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Chapter 2PNEUMATICS AND HYDRAULICS
1. 1 INTRODUCTION TO FLUID POWERFluid power is the technology that deals with the generation, control and transmission of power
using pressurized fluids. It can be said that fluid power is the muscle that moves the industry. This is because fluid power is used to push, pull, regulate, or drive virtually all the machines of modern industry. For example, fluid power steers and brakes automobiles, launches spacecraft, moves earth, harvests crops, mines coal, drives machine tools, controls airplanes, processes food and even drills teeth. In fact, it is almost impossible to find a manufactured product that hasn’t been “fluid-powered” in some way at some stage of its production or distribution.
Fluid power is called hydraulics when the fluid is a liquid and is called pneumatics when the fluid is a gas. Hydraulic systems use liquids such as petroleum oils, synthetic oils and water. Pneumatic systems use air as the gas medium because air is very abundant and can be readily exhausted in the atmosphere after completing its assigned task.
2.2 ADVANTAGES OF FLUID POWER
There are three basic methods of transmitting power: electrical, mechanical, and fluid power. Most applications actually use a combination of the three methods to obtain the most efficient overall system. To properly determine which method to use, it is important to know the salient features of each type. For example, fluid systems can transmit power more economically over greater distance than can mechanical types. However, fluid systems are restricted to shorter distances than are electrical systems.
The secret of fluid power’s success and widespread use is its versatility and manageability. Fluid power is not hindered by the geometry of the machine, as is the case in mechanical systems. Also, power can be transmitted in almost limitless quantities because fluid systems are not so limited by the physical limitations of materials as are electrical systems. For example, the performance of an electromagnet is limited by the saturation limit of steel. On the other hand, the power capacity of fluid systems is limited only by the physical strength of the material (such as steel) used for each component.
a. Ease and accurate control: By the use of simple levers and push buttons, the operator of a fluid power system can readily start, stop, accelerate, decelerate, reverse or position large forces with great accuracy. Instantly reversible motion with in less than half a revolution can be achieved.
b. Multiplication and variation of force: Linear or rotary force can be multiplied from a fraction of an ounce to several hundred tons of output.
c. Multifunction control: A single hydraulic pump or air compressor can provide power and control for numerous machines or machine functions when combined with fluid manifolds and valves.
d. High horse power, low weight ratio: Pneumatic components are compact and light weight. You can hold a five horse power hydraulic motor in the palm of your hand.
e. Low speed torque: Unlike electric motors, air or hydraulic motors can produce large amounts of torque (twisting force) while operating at low speeds. Some hydraulic and air motors can even maintain torque at zero speed without overheating.
f. Constant force or torque: Only fluid power systems are capable of providing constant force or torque regardless of speed changes.
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g. Safety in hazardous environment: Fluid power can be used in mines, chemical plants, near explosive and in paint applications because it is inherently spark free and can tolerate high temperatures.
2.3 DRAWBACKS OF FLUID POWERIn spite of all the previously mentioned advantages of fluid power, it is nit a panacea for all power
transmission applications. Fluid power systems also have some drawbacks. For example, hydraulic oils are missy, and leakage is very difficult to eliminate completely. Hydraulic lines can burst, possibly resulting in injuries to people due to high-speed oil jets and flying pieces of metal if proper design is not implemented. Prolonged exposure to loud noise, such as that emanating from pumps, can result loss of hearing. Also, most hydraulic oils can cause fires if an oil leak occurs in an area of hot equipment. In pneumatic systems, components such as compressed air tanks and accumulators are potentially explosive if the pressure is allowed to increase beyond safe design limits.
2.4 FLUID POWER APPLICATIONS
a. Mobile: Here fluid power is used to transport, excavate and lift materials as well as control or power the mobile equipments. End use industries include construction, agriculture, marine and the military. Applications include backhoes, graders, tractors, truck brakes and suspensions, spreaders and highway maintenance vehicles.
b. Industry: Here fluid power is used to provide transmission and motion control for the machines of industry. End use in industries ranges from plastic working to paper production.
c. Applications include metal working equipment; controllers automated manipulators, material handling and assembly equipment.
d. Aerospace: Fluid power is used for both commercial and military aircrafts, spacecraft and related support equipment. Applications include landing gear, brakes, flight controls, motor control and cargo landing equipment.
