directly gives the pressure measurement on a scale which is marked in pressure

units.In some designs the free end of the Bourdon is wound round several times with

the socket-pressure connection at the centre. Figure 13 shows the general idea of such

an element. The amount of movement varies directly with the angle subtended by the

total arc. By increasing the number of turns in the spiral or helix, a greater movement

of the tip is obtained.

B. Diaphragm :i. Flat diaphragm:

Figure 13: Flat diaphragm

The flat diaphragm pressure gauge uses the elastic deformation of a diaphragm (i.e.

membrane) instead of a liquid level to measure the difference between an unknown

pressure and a reference pressure.

A typical Diaphragm pressure gage contains a capsule divided by a diaphragm, as

shown in the schematic below. One side of the diaphragm is open to the external

targeted pressure, PExt, and the other side is connected to a known pressure, PRef. The

pressure difference, PExt - PRef, mechanically deflects the diaphragm.

Figure 14: Schematic diaphragm pressure gauge


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ii. Convoluted diaphragm:

Figure 15: Convoluted diaphragm

The working principle is just the same as the flat diaphragm only the construction is

different.

iii. Capsule:A capsule is formed by joining the peripheries of two diaphragms through soldering

or welding.

Figure 16: Capsule


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C. The set of bellow:

Figure 17: Set of bellow pressure gauge

Bellow type pressure gauges use a spring loaded elastic material bellow to measure

the pressure and the indication is with linkages.

D. Single acting cylinder:Piston cylinder type is utilized in this kind of pressure gauge assembly, where on one

side of piston there is the application of pressure and on the other side a counter

weight is applied which also measures the deflection, hence giving pressure reading.

Figure 18: Single acting cylinder


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E. Manometer:Manometers are working on the principle of hydrostatic balancing. The force acting

due to one liquid column on the same level or reference balances the force acting due

to another liquid column. The simplest manometer consists of a tube made of glass orother transparent material bent into the shape of a U and with both ends left open. A

few spoonfuls of water poured into the tube is all that is required to make a

manometer. The liquid-filled manometer is one of the most useful and inherently

accurate instruments for measuring any variable that is a function of pressure.

Because of its simplicity and accuracy the manometer is widely used.

Figure 19: U-tube manometer

(Reference# 2, 4, 6, 8)


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F. DESIGN SELECTIONParameter

Bourdontube

Diaphra

gm

Setofbellow

Single

acting

cylinder

Manom

eter

Ease of manufacturing

Ease of assembly

Ease of calibration

Design strength

Output accuracy

Product reliability

Long product durability

Low product cost

Table 3: Design selection chart

INFERENCE

Single acting cylinder assembly has the most no. of checks, which indicates that it has

the most no. of desired properties with this mechanism. For this particular application

of condition monitoring of lubrication system the output is required for the change in

pressure not for accurate readings, hence the single acting cylinder mechanism is bestsuited for the application of pressure measurement.


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10. MAJOR COMPONENTS OF THE SINGLE ACTINGCYLINDER FOR TRANSDUCER

1. Cylinder Design

2. Helical Compression Spring Design

3. Piston Design

4. Joint Used

5. O Ring Selection

6. Protective Cover

7. Electronic System and Pointer Arrangement

These are the major components of the single acting cylinder assembly for thepressure transducer. Designing for strength, manufacturing, assembly, aesthetics and

environmental impact completes the primary design of pressure transducer.


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11. CYLINDERA. DESIGN OF CYLINDER

i. INTRODUCTIONDepending upon whether the cylinder wall thickness is appreciable or not, in relation

to the inner diameter of the cylinder, the cylinder are classified into two categories:

1. Thin cylinder (Di/t>20)

2. Thick cylinder (Di/t


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The magnitude of the radial stress is equal to the internal pressure at the inner surface

of the cylinder and zero at the outer surface of the cylinder.

As the cylinder is subjected to three principal stresses, different theories of failure are

used in the design of the cylinder subjected to internal pressure. The selection of the

theory depends upon two parameters:

i. Cylinder material (whether brittle or ductile)

ii. Condition of cylinder ends (open or closed)

iii. Different theories of failures used in the design of the cylinders subjected tointernal pressure are

1.

