Upload
mohammed-al-odat
View
225
Download
0
Embed Size (px)
Citation preview
7/28/2019 Industrial Hydraulic Systems
1/58
6/18/2013Welcome to the World of Fluid Power1
Industrial Hydraulic Systems
7/28/2019 Industrial Hydraulic Systems
2/58
6/18/2013Welcome to the World of Fluid Power2
Introduction
Hydraulics is a part of Fluid Power &Motion Control
Hydraulic Systems are robust, accurate,user friendly but complicated
Keeping the Hydraulic Systems inrestoration is only possible through
knowledge and skill.
7/28/2019 Industrial Hydraulic Systems
3/58
6/18/2013Welcome to the World of Fluid Power3
Agenda
We will be covering the basic threeaspects namelyEnergy Input, Energy
Control & Energy Output. We will learn about all the three aspects as
mentioned above through explanation ofPrinciples involved in hydraulic controltechnology using colored pens & whiteboard.
7/28/2019 Industrial Hydraulic Systems
4/58
6/18/2013Welcome to the World of Fluid Power4
Programme Objectives
To understand basic principles of Hydraulics. To learn & understand the hydraulic graphic
symbols.
To understand Hydrodynamic & Hydrostatic
Pumps.
To understand & learn about hydraulic controlvalve technology.
To understand hydraulic Loads & their application To learn how to analyze hydraulic circuits.
To understand & grasp the methods of HydraulicSystem Troubleshooting & Condition Monitoring.
7/28/2019 Industrial Hydraulic Systems
5/58
6/18/2013Welcome to the World of Fluid Power5
Vocabulary
We will be working with the following terms -Q - Flow Rate
P - System Pressure
F - Force
A - Effective Area
V - Volume
v - Velocity
P - Pressure DifferentialT - Temperature Differential
7/28/2019 Industrial Hydraulic Systems
6/58
6/18/2013Welcome to the World of Fluid Power6
Vocabulary
F
A P
Relationship between Force
(lbsf), Pressure (psi) and
Area (in2
)
Relationship between Pump
Volume (GPM), Velocity
(in/Sec) and Cylinder Area(in2)
Q
v A
7/28/2019 Industrial Hydraulic Systems
7/586/18/2013Welcome to the World of Fluid Power7
Flow & Flow Rate
1. Open Channel Flow
2. Confined Flow
Why Flow takes place
Flow takes place from higher region to lower region
Flow takes place from higher pressure to lower pressure
Flow through any restriction is a function ofpressure drop across it (P).
7/28/2019 Industrial Hydraulic Systems
8/586/18/2013Welcome to the World of Fluid Power
8
Open Channel Flow
If a river is flowing from a higher level to lower levelthen flow is taking place in an open area.
Flowing (falling)
water can cause awheel to rotate, open
channel hydraulic
energy is converted
into mechanical
energy
Flowing (falling) water can
cause a wheel to rotate,
open channel hydraulic
energy isconverted into
mechanical energy
7/28/2019 Industrial Hydraulic Systems
9/586/18/2013Welcome to the World of Fluid Power
9
Flow Through Pipes
We have seen that it is possible to convert energy inthe flowing water into Mechanical energy.
The reverse is also possiblewhich means that
Mechanical energy can be converted into flowingWater (Hydraulic energy)
But before we understand how it is possible to make the
Water (liquid) to flow from lower level to higher level,
let us understand few basic principles ------------
7/28/2019 Industrial Hydraulic Systems
10/586/18/2013Welcome to the World of Fluid Power
10
Flow through a pipe can be in two states, namely
Laminar Flow & Turbulent Flow
If fluid particles are moving in parallel lines then it is
said to be Laminar flow
If the fluid particles are moving in a random path then itis said to be a Turbulent flow
Laminar Flow Turbulent Flow
Flow ConditionsLaminar Flow & Turbulent Flow
Flow Graph
7/28/2019 Industrial Hydraulic Systems
11/586/18/2013Welcome to the World of Fluid Power
11
Kinetic Energy & Potential Energy
Kinetic Energy:
Kinetic Energy is in the form of Fluid velocity & Fluid weight.