2.5 COMPONENTS OF A PNEUMATIC SYSTEMPneumatic systems have components that are similar to those used in hydraulic systems. Essentially
the following six basic components are required for pneumatic systems.
1. A compressor to compress the air that comes directly from the atmosphere.2. An air tank to store a given volume of compressed air.3. An electric motor or other prime mover to drive the compressor.4. Valves to control air direction, pressure, and flow rate.5. An actuator to converts the air pressure into mechanical force or torque to do useful work.6. Piping to carry the pressurized air from one location to another.
2.5.1 Supply & service equipment
The compressed air supply for a pneumatic system should be adequately calculated and made available in the appropriate quality.
Air is compressed by the air compressor and delivered to an air distribution system in the factory. To ensure the quality of the air is acceptable, air service equipment is utilized to prepare the air before being applied to the control system.
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Figure 2.1: Compressor setup
As a rule pneumatic component are designed for a maximum operating pressure of 8-10 bar but in practice it is recommended to operate at between 5 and 6 bars for economic use.
A reservoir should be fitted to reduce pressure fluctuations. In some cases, the term receiver is also used to describe a reservoir.Shut-off valves can be used to block sections of compressed air lines if these are not required or need to be closed down for repair or maintenance purposes.
The air service unit is a combination of the following
1. Compressed air filter (with water separator)2. Compressed air regulator3. Compressed air lubricator
An air service unit is fitted at each control system in the network to ensure the quality of air for each individual task.
Figure 2.2: Service unit
The compressed air filter has the job of removing all contaminants from the compressed air flowing through it as well as water which has already condensed. The compressed air enters the filter bowl through guide slots.
Liquid particles and larger particles of dirt are separated centrifugally collecting in the lower part of the filter bowl. The collected condensate must be drained before the level exceeds the maximum condensate mark, as it will otherwise be re-entrained in the air stream.
The purpose of the regulator is to keep the operating pressure of the system (secondary pressure) virtually constant regardless of fluctuations in the line pressure (primary pressure) and the air consumption.
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The purpose of the lubricator is to deliver a metered quantity of oil mist into a leg of the air distribution system when necessary for the operation of the pneumatic system.
2.5.2 VALVESThe function of valves is to control the pressure or flow rate of pressure media. Depending on
design, these can be divided in to the following categories:a. Direction control valves
1. Input/signaling elements 2. Processing elements 3. Control elements
b. Flow control valvec. Non-return valved. Pressure control valvee. Shut-off valves
2.5.2.1 Direction control valves
The direction control valve controls the passage of air signals by generating, cancelling or redirecting signals.
The valve described by
1. Number of ports or openings (ways) : 2-way, 3-way, 4way, etc.
2. Number of positions : 2 positions, 3 positions, etc.
3. Methods of actuation of the valve : Manually actuated, mechanically actuated, pneumatically actuated, electrically actuated.
4. Methods of return actuation : Spring return, air return, etc.
As a signaling element the directional control valve is operated for example, by a roller lever to detect the rod position of a cylinder.
Figure 2.3: Input signaling Elements(3/2 way roller lever valve, without and with idle return)
As a processing element the directional control valve redirects or cancels signals depending on the signal inputs received.
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Figure 2.4: Processing Element (3/2 way air actuated valve, single pilot valve with spring return)
As a control element the direction control valve must deliver the required quality of air to match the power component requirements.
Figure 2.5: Control Element (5/2 way double pilot valve)
2.5.2.2 Flow control valves
The flow control valve restricts or throttles the air in a particular direction to reduce the flow rate of the air and hence control the signal flow. Ideally it should be possible to infinitely vary the restrictor from fully open to completely close.