Maximum principal stress theory (Lames theory)

Used when the cylinder is made of brittle material like cast iron.

2. Maximum principal strain theory

Cylinder with closed end (Clavarinos theory)

Cylinder with open end (Birnies theory)

3. Maximum shear stress theory

Used when the cylinder is made of ductile material like MS, brass etc.

4. Distortion energy theory

As the cylinder for the particular application is to be made with ductile material,

the theories used are

A. Maximum principal strain theory (Clavarinos theory)

B. Maximum principal strain theory (Birnies theory)

C. Maximum shear stress theory

D. Distortion energy theory

iv. Formulae Used:A. Maximum principal strain theory (Clavarinos theory)

t=[[()() ] ]


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B. Maximum principal strain theory (Birnies theory)

t=[[()() ] ]

C. Maximum shear stress theoryt=[[ ] ]

D. Distortion energy theory

t=[[ ] ]

(Reference# 3, 9, 10, 12, 13)

The following table contains specifications for three categories namely plastics,

metals, and glass-fibers. Specifications have been calculated for the given set of

values:

v. SET-11. Pressure=P = 5 bar = 0.5 N/mm

2

2. Dia. Of Piston=Di= 8 mm

3. Factor of safety= 4

The cylinder is provided with a threading at both ends hence forming a critical

thickness at that section.

Thread used:

M121.25

material syt per.

stress

(sper)

per. shear

stress

(ss)

thickness by

clavarinos

theory

thickness by

birnies

theory

thickness by

maximum

shear stress

theory

thickness by

distortion

energy

theory

(MPa) (MPa) (MPa) (mm) (mm) (mm) (mm)

Steel 480 120 60 0.014218550 0.016722480 0.016771562 0.014512351

Brass 200 50 25 0.034300754 0.040323599 0.040610178 0.035097611

Table 4: Cylinder Thickness for 8mm ID Cylinder


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The thickness allowance for the threads t=0.77mm

Total thickness required= t+safe value of thickness from chart

Material Total thickness required (mm) Approximated thickness (mm)

Steel 0.77+0.01677=0.78677 2

Brass 0.77+0.04061=0.81061 2

Table 5: Selected thickness for 8 mm ID cylinder

(with considering the manufacturing limitation the thickness is assumed as 2mm)

vi. SET-21. Pressure=P = 5 bar = 0.5 N/mm

2

2. Dia. Of Piston=Di= 10 mm

3. Factor of safety= 4

Table 6: Cylinder Thickness for 10mm ID Cylinder

The cylinder is provided with a threading at both ends hence forming a critical

thickness at that section.

Thread used:

M141.5

The thickness allowance for the threads t=1.08mm

Total thickness required= t+safe value of thickness from chart

Material Total thickness required (mm) Approximated thickness (mm)

Steel 1.08+0.02096=1.10096 2

Brass 1.08+0.05076=1.13076 2

Table 7: Selected thickness for 10 mm ID cylinder

(with considering the manufacturing limitation the thickness is assumed as 2mm)

material syt per.

stress

(sper)

per. shear

stress

(ss)

thickness by

clavarinos

theory

thickness by

birnies

theory

thickness by

maximum

shear stress

theory

thickness by

distortion

energy

theory

(MPa) (MPa) (MPa) (mm) (mm) (mm) (mm)

Steel 480 120 60 0.017773187 0.020903101 0.020964452 0.018140443

Brass 200 50 25 0.042875942 0.050404499 0.050762722 0.043872014


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vii. INFERENCE1. With the consideration of material availability, ease of manufacturing and the

critical thickness required for brass and M.S., they are selected for the prototype

design purpose.2. Not knowing the critical diameter for least friction between O-ring and cylinder

the two diameters 8mm and 10mm are selected for analysis.