Potential Energy:
Potential energy is available in the form of Pressure
Bernoullis Theorem:
V2 P
2 +
gh+ =
Constant
where:v= fluid velocity along the streamline
g= acceleration due to gravity
h = height of the fluid
p = pressure along the streamline
= density of the fluid
http://encyclopedia.thefreedictionary.com/velocityhttp://encyclopedia.thefreedictionary.com/g-forcehttp://encyclopedia.thefreedictionary.com/heighthttp://encyclopedia.thefreedictionary.com/pressurehttp://encyclopedia.thefreedictionary.com/densityhttp://encyclopedia.thefreedictionary.com/densityhttp://encyclopedia.thefreedictionary.com/pressurehttp://encyclopedia.thefreedictionary.com/heighthttp://encyclopedia.thefreedictionary.com/g-forcehttp://encyclopedia.thefreedictionary.com/velocity7/28/2019 Industrial Hydraulic Systems
12/586/18/2013Welcome to the World of Fluid Power
12
Equation of continuity
Fluid dynamics explains that acontinuity equationis an
equation of conservation of mass
What comes in same goes out -
The law of conservation of mass/matter, also known as law of
mass/matter conservation, states that the mass of a closed system,
will remain constant, regardless of the processes acting inside the
system. An equivalent statement is that matter cannot be
created/destroyed, although it may be rearranged.
7/28/2019 Industrial Hydraulic Systems
13/586/18/2013Welcome to the World of Fluid Power
13
What is Pressure?Mathematically explained pressure is force per unit
Area, it is measured either in Lbs/in2 or Kg/cm2 but why
Pressure is created & what causes the pressure to rise?
Whenever free flow is not allowed then smallest entities try to
escape by force and in this process pressure is created if the
number of entities are large in number & every one is applying
force, pressure tend to rise
7/28/2019 Industrial Hydraulic Systems
14/58
6/18/2013Welcome to the World of Fluid Power14
What is Atmospheric Pressure?
The Planet Earth
where we live is
surrounded by a
bubble of Air, which
is spreading up to 30
mile all around
30 milesThe air particles are having weight
and due to gravitational force thisbecomes force, this force at sea level
is around 14.7 lbs/in2 (PSI) or 1.013
Kg/cm2 (BAR)
This pressure on the surface of Earthis known as Atmospheric Pressure.
How to measure any increasing or decreasing pressure on earth?
For the measurement of quantities we need a Zero reference but sinceon Earth we live under atmospheric pressure we are not having a Zero
reference. Beyond the limits of earth's atmosphere there is no air thus
there in no pressure, so no air is our reference, that is Absolute zero.
7/28/2019 Industrial Hydraulic Systems
15/58
6/18/2013Welcome to the World of Fluid Power15
Two Measuring Scales are existing
1. Absolute scale
2. Relative scale
Relative Scale Absolute Scale
0 Absolute
Gauge pressure 0
Vacuum Scale
7/28/2019 Industrial Hydraulic Systems
16/58
6/18/2013Welcome to the World of Fluid Power16
Hydraulic Pumps
1. Hydrodynamic
2. Hydrostatic
Hydrodynamic Pump:
Hydrodynamic Pumps are Non-positive displacement pumps, thesepumps provide continuous flow and there application is only limited
to fluid transfer.
Hydrostatic Pumps:
Hydrostatic Pumps are Positive displacement pumps, these pumps
provide pulsetic flow and their application is basically in the area of
Hydraulic Systems
7/28/2019 Industrial Hydraulic Systems
17/58
6/18/2013Welcome to the World of Fluid Power17
Hydrodynamic Pumps
Atmospheric Pressure
14.7 psi or 1.013 Bar
Volute Path Path
Hydrodynamic Pump:
A Centrifugal Pump falls under
the category of Hydrodynamic,
this pump provides flow by
virtue of its own construction,
if we carefully observe the
casing is volute in itsconstruction and this is the
reason that Velocity Head gets
converted into Pressure Head
at its outlet.These pumps are basically
Transfer Pumps and provide
continuous flow.