The flow control valve should be fitted as close to the working element as is possible and must be adjusted to match the requirements of the application. If the flow control valve is fitted with a check valve then the function of flow-control is unidirectional with full free flow in one direction.
Flow control valve, adjustable
One-way flow control valve
Figure 2.6: Flow control valve
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2.5.2.3 Non-return valve
The non-return valve allows a signal to flow through the device in one direction and in the other direction blocks the flow. Amongst others, this principle is applied in shuttle valves or quick exhaust valves. The non-return valve in the form of a basic element of other valve types is shown in a broken outline in the illustration below.
Non-return valve and its derivatives
Check valve
Check valve with spring return
Shuttle valve
Dual pressure valve
Quick exhaust valve
Figure 2.7: Non-return valve and its derivatives
2.5.2.4 Pressure control valves
Pressure control valves are three main groups a. Pressure limiting valves b. Pressure regulating valves c. Pressure sequence valves
The pressure limiting valves are utilized on the up-stream side of the compressor to ensure the receiver pressure is limited, for safety, and that the supply pressure to the system is set to the correct pressure.
The pressure regulating valve keeps the pressure constant irrespective of any pressure fluctuations in the system. The valve regulates the pressure via a built-in diaphragm.
The pressure sequence valve is used if a pressure-dependent signal is required for the advancing of a control system.
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Figure2.8: Pressure sequence valve
When the applied control signal reaches the set pressure, the 3/2-way valve incorporated at this point is actuated. Conversely, the valve reverses, if the control signal falls below the set pressure.
2.5.2.5 Combination valvesThe combined functions of various elements can produce a new function. An example is the time
delay valve which is the combination of a one-way flow control valve, a reservoir and a 3/2-way directional control valve.
Figure 2.9: Time delay valve
Depending on the setting of the throttling screw, a greater or lesser amount of air flows per unit of time into the air reservoir.
When the necessary control pressure has built up, the valve switches to through flow. This switching position is maintained for as long as the control signal is applied.
2.5.3 Processing ElementsTo support the directional control valves at the processing level, there are various elements which
condition the control signals for a task. The elements are
a. Dual pressure valve (AND function)b. Shuttle valve (OR function)
A shuttle valve permits the combination of two input signals into an OR function. The OR gate has two inputs and one output. An output signal is generated, if pressure is applied at one of the two inputs.
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Shuttle valve
Dual pressure valve
Figure 2.10: Processing elements
2.5.4 Power componentsThe power section consists of control elements and power components or actuators. The actuator
group includes various types of linear and rotary actuators of varying size and construction. The actuators are complemented by the control elements, which transfer the required quantity of air to drive the actuator. Normally this valve will be directly connected to the main air supply and fitted close to the actuator to minimize losses due to resistance.
Actuators can be further broken down into groups
a. Linear actuators - Single-acting cylinder
- Double-acting cylinder
b. Rotary actuators
- Air motors - Rotary actuators
Figure 2.11: Actuators (Linear and rotary)
2.6 Hydraulics and Hydraulic componentsHydraulics is the application of liquids to effect mechanical motion or work. In hydraulics water or
oil are used as working medium. Hydraulic fluid characteristics have a crucial effect on equipment performance and life. It is
important to use a clean, high-quality fluid in order to achieve efficient hydraulic system operation.
It is usually petroleum oil with various additives. Some hydraulic machines require fire resistant fluids, depending on their applications.
In addition to transferring energy, hydraulic fluid needs to lubricate components, dissipate heat, and suspend contaminants and metal filings for transport to the filter.
2.6.1 Components of a Hydraulic system Essentially the following six basic components are required for hydraulic systems:
1. A tank (reservoir) to hold the hydraulic oil2. A pump to force the oil through the system3. An electric motor or other power source to drive the pump4. Valves to control oil direction, pressure, and flow rate
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5. An actuator to converts the pressure of the oil into mechanical force or torque to do useful work. Actuators can either be cylinders to provide linear motion or motors(hydraulic) to provide rotary motion
6. Piping, which carries the oil from one location to another
2.6.1.1 Hydraulic pumps Hydraulic pumps supply fluid to the components in the system. Pressure in the system develops in
reaction to the load. Hence, a pump rated for 5,000 psi is capable of maintaining flow against a load of 5,000 psi.