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B. ANSYS REPORT FOR CYLINDERSTRUCTURAL ANALYSIS (Mat- Brass)

i. VON-MISES STRESS

Figure 22: Von-mises stress in cylinder

ii. MAXIMUM PRINCIPLE STRESS

Figure 23: Maximum principal stress on cylinder


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iii. MAXIMUM SHEAR SHTRESS

Figure 24: Maximum shear stress on cylinder

iv. TOTAL DEFORMATION

Figure 25: Total deformation on cylinder


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v. INFERENCEType

Equivalent (von-

Mises) Stress

Maximum

Principal Stress

Maximum

Shear Stress

Total

Deformation

Minimum 1.1252e-003 MPa -1.1213 MPa5.6626e-004

MPa0. mm

Maximum 1.6202 MPa 0.28252 MPa 0.88713 MPa 3.0369e-005 mm

Table 8: Stresses on cylinder by ANSYS

With reference to allowable stress on brass (50 MPa), the maximum stress developed

in cylinder (1.6202 MPa) from ANSYS, the cylinder is safe.


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C. MANUFACTURING OF THE CYLINDERMachines used: Lathe m/c, grinding m/c

Operations performed: Turning, drilling, boring, threading, chamfering, grinding

Sequence of operation:

Figure 26: Sequence of operation for cylinder manufacturing

Figure 27: Cylinder

RAW MATERIAL CUTTING

FACING

TURNING

DRILLING

FINISH

REAMING

THREADING

START


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12. SPRINGi. DESIGN OF SPRINGi. INTRODUCTION

The design of a new spring involves the following considerations:

ii. Space into which the spring must fit and operate.

iii. Values of working forces and deflections.

iv. Accuracy and reliability needed.

v. Tolerances and permissible variations in specifications.

vi. Environmental conditions such as temperature, presence of a corrosive

atmosphere.vii. Cost and qualities needed.

The designers use these factors to select a material and specify suitable values for the

wire size, the number of turns, the coil diameter and the free length, type of ends and

the spring rate needed to satisfy working force deflection requirements. The primary

design constraints are that the wire size should be commercially available and that the

stress at the solid length be no longer greater than the torsional yield strength. Further

functioning of the spring should be stable.

Springs are fundamental mechanical components which form the basis of many

mechanical systems. A spring can be defined to be an elastic member that exerts a

resisting force when its shape is changed. Most springs are assumed linear and obey

the Hooke's Law.

ii. SPRING MATERIALThe most extensively used spring material is high-carbon hard drawn spring steel. It is

often called Patented and cold-drawn steel wire. This material has been used for

most spring manufacturing due to its good response to spring requirements and hence

it is selected for the particular spring design.

iii. SPRING CHARACTRISTICS End style- Square and ground end

Right handed spring


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Spring material- Unalloyed, oil hardened and tempered spring steel valve spring

wire (VW)

Expected deflection- 22.5mm for 7.5 bar pressure

iv. FORMULAE AND DATA USED FOR DESIGN1.Modulus of rigidity (G) = 83170 N/2.Spring Index (C) =

3.Wahls Factor () = ()() 4.Number of Turns (N) =

5.Total number of turns ( ) = N + 26.Working Length () =

7.Solid Length () = * d8.Clearance Allowance () = 15% of working length9.Total Length (

) +

10. Pitch (Ps) =

11. Shear Stress ( ) =

(Reference# 9, 10, 11, 12, 15)

v. SPRING HYSTERSISHysteresis is the loss of mechanical energy under cyclic loading and unloading of a

spring. It results from frictional losses in the spring support system due to tendency of

the ends to rotate as the spring is compressed. Hysteresis for compression springs is

low and the contribution due to internal friction in the spring material itself is

generally negligible.


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vi. INFERENCEThe highlighted spring designs are selected for the manufacturing purpose on the

basis of its ease of manufacturing and dimensional limitations.

Table 9: Spring calculations


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vi. MANUFACTURING OF THE SPRINGThe spring is not manufactured in the firm, so it was order from the Bhalchand

Spring Pvt. Ltd.

The material available were stainless steel, M.S. and spring steel. The spring is the

recommended one by the manufacturer and design data book, hence we preferred the

spring steel for the application.