7/28/2019 Industrial Hydraulic Systems
18/58
6/18/2013Welcome to the World of Fluid Power18
Hydrostatic Pumps
500 RPM
Swept Volume of Cylinder = 10 cm3
Hydrostatic Pumps are positive displacement pumps, these
pumps are pulsetic in nature.Positive displacement pumps are used in Hydraulic Systems
Pump Size = Cubic Centimeter per Minute
Or Cubic Inches per Minute
LPM =
GPM =
CCR X RPM
1000
CIR X RPM
231
7/28/2019 Industrial Hydraulic Systems
19/58
6/18/2013Welcome to the World of Fluid Power19
Pump Specifications
Pump Type
Pump Rated Pressure
Pump Size
Pump RPM
Pump Volumetric Efficiency
Pump Mechanical Efficiency
Pump Overall Efficiency
7/28/2019 Industrial Hydraulic Systems
20/58
6/18/2013Welcome to the World of Fluid Power20
Types of PumpsPositive Displacement Pumps
Gear Pumps Vane Pumps Piston Pumps
External Gear Pump Internal Gear Pumps
Spur Gear Type Internal Gear Mesh
Lobe Type Gerator Pump
Screw Pumps
Balanced Unbalanced
Vane Pump Vane Pump
Axial Piston Radial Piston
Pumps Pumps
Axial Inline
Bent Axis
Fixed Displacement Pumps Variable Displacement pumps
7/28/2019 Industrial Hydraulic Systems
21/58
6/18/2013Welcome to the World of Fluid Power21
External Gear Pump
A Gear pump uses the meshing of
gears to pump fluid by displacement.
They are one of the most common
types ofpumps for hydraulic fluid
power applications.
There are two main variations;
external gear pumpswhich use two
external spur gears, and internal gear
pumpswhich use an external and an
internal spur gear.
Gear pumps are f ixed displacement, meaning they pump a constant
amount of fluid for each revolution.
http://encyclopedia.thefreedictionary.com/pumphttp://encyclopedia.thefreedictionary.com/hydraulic+machineryhttp://encyclopedia.thefreedictionary.com/hydraulic+machineryhttp://encyclopedia.thefreedictionary.com/gearhttp://encyclopedia.thefreedictionary.com/gearhttp://encyclopedia.thefreedictionary.com/hydraulic+machineryhttp://encyclopedia.thefreedictionary.com/hydraulic+machineryhttp://encyclopedia.thefreedictionary.com/pump7/28/2019 Industrial Hydraulic Systems
22/58
6/18/2013Welcome to the World of Fluid Power22
Internal Gear Pumps
Internal gear (Gerotor) pump design for automotive oil
pumps.
Internal gear (Gerotor) pump design for automotive oil
pumps.
A Gerotor is a positive displacement pumping unit. The
name gerotor is derived from "Generated Rotor". A Gerotor
unit consists of an inner and outer rotor.
http://encyclopedia.thefreedictionary.com/Gerotorhttp://encyclopedia.thefreedictionary.com/internal+combustion+enginehttp://encyclopedia.thefreedictionary.com/Gerotorhttp://encyclopedia.thefreedictionary.com/internal+combustion+enginehttp://encyclopedia.thefreedictionary.com/Rotor+(turbine)http://encyclopedia.thefreedictionary.com/Rotor+(turbine)http://encyclopedia.thefreedictionary.com/internal+combustion+enginehttp://encyclopedia.thefreedictionary.com/Gerotorhttp://encyclopedia.thefreedictionary.com/internal+combustion+enginehttp://encyclopedia.thefreedictionary.com/Gerotor7/28/2019 Industrial Hydraulic Systems
23/58
6/18/2013Welcome to the World of Fluid Power23
Axial Inline Piston Pump
Axial Piston Pumps are variable displacement pumps.
The pistons in an axial piston pump reciprocate parallel to the
centerline of the drive shaft of the piston block. That is, rotary shaftmotion is converted into axial reciprocating motion. Most axial
piston pumps are multi-piston and use check valves or port plates to
direct liquid flow from inlet to discharge.
Axial Piston Pumps can be
variable displacement and
pressure compensated to
match their Power with therequired Load power
7/28/2019 Industrial Hydraulic Systems
24/58
6/18/2013Welcome to the World of Fluid Power24
Pump CharacteristicsPump Rated Pressure
It is that load pressure up to which a pump can handle the loadand beyond which there is a possibility that the pump might fail.