Pumps have a power density about ten times greater than an electric motor (by volume). They are powered by an electric motor or an engine, connected through gears, belts. Common types of hydraulic pumps to hydraulic machinery applications are;
a. Gear pump: cheap, durable, simple. Less efficient, because they are constant displacement, and mainly suitable for pressures below 20 Mpa (3000 psi).
b. Vane pump: cheap and simple, reliable (especially in g-rotor form). Good for higher-flow low-pressure output.
c. Axial piston pump: many designed with a variable displacement mechanism, to vary output flow for automatic control of pressure. There are various axial piston pump designs, including swash plate (sometimes referred to as a valve plate pump) and check ball (sometimes referred to as a wobble plate pump). The most common is the swash plate pump. A variable-angle swash plate causes the pistons to reciprocate.
d. Radial piston pump: A pump that is normally used for very high pressure at small flows.
Piston pumps are more expensive than gear or vane pumps, but provide longer life operating at higher pressure, with difficult fluids and longer continuous duty cycles.
Fig 2.12 Gear pump
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2.6.1.2 Valves and other components
The function of valves is to control the pressure or flow rate of pressure media. The valves and other components are similar to pneumatic systems which are already explained.
2.7 Comparison of pneumatic and hydraulic system
The basic differences between hydraulic and pneumatic systems are shown in table 2A.
S.No. HydraulicsPneumatics
1 Resistant to fluctuating load Non-resistant to fluctuating load
2 Speed is limited Very high speed is possible
3Suitable for feed movement in machine tools (shaping, grinding, etc.,)
Unsuitable for feed movement
4 Pump is necessary Air compressor is necessary
5 Very precise stroke control attainable Precise stroke control is difficult
6Operating pressure may be from low to very high(up to 1000 bar)
Operating pressure is generally 6 bar
7 Weight to pressure ratio is very small Weight to pressure ratio is large
8Cavitation is a big problem to be tackled appropriately
No such problem
9 System rigidity is good System rigidity is poor
10 Overall cost is moderate to high Overall cost is low
11 Moderate operating cost Very low operating cost
2.8 Symbols and Standards in Pneumatics & Hydraulics
The development of pneumatic systems is assisted by a uniform approach to the representation of the elements and the circuits. The symbols used for the individual elements must display the following characteristics:
a. Actuation and return actuation methodsb. Number of connections (all labeled for identification)c. Number of switching positiond. General operating principlee. Simplified representation of the flow path
The technical construction of the component is not taken into account in the abstract symbol form. The symbols used in pneumatics and hydraulics are detailed in the standard DIN ISO 1219, “Circuit symbols for fluidic equipment and systems”. The symbols for the energy supply system can be represented as
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individual elements or as combined elements. If a standard and common air supply is used for all components, then the simplified symbols can be used.
2.8.1 Directional control valve Symbol development
The representation symbols of direction control valves are listed in table 2B.
Description Symbol
Valve switching positions are represented as squares
The number of squares shows how many switching positions the valve has
Lines indicate flow paths, arrows shows the direction of flow
Shut off positions are identified in the boxes by lines drawn at right angles
The connections (inlet and outlet ports) are shown by lines on the outside of the box
Table 2B
2.8.2 Representation of directional control valves
The directional control valve is represented by the number of controlled connections, the number of positions and the flow path. In order to avoid faulty connections, all the inputs and outputs of a valve are identified.