Dimensions of the springs manufactured:

Parameter Spring 1 Spring 2

Mean spring diameter 5.8 mm 8 mm

Inner diameter 5 mm 7 mm

Outer diameter 6.6 mm 9 mm

Pitch 3 mm 4.5 mm

Total no. of turns 15 10

Wire diameter 0.8 mm 1 mm

Free length 42 mm 40.5 mm

Material Spring steel Spring steel

Type of end Square and ground end Square and ground end

Spring hand Right handed Right handed

Table 10: Spring Manufactured


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SEQUENCE OF PROCESS

Figure 28: Sequence of operation for spring manufacturing

Figure 29: Spring


Stainless Steel / S rin Steel

SIZING

COLD WINDING

GRINDING

FINISH

START

STRESS RELIVING IN A FURNACE


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12. PISTONA. PISTON DESIGN

i. INTRODUCTIONThe function of piston is to take pressure of oil on one side and on the other side the

spring force. As the stresses acting on the piston are very small compared to the piston

strength hence the piston is not designed on strength basis. The more important

aspects are mass of piston, no. of groves, piston end design, pointer attachment at the

end of the piston rod, buckling reaction of spring on the piston rod.

Factors considered in piston design:

Mass of the piston: The mass of the piston primarily depend upon the material of

the piston. M.S., brass, aluminum, delrin and Teflon are the materials which were

available for manufacturing. As the application is in the oil the M.S. is prone to

rust hence it is eliminated. Brass has been used for hydraulic cylinders hence it

was of prime focus, but the density of brass is quiet high. Aluminum was quiet

likely material for the application but the availability has been the problem.

Delrin and Teflon were rejected based on its buckling tendency ie strength basis

as the rod is likely to experience a buckling from the spring buckling as it is

supposed to act as a guide for the spring. Hence brass is selected for the

manufacturing.

No. of groves: While testing on single grooved piston, it was observed that there

was quite a lot of play at the end of piston, so double grooved piston is preferred.

Pointer attachment: There have been many possibilities for pointer attachments

but the threaded joint is chosen for its ease of handling for primary testing

purpose.

Piston rod diameter: The piston rod is supposed to be as thin as possible but the

manufacturing problems constraints the size of the piston rod to 4mm. Hence

4mm rod is preferred.

Groove width: Groove width for O-ring attachment is kept a bit more than the

O-ring diameter so as to allow play for O-ring between the grooves, so as to

avoid crushing stresses.


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ii. DIFFERENT PISTON DESIGNS TRIEDa) PISTON WITH TWO GROOVES

Figure 30: Piston with two grooves

Characteristics

No leakage observed

Robust construction

Two O-rings helps in avoiding oscillation of piston


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b)PISTON WITH ONE GROOVE

Figure 31: Piston with one groove

Characteristics

Leakage was observed after 3.2 bar pressure

Robust construction

One O-ring doesnt make it fully leakage proof

One support allows piston to oscillate


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c) PISTON WITH TWO SPLIT RING AND ONE O-RING

Figure 32: Piston with two split ring and one O-ring

Characteristics


Robust construction

O-ring gives positive sealing


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d)TEFLON PISTON HEAD AND BRASS ROD (DETACHABLE)

Figure 33: Teflon piston head and brass rod (Detachable)

Characteristics


Kinematic constraints are utilised for improving manufacturing

No positive sealing

With lack of precise manufacturing process the piston was prone to leakage


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B. MANUFACTURING OF PISTONThe piston is manufactured on a lathe machine, so the primary drawback that came to

the product was the accuracy of the dimensions. The piston is manufactured with

brass as it was available at SAM. The threading at the end of piston for pointer

attachment is made of M3 as it was the least tap available.

SEQUENCE OF OPERATION

Figure 35: Sequence of operation of Piston


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13. JOINT USEDA. INTRODUCTION

Currently the market trend is to make the product such that it wont be possible to

open the assembly and repair or get the mechanism behind the joints. As the product

is in the design phase we assumed the threaded joints to be most appropriate for the

primary design.

While thinking about the product to be manufactured we assumed plastic welding to

be the most appropriate joining process, as the whole component is to be

manufactured from plastic for the mass production.