Pump Size
Pump Size is always given in CIR/CCR or LPM/GPM.
Pump RPM
Pump RPM is always given by the Manufacturer and it normally
lies between 1250 to 1850 until & unless it is specified.
Pump Volumetric Efficiency
Volumetric efficiency is obtained by dividing Actual flow rate by
the Theoretical flow rate
7/28/2019 Industrial Hydraulic Systems
25/58
6/18/2013Welcome to the World of Fluid Power25
Pump Mechanical Efficiency
Pump Overall Efficiency
Mechanical efficiency is obtained by dividing Actual Torque by
the Theoretical Torque.
Torque in (lbs inch) =Pressure in psi X CIR (cubic inches per revolution)
2
Overall Efficiency = Volumetric Eff. x Mechanical E
ff
=Output Horse Power
Input Horse PowerX 100
7/28/2019 Industrial Hydraulic Systems
26/58
6/18/2013Welcome to the World of Fluid Power26
Pump Horse Power
Let us define Horse Power: Rate of doing work
If we explain rate of doing work we will have to go to First Principle -
Distance tobemoved 1
foot in
1 Second550lbs
1 Horse Power = 550 ft lbs/sec (This is the basic value of 1 HP)In other words we can define it in the following form
Horse Power = Force x Distance Moved per Unit time
B i H d li Ci it
7/28/2019 Industrial Hydraulic Systems
27/58
6/18/2013Welcome to the World of Fluid Power27
Basic Hydraulic Circuit
Effective Area
Load
Annulus Area
What is Working Pressure?
What is Max. System Pressure?
M1
2
3
7/28/2019 Industrial Hydraulic Systems
28/58
6/18/2013Welcome to the World of Fluid Power28
Hydraulic Graphic Symbols
A Firm & thick line is called Working Energy Line
A long dash line is known as Control Energy Line orPilot Line
A short dash line is known as Leak Line orDrain Line
Circles Triangle Filled Triangle Not Filled
Circles are used for Ball Triangles are used for Hydraulic Energy
Puppet, Energy Source, Flow Direction and Pneumatic Energy
Pump Body Flow Direction
Flow Envelop Flow Path Varying Parameter Spring Varying
Spring Force
Fluid Conditioner Thermometer Compensation Bi-directional Flow
7/28/2019 Industrial Hydraulic Systems
29/58
6/18/2013Welcome to the World of Fluid Power29
Pressure Control ValvesPressure Control Valves are very important elements in any Hydraulic
Circuit, without these valves we cant achieve correct pressure control in
different areas of control, following is a list of different types of PressureControl Valves
1. Pressure Relief Valve 5. Charge Valve
2. Pressure Reducing Valve 6. Brake Valve3. Sequence Valve 7. Unloading Valve
4. Counter Balance Valve 8. Crossover Relief Valve
THREE Types of pressure control valves are available from Technologypoint of view.
1. Spool Types 2. Simple Poppet Types
3. Cartridge Types
7/28/2019 Industrial Hydraulic Systems
30/58
6/18/2013Welcome to the World of Fluid Power30
Hydraulic Control Valves
Hydraulic Control Valves are developed over a long period of time in
two directions and categories
1. Spool Valves
2. Poppet Valves
Spool Valves provide Multiple Flow Paths, they are Pressure Balanced
but they leak between Housing and the Spool.
Poppet Valves provide Single Flow Path, They are digital in nature but
they provide Leak Proof conditions.
Both of theses categories are having advantages and disadvantages but
combined together they solve many problems.
P R li f V l
7/28/2019 Industrial Hydraulic Systems
31/58
6/18/2013Welcome to the World of Fluid Power31
Pressure Relief Valves
Pressure Relief Valves are of three Types
1. Directly Operated Pressure Relief Valve
2. Pilot Operated Pressure Relief Valve
3. Pump Unloading Valve
4. Pilot Operated Pressure Relief Cum Unloading Valve
Basic Features of Pressure Relief Valve
Normally Closed
Pressure is sensed internally at inlet port
Variable Pressure Control
Internally Drained
7/28/2019 Industrial Hydraulic Systems
32/58
6/18/2013Welcome to the World of Fluid Power32
Directly Operated Pressure Relief Valve
Directly Operated Pressure Relief valves are quick acting in nature
but these valves suffer from a drawback of large Pressure Override.These valves work alright with small volumetric flow Pumps but
these valves can not be used with large volumetric flow Pumps.