Figure 36: Threaded joint used


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B. ANSYS REPORT FOR HEAD HEXi. VON MISES STRESS

Figure 37: Von-mises stress on head hex

ii. MAXIMUM PRINCIPAL STRESS

Figure 38: Maximum principal stress on head hex


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iii. MAXIMUM SHEAR STRESS

Figure 39: Maximum shear stress on head hex


Figure 40: Total deformation on head hex


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v. INFERENCE

TypeEquivalent (von-

Mises) Stress

Maximum

Principal Stress

Maximum Shear

Stress

Total

Deformation

Minimum 6.5967e-007 MPa -1.2119 MPa 3.5209e-007 MPa 0. mm


Table 11: Stresses on head hex by ANSYS




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C. ANSYS REPORT FOR END HEXi. VON MISES STRESS

Figure 41: Von-mises stress on end hex

ii. MAXIMUM PRINCIPAL STRESS

Figure 42: Maximum principal stress on end hex


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iii. MAXIMUM SHEAR STRESS

Figure 43: Maximum shear stress on end hex


Figure 44: Total deformation on end hex


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v. INFERENCE

TypeEquivalent (von-

Mises) Stress

Maximum

Principal Stress

Maximum Shear

Stress

Total

Deformation

Minimum 1.1977e-005 MPa -1.4534 MPa 6.8174e-006 MPa 0. mm


Table 12: Stresses on end hex by ANSYS



D. SEQUENCE OF OPERATION

Figure 45: Sequence of operation for hex nut manufacturing

START


Brass

DRILLING

BORING

TAPING

FINISH

THREADING


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14. O RINGA. INTRODUCTION

An O-ring seal is used to prevent the loss of a fluid or gas. The seal assembly consists

of an elastomer O-ring and a gland. An O-ring is a circular cross-section ring moulded

from rubber.

Figure 46: Basic O-Ring

Figure 47: Basic Gland

Figure 48: Gland and O-Ring Seal

i. Advantages of O-Rings seals:a) They seal over a wide range of pressure, temperature and tolerance.

b) Ease of service, no smearing or retightening.

c) No critical torque on tightening, therefore unlikely to cause structural damage.

d) O-rings normally require very little room and are light in weight.

e) Where differing amounts of compression effects the seal function, an O-ring is

not affected because metal to metal contact is generally allowed for.

f) They are cost-effective.


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ii. O-RING INSTALLATIONThe rubber seal should be considered as essentially an incompressible, viscous fluid

having a very high surface tension. Whether by mechanical pressure from the

surrounding structure or by pressure transmitted through hydraulic fluid, this

extremely viscous fluid is forced to flow within the gland to produce zero clearance

or block to the flow of the less viscous fluid being sealed.

The rubber absorbs the stack-up of tolerances of the unit and its internal memory

maintains the sealed condition. Figure illustrates the O-ring as installed, before the

application of pressure. Note that the O-ring is mechanically squeezed out of round

between the outer and inner members to close the fluid passage.

Figure 49: O-Ring Installed

iii.

VARIOUS STAGES O-RING UNDER APPLICATION OFMECHANICAL PRESSURE

STAGE I- PRESSURE APPLIED

The seal material under mechanical pressure extrudes into the micro-fine grooves of

the gland. Figure illustrates the application of fluid pressure on the O-ring. Note that

the O-ring has been forced to flow up to, but not into, the narrow gapbetween the

mating surfaces and in so doing, has gained greater area and force of sealing contact.

Figure 50: O-Ring under pressure


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STAGE IIPRESSURE LIMIT REACHED

Figure shows the O-ring at its pressure limit with a small portion of the seal material

entering the narrow gap between inner and outer members of the gland.

Figure 51: O-Ring Extruding

STAGE IIIEXTRUSION FAILURE

Figure illustrates the result of further increasing pressure and the resulting extrusion

failure. The surface tension of the elastomer is no longer sufficient to resist flow and

the material extrudes (flows) into the open passage or clearance gap.

Figure 52: O-Ring Under Extrusion Failure

iv. COMMON MODES OF FAILUREa) ABRASION

Figure 53: Abrasion


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Description:

The seal or parts of the seal exhibit a flat surface parallel to the direction or motion.

Loose particles and scrapes may be found on the seal surface.

Contributing Factors Suggested Solutions

a. Rough sealing surfaces.

b. Excessive temperature.

c. Process environment containing

abrasive particles.

d. Dynamic motion.

e. Poor elastomer surface finish.

a. Use recommended gland surface

finishes.

b. Consider internally lubed elastomers.

c. Eliminate abrasive components.

Table 13: Abressive Failure contributing factors and Suggested solutions

b) COMPRESSION SET

Figure 54: Compression Set

Description: The seal exhibits a flat-sided cross-section, the flat sides correspoding to

the mating seal surfaces.


a. Excessive compression.

b. Excessive temperature.

c. Incompletely cured elastomer.

d. Elastomer with high compression set.

e. Excessive volume swell in chemical.

a. Low compression set elastomer.

b. Proper gland design for the specific

elastomer.

c. Confirm material compatibility.

Table 14: Compression set failure Contributing factors and Suggested solutions


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c) CHEMICAL DEGRADATION

Figure 55: Chemical degradation

Description:

The seal may exhibit many signs of degradation including blisters, cracks, voids or

discoloration. In some cases, the degradation is observable only by measurement of

physical properties.


Incompatibility with the chemical and/or

thermal environment.

Selection of more chemically resistant

elastomer.

Table 15: Chemical degradation failure Contributing factors and Suggested solutions

d) EXPLOSIVE DECOMPRESSION

Figure 56: Explosive Decompression

Description:

The seal exhibits blisters, pits or pocks on its surface. Absorption of gas at high

pressure and the subsequent rapid decrease in pressure. The absorbed gas blisters and

ruptures the elastomer surface as the pressure is rapidly removed.


a. Rapid pressure changes.

b. Low-modulus/hardness elastomer.

a. Higher-modulus/hardness elastomer.

b. Slower decompression.

Table 16: Explosive decompression failure Contributing factors and Suggested solutions


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e) EXTRUSION

Figure 57: Extrusion

Description: The seal develops ragged edges (generally on the low-pressure side)

which appear tattered.


a. Excessive clearances.

b. Excessive pressure.

c. Low-modulus/hardness elastomer.

d. Excessive gland fill.

e. Irregular clearance gaps.

f. Sharp gland edges.

g. Improper sizing.

a. Decrease clearances.

b. Higher-modulus/hard-ness elastomer.

c. Proper gland design.

d. Use of polymer backup rings.

Table 17: Extrusion Failure contributing factors and Suggested solutions

f) INSTALLATION DAMAGE

Figure 58: Installation Damage

Description:

The seal or parts of the seal may exhibit small cuts, nicks or gashes.


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a. Sharp edges on glands or

components.

b. Improper sizing of elastomer.


d. Elastomer surface contamination.

a. Remove all sharp edges.

b. Proper gland design.

c. Proper elastomer sizing.

d. Higher-modulus/hardness elastomer.

Table 18: Installation Damage contributing factors and Suggested solutions

g) OUTGASSING / EXTRACTION

Figure 59: Outgassing/Extaction

Description:

This failure is often very difficult to detect from examination of the seal. The seal may

exhibit a decrease in cross-sectional size.


a. Improper or improperly cured

elastomer.

b. High vacuum levels.

c. Low hardness/plasticized elastomer.

a. Avoid plasticized elastomers.

b. Ensure all seals are properly post-

cured to minimize outgassing.

Table 19: Outgassing/ Extraction failure Contributing factors and Suggested solutions

h) OVERCOMPRESSION

Figure 60: Overcompression


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Description:

The seal exhibits parallel flat surfaces (corresponding to the contact areas) and may

develop circumferential splits within the flattened surfaces.


Improper designfailure to account for

thermal or chemical volume changes, or

excessive compression.

Gland design should take into account

material responses to chemical and

thermal environments.

Table 20: Overcompression Failure contributing factors and Suggested solutions

i) PLASMA DEGRADATION

Figure 61: Plasma Degradation

Description:

The seal often exhibits discoloration, as well as powdered residue on the surface and

possible erosion of elastomer in the exposed areas.


a. Chemical reactivity of the plasma.

b. Ion bombardment (sputtering).

c. Electron bombardment (heating).

d. Improper gland design.

e. Incompatible seal material.

a. Plasma-compatible elastomer and

compound.

b. Minimize exposed area.

c. Examine gland design.