Unloading Valve
7/28/2019 Industrial Hydraulic Systems
33/58
6/18/2013Welcome to the World of Fluid Power33
Unloading Valve
While hydraulic system is
in idling condition then
Relief Valve is opening &closing to keep the system
pressure at relief valve
setting but in this process
the pump energy is usedand this is a loss, which is
converted to thermal
energy, which can cause
the oil temperature to rise
but by using an Unloadingvalve this situation can be
avoided.
Pilot Operated Pressure Relief Valve
7/28/2019 Industrial Hydraulic Systems
34/58
6/18/2013Welcome to the World of Fluid Power34
Pilot Operated Pressure Relief Valve
Directly operated pressure relief valves can only be used with 25 LPM
pumps and not beyond. For higher LPM pumps Pilot Operated pressurerelief valves are used.
Main Valve
Pilot Valve
Pilot Operated Pressure Relief cum Unloading Valve
7/28/2019 Industrial Hydraulic Systems
35/58
6/18/2013Welcome to the World of Fluid Power35
Pilot Operated Pressure Relief cum Unloading Valve
It is important to note that a separate Unloading valve will be a real
nuisance for the circuit designer more over it is essential to interface
the mechanical hardware with digital systems, so a single valve is
developed to take care of all the needs.
A Pilot Operated Pressure Relief cum Unloading valve is the most
important valve in the modern Hydraulic Systems.
Main Valve
Pilot Valve
Pressure Reducing Valve
7/28/2019 Industrial Hydraulic Systems
36/58
6/18/2013Welcome to the World of Fluid Power 36
Pressure Reducing ValvePressure Reducing Valves are also important hydraulic elements
which are used to control the pressure as per the requirement in a
branch circuit
Features of Pressure Reducing Valve
Normally Open
Pressure sensed internally at
outlet port
Variable Pressure Control Externally drained
Externally Drained
P S V l
7/28/2019 Industrial Hydraulic Systems
37/58
6/18/2013Welcome to the World of Fluid Power 37
Pressure Sequence Valve
Externally Drained
Hydraulic Pressure Sequencing
Valves are also very important
elements, since pressure sensing
control is quite accurate Designer
may consider to use a Pressure
Sequencing valve in the Hydraulic
circuit.
B k V l
7/28/2019 Industrial Hydraulic Systems
38/58
6/18/2013Welcome to the World of Fluid Power 38
Brake Valve
Brake Valve is used to stop a
single direction Hydromotor
instantly without increasing
excessive pressure and also
protecting motors fromcavitation.
These valves are very
effective and easy to adjust
for all kind of Loads.
Hydraulic Loads
7/28/2019 Industrial Hydraulic Systems
39/58
6/18/2013Welcome to the World of Fluid Power 39
Hydraulic Loads
There are three types of Hydraulic Loads
1. Resistive Loads
2. Overrunning Loads
3. Inertial Loads
Load
Hydraulic Force Load ReactionResistive Load
When Load reaction is
opposite to Hydraulic
Force then it is calledresistive load.
O i L d
7/28/2019 Industrial Hydraulic Systems
40/58
6/18/2013Welcome to the World of Fluid Power 40
Hydraulic Force Load Reaction
Overrunning Load
Load
When Load Reaction is in the same direction as that of the Hydraulic
Force then it is called Overrunning Load
Counter Balance Valve
7/28/2019 Industrial Hydraulic Systems
41/58
6/18/2013Welcome to the World of Fluid Power 41
Counter Balance Valve
Hydraulic Force Load Reaction
Counter Balance Valve is a
hydraulic control elementwhich is required to handle
heavy loads which are moved
down wards, this valve
provide support to bring theload down very smoothly and
at a required velocity to get
good control over load inertia
and acceleration due to
gravitation (g).
Counter Balance Valve
7/28/2019 Industrial Hydraulic Systems
42/58
6/18/2013Welcome to the World of Fluid Power 42
Inertial Load
When load is accelerating ordecelerating under both of these
conditions load reaction opposes the
Hydraulic force then it is called
Inertial Load.
While a Hydraulic Motor is rotating
a heavy load in both directions then
the motor is handling Inertial Load,
the motor requires protectivecircuits.
Cross Over
Relief Valve
Direction Control Valves
7/28/2019 Industrial Hydraulic Systems
43/58
6/18/2013Welcome to the World of Fluid Power 43
Direction Control Valves
Direction Control Valves are the control elements which provide
movement to the Linear as well as Rotary actuators. In doing so theyprovide to actuators START, STOP & CHANGE of DIRECTION
functions in every Hydraulic Circuit.
Direction Control Valves can be divided into following categories
1. Spool Valves
2. Cartridge Valves
Functional Classification of DC Valves
1. Valve Body with Spool/Poppet
2. Valve Operating System
DC Valves can be Operated by the following means
7/28/2019 Industrial Hydraulic Systems
44/58
6/18/2013Welcome to the World of Fluid Power 44
p y g
1. Manual Operation
2. Mechanical Operation
3. Hydraulic Operation
4. Pneumatic Operation
5. Electrical Operation
DC Valves (Spool Valves)
7/28/2019 Industrial Hydraulic Systems
45/58
6/18/2013Welcome to the World of Fluid Power 45
DC Valves (Spool Valves)
DC Valves are further classified by their number of positions and their
center configuration
1. Two Position Valves
2. Three Position Valves
21
21 3
P T
A B
DC Valve Spool Design
7/28/2019 Industrial Hydraulic Systems
46/58
6/18/2013Welcome to the World of Fluid Power 46
DC Valve Spool Design
Spool edges play an important role in controlling the fluid and that iswhy these edges are called controlling edges.
Imagine that a spool is opening to provide flow, if this opening is sudden
then NO-flow to FULL-flow or FULL Flow to NO Flow condition will
appear quickly and this will cause a pressure shock (Pressure Surge).
Pressure Shock= 3 to 4 times of Working Pressure
Pressure shock can cause Seal failure, Pressure Gauge & Fitting Failure.
Spool Land Groove
P
7/28/2019 Industrial Hydraulic Systems
47/58
6/18/2013Welcome to the World of Fluid Power 47
t
P
Set Value
Time for which PS appeared
We can clearly observe that the pressure shock rises over and above theworking pressure, taking this into consideration we must control the
sudden rising pressure, the control is dependant on the following two
factors
1. Geometry of the Control Edge
2. Shift Speed of the Spool
Pressure Surge
How to Reduce the Magnitude of the Pressure Surge
7/28/2019 Industrial Hydraulic Systems
48/58
6/18/2013Welcome to the World of Fluid Power 48
T A P B T
ow o educe e g ude o e essu e Su ge
It is possible to reduce the effect of pressure surge by introducing the V-
Shape grooves on the periphery of the Control Edge of the Spool and by
limiting the shift speed of the spool itself.
What actually we are trying is to increase the flow rate gradually
between the two Ports by increasing the spool opening slowly thus
accelerating the load in a controlled manner.
Direction Control Valve in a Circuit
7/28/2019 Industrial Hydraulic Systems
49/58
6/18/2013Welcome to the World of Fluid Power 49
Using a 2/2 Solenoid operated DC valve
we can achieve a digital control of a
Hydraulic cylinder.
Four numbers of 2/2 solenoid operated
valves are arranged in a fashion as shown
in the figure, now switching through
electrical current is possible by a PLC to
provide a precise digital control
Arranging digital valves into a hydraulic integrated circuit allows them toaccomplish the same functions as discrete spool-type valves while
retaining the advantages of digital valves.
7/28/2019 Industrial Hydraulic Systems
50/58
6/18/2013Welcome to the World of Fluid Power 50
Direction control through a 4/3
Solenoid operated, Center Closed
DC Valve.
This particular valve is a multi-flow
path valve with two solenoids to
provide forward and reverse
movement of the cylinder, unlike
the previous example in which
digital functions are possible with
Four solenoids.