Table 21: Plasma Degradation contributing factors and Suggested solutions


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j) SPIRAL FAILURE

Figure 62: Spiral Failure

Description:

The seal exhibits cuts or marks which spiral around its circumference.

Contributing Factors Suggested Solutionsa. Difficult or tight installation (static).

b. Slow reciprocating speed.


d. Irregular O-ring surface finish

(including excessive parting line).

e. Excessive gland width.

f. Irregular or rough gland surface

finish.

g. Inadequate lubrication.

a. Correct installation procedures.

b. Higher-modulus elastomer.

c. Internally-lubed elastomers.

d. Proper gland design.

e. Possible use of polymer backup

rings.

Table 22: Spiral Failure contributing factors and Suggested solutions

k) THERMAL DEGRADATION

Figure 63: Thermal Degradation


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Description:

The seal may exhibit radial cracks located on the highest temperature surfaces. In

addition, certain elastomers may exhibit signs of softeninga shiny surface as a

result of excessive temperatures.


a. Elastomer thermal properties.

b. Excessive temperature excursions or

cycling.

a. Selection of an elastomer with

improved thermal stability.

b. Evaluation of the possibility of

cooling sealing surfaces.

Table 23: Thermal degradation failure contributing factors and Suggested solutions

v. STICK SLIPStick-slip is characterized by distinct stop-start movement of the cylinder, and may be

so rapid that it resembles severe vibration, high pitched noise or chatter. Seals are

often thought to be the source of the stick-slip, but other components or hardware can

create this issue.

Possible Causes Troubleshooting Tips

Surface finish out of

specification

Verify surface is neither too smooth or too rough

Poor fluid lubricity Change fluid or use oil treatments or friction reducers

Binding wear rings Check gland dimensions, check for thermal or chemical swell

Side loading Review cylinder alignment, incorporate adequate bearing

area

Seal friction Use material with lower coefficient of friction

Cycle speed Slow movement increases likelihood of stick-slip

Temperature High temperature softens seals, expands wear rings, and can

cause thermal expansion differences within hardware

Valve pulsation Ensure valves are properly sized and adjusted

External hardware Review system for harmonic resonance

Table 24: Stick slip- Possible causes and troubleshooting tips


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vi. O-RING FAILURE ANALYSISPrevention of seal failures through proper design, material selection and maintenance

certainly minimizes the risk of failure. Attention to the condition of replaced seals, as

well as the equipment performance over time, will result in improved process

reliability, reduced operating costs and a safer work environment.

O-ring seals often fail prematurely in applications because of improper design or

compound selection. This section is designed to provide the user with examples of

common failure modes. By correctly identifying the failure mode, changes in the

design or seal material can lead to improved seal performance.

From the end-users point of view, a seal can fail in three (3) general ways:

Leaking

Contamination

Change in Appearance

vii. ENVIRONMENTAL ANALYSISOne major factor in possible seal failure is the extreme and harsh environment in

which seals are expected to perform. The sealing environment can consist of virtually

anything from inert gases at room temperatures to aggressive chemicals at very high

temperatures. The sealing environment may result in chemical degradation or

swelling of the sealing components. Elevated temperatures may cause seal

degradation, swelling or outgassing. And the pressure or more often, the vacuum

environments can cause outgassing and weight loss.

Contributing factors to seal failure in the sealing environment include:

Chemicalthe type of chemical(s) in serviceThermalthe operating ranges of the seal (also any thermal cycling)

Pressure/Vacuumthe range of pressures or vacuum levels in the process

viii. SEAL DESIGN ANALYSISAnalysis of the seal application is crucial to the understanding of possible failure.

Most seal design is performed by component suppliers and equipment manufacturers.


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The seal design and application can provide information about the cause of failure:

Static Sealsaxial and radial, confined or unconfined

Dynamic Sealsaxial (open-close) or radial (reciprocating or rotary)

Sealing Gland Dimensionsshape (square, trapezoidal, etc.), compression, gland fill,

stretch

Installation Proceduresstretch

ix. DESIGN GUIDELINES FOR RADIAL SEALSIn radial seals, the gland is defined by the Bore Diameter on the outside radius, the

Groove Diameter on the inside radius and the Groove Width in the axial direction (see

schematic).

a) INNER DIAMETERIn order for the O-Ring to fit snugly in the groove, it is desirable to circumferentially

stretch the O-Ring slightly. The recommended amount of stretch Sis between 1% to

5% , with 2% as the preferred stretch value.