Advantage:
Single hardware element
Easy to maintain
7/28/2019 Industrial Hydraulic Systems
51/58
6/18/2013Welcome to the World of Fluid Power 51
A single DC valve with one
Sequence valve can control Two
Cylinders in a sequence.This circuit does not solve the
problem of controlling the pressure
of a branch circuit. That means if
cylinder one is to be operated athigher pressure and cylinder two is
to be operated at much lower
pressure then it would not be
possible by this circuit
Controlling Branch Pressure
7/28/2019 Industrial Hydraulic Systems
52/58
6/18/2013Welcome to the World of Fluid Power 52
Controlling Branch Pressure
By introducing a pressure
reducing valve we can easily
control the branch pressure,
because a reducing valve willclose whenever require
pressure is reached in the
branch.
Flow Control Valves
7/28/2019 Industrial Hydraulic Systems
53/58
6/18/2013Welcome to the World of Fluid Power 53
Flow Control Valves
Flow-control valves include simple orifices to sophisticated closed-
loop electrohydraulic valves that automatically adjust to variations
in pressure and temperature.
The purpose of flow control in a
hydraulic system is to regulate
speed.
All the devices discussed here
control the speed of an actuator by
regulating the flow rate.
Flow rate also determines rate ofenergy transfer at any given
pressure.
7/28/2019 Industrial Hydraulic Systems
54/58
6/18/2013Welcome to the World of Fluid Power54
The two are related in that the actuator force multiplied by the
distance through which it moves (stroke) equals the work done on
the load.
The energy transferred must also equal the work done. Actuator
speed determines the rate of energy transfer (i.e., horsepower), and
speed is thus a function of flow rate.
Directional control, on the other hand, does not deal primarily with
energy control, but rather with directing the energy transfer systemto the proper place in the system at the proper time.
Diff t T f Fl t
7/28/2019 Industrial Hydraulic Systems
55/58
6/18/2013Welcome to the World of Fluid Power55
Different Types of Flow measurement
Controlling flow of a fluid-power system does not necessarily meanregulating volume per unit of time from a valve.
Flow rate can be specified in three different ways, so it is important
to be aware of how flow is to be specified or measured:
1. Volumetric flow rate (Qv)
2. Weight flow rate(Qw)
3. Mass flow rate (Qg)
Control of Flow Rate with Valves
7/28/2019 Industrial Hydraulic Systems
56/58
6/18/2013Welcome to the World of Fluid Power56
There are eight types of flow-control valves:
Orifices - A simple orifice in the line,
Figure 1(a), is the most elementarymethod for controlling flow.
Fig. 1. Simple fixed orifice (a) and
variable orifice (b) flow controls.
Flow regulators - This device, Figure
2, which is slightly more sophisticated
than a fixed orifice, consists of an
orifice that senses flow rate as a
pressure drop across the orifice; a
compensating piston adjusts to
variations in inlet and outlet pressures.
Bypass flow regulators - In this flow
7/28/2019 Industrial Hydraulic Systems
57/58
6/18/2013Welcome to the World of Fluid Power57
yp g
regulator, flow in excess of set flow rate
returns to reservoir through a bypass port,
Figure 3. Flow rate is controlled by
throttling fluid across a variable orificeregulated by the compensator piston. The
bypass flow regulator is more efficient
than a standard flow regulator.
Demand-compensated flow controls -
Flow controls can also bypass excess
system flow to a secondary circuit, Figure
4. Fluid is routed at a controlled flow rate
to the primary circuit, and bypass fluidcan be used for work functions in
secondary circuits without affecting the
primary one.
Pressure-compensated, variable flow
7/28/2019 Industrial Hydraulic Systems
58/58
valves - This flow control is equipped with anadjustable variable orifice placed in series with
a compensator. The compensator automatically
adjusts to varying inlet and load pressures,
maintaining an essentially constant flow rate
under these operating conditions to accuracies
of 3% to 5%, Figure 5. .
Pressure- and temperature-compensated,
variable flow valves - Because the viscosity ofhydraulic oil varies with temperature (as do the
clearances between a valve's moving parts),
output of a flow-control valve may tend to drift
with temperature changes. To offset the effects
of such temperature variations, temperature
compensators adjust the control orifice openings
to correct the effects of viscosity changes
caused by temperature fluctuations of the fluid,
Figure 6.