The O-Ring inner diameter ID can be found from the recommended Srec and the

Groove Diameter Gd,

By stretching the O-Ring, we ensure that the O-Ring will stay in the groove and will

not fall out or otherwise twist in some unpredictable manner during assembly.

b) CROSS SECTION DIAMETERThe O-Ring is compressed in the radial direction when seated in the gland. Hence,

one can think of the O-Ring cross-section as being pinched between the Bore

Table 25: O-Ring Compression


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DiameterBdand the Groove Diameter Gd. In order for the ORing to be compressed

when in the gland, its cross-section diameter CS must be greater than the total

effective depth of the groove,

The difference between CSand the effective gland depth represents the compression

Cof the O-Ring (a dimensionless quantity),

C is required to be greater than zero in order for the O-Ring to be compressed. The

recommended upper limit ofCdepends on the type of seal. In static seals, where the

O-Ring is not in axial motion in the bore, the recommended maximum compression is

approximately 40%. In dynamic seals, such as a piston moving inside a cylinder, the

recommended maximum compression is somewhat less at 30%.

Table 26: Recommended Maximum Compression for O-Ring

Typically, compression is a design input assigned by the design engineer. In this case,

CS is found by inverting the above compression equation,


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To account for manufacturing tolerances, a range of cross-section diameters (CSmin

to CSmax) can be provided by the following two equations,

c) GROOVE WIDTHWhen the O-Ring is compressed radially, it will expand axially (since most

elastomeric materials are effectively incompressible). The Groove Width GW should

therefore be about 1.5 times the O-Ring cross-section diameter to accomodate this

axial expansion,

x. Comparison of dynamic seal types:Type

Periodic

adjustment

required

Moving

friction

Tolerance

required

Space

sequiredAvailability Cost

O-ring No Medium Close Small Easy Low

T-seal No MediumFairly

closeSmall Difficult High

U-packing No Low Close Small Difficult High

V-packing Yes MediumFairly

closeLarge Difficult High

Cup type

packingNo Medium Close Medium Difficult High

Table 27: Comparison of dynamic seal type

The comparison chart gives clear indication that O-rings and U-packing are the most

suitable ones for the application but with availability and cost giving advantage to O-

rings, hence O-rings are selected.


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xi. Comparison of commonly used materials for O-rings:(P=Poor, F=Fair, G=Good, E=Exelent)

Elastomer type

Abrasiveresistance

Acidresistance

Chemicalresistance

Coldresistance

Dynamicproperty

Electricalproperty

Flameresistance

Heatresistance

Impermiability

Oilresistance

Tearresistance

Tensilestrength

Weatherresistance

Butadiene E FG FG G F G P F F P GE E F

Butyl FG G E G F G P G E P G G GE

Chlorinated polyethylene G F FG PF G G GE G G FG FG G E

Flurocarbon G E E PF GE F E E G E F GE E

Flurosilicon P FG E GE P E G E P G P F E

Isoprene E FG FG G F G P F F P GE E F

Natural rubber E FG FG G E G P F F P GE E F

Neoprene G FG FG FG F F G G G FG FG G E

Nitrile G G FG G GE F P G G E FG GE F

Polysulfide P P P G F F P P E E P F E

Silicon P FG GE E P E F E P FG P P E

Table 28: Comparison of commonly used materials for O-Rings

Taking into consideration the different properties required for the particular

application, cost and availability, silicon and nitrile are selected. While testing on both

the material O-rings, it was observed that nitrile gives more resistance for the piston

movement inside the cylinder compared to the one with silicon O-ring. Hence Silicon

O-ring is selected for the application.

(Reference# 5, 16)


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Selection of dimensions of O-ring:

Selection criteria:

The O-ring diameter should be least possible so as to touch the least area and give

least friction.

The mean diameter of the O-ring should be less than the grove outer diameter.

The excessive O-ring diameter should be 10% of the O-ring diameter.

The grove provided should be wider than the O-ring diameter, so as to provide

some pl