2/2 (No. of ports/No. Of positions) - way directional Control valve, normally closed
3/2-way directional control valve, normally closed
3/2-way direction control valve, normally open
4/2-way direction control valve From 1 2 and from 4 3
5/2-way directional control valve From 1 2 and from 4 3
5/3-way directional control valve Mid position closed
Fig 2.13 Valves and their representation
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2.8.3 Designation of direction control valves
A numbering system is used to designate directional control valves and is in accordance with DIN ISO 5599-3. Prior to this a lettering system was utilized and both systems of designation are presented in table 2C.
Pneumatic lines
ISO 5599-3 Lettering system
Port or connection
Working lines
1 P Pressure port
2,4 A,B Working lines
3,5 R,S Exhaust ports
Pilot lines
10 Z Applied signal inhibits flow from port 1 to port 2
12 Y,Z Applied signal connects port 1 to port 2
14 Z Applied signal connects port 1 to port 4
81,91 Pz Auxiliary pilot air
Table 2C: Illustrates the numbering and lettering system of ports
2.8.4 Methods of actuation
The methods of actuation of pneumatic directional control valves are dependent upon the requirements of the task. The types of actuations are
a. Manually actuatedb. Mechanically actuatedc. Pneumatically actuatedd. Electrically actuated ande. Combined actuation
The symbols for the methods of actuation are detailed in DIN ISO 1219.
When applied to a directional control valve, consideration must be given to the method of initial actuation of the valve and also the method of return actuation. Normally these are two separate methods. They are both shown on the symbol either side of the position boxes.
There may also be additional methods of actuation such as manual overrides, which are separately indicated in Fig 2.14.
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Manual Actuation
General
Push button
Lever Operated
Detent lever operated
Foot pedal
Electrical actuation
Single solenoid operation
Double solenoid operation
Mechanical Actuation
Plunger
Roller operated
Idle return, roller
Spring return
Spring centered
Pneumatic actuation
Direct pneumatic actuation
Indirect pneumatic actuation (piloted)
Combined actuation
Double solenoid and pilot operation with manual override
Fig 2.14 Methods of actuation13
2.8.5 Design of the circuit diagram
The structure of the circuit diagram should correspond to the control chain. Whereby the signal flow is represented from the bottom to the top. Simplified or detailed symbols may be used for the representation of the circuit diagram in Fig 2.15.
2.8.6 Circuit layoutThe layout of pneumatic circuit diagram is explained for atypical problem.
Typical problem
The piston rod of a double-acting pneumatic cylinder advances if either a manual push button or a foot pedal is operated.
The cylinder returns to its starting position slowed down after fully extending. The piston rod will return provided the manual actuators have been released.
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Solution
Fig 2.16 A model circuit diagram
The roller lever valve 1S3 is positioned as a limit switch in the forward end position of the cylinder. The circuit diagram shows this element situated at the signal input level and does not directly reflect the orientation of the valve. The mark on the circuit at the extended cylinder position indicates the physical position of the limit switch 1S3 for circuit operation.
If the control is complex and contains several working elements, the control should be broken down into separate control chains, whereby a chain is formed for each cylinder.
Wherever possible, these chains should be drawn next to each other in the same order as the operating sequence.
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2.8.7 Symbols and their description The symbols which are used in pneumatics and hydraulic circuits are described below
Description Symbol
Compressor with fixed capacity
Air reservoir with T junction
Pressure source (Pneumatic)
Filter (separation and filtration of particles)
Water separator (manually operated)
Lubricator (metered quantities of oil passed to the air stream)
Pressure regulator (Relieving type- vent hole for excess upstream pressure- adjustable)
a. Air service unit –(Filter, Regulator, Pressure gauge and shut-off valve)
b. Simplified air service unit
a. b.
Manifold
Throttle valve
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Flow control valve(restricts or throttles the flow, the arrow P to A represents pressure balance)
Spring loaded Check valve/non-return valve (it allows flow in one direction and blocks the flow in other direction)
One-way flow control valve (flow control valve is fitted with check valve, then the function of flow control is unidirectional with full free flow in one direction)
Shuttle valve/ OR gate
Quick exhaust valve
Dual pressure valve/AND gate
Shut-off valve
Pressure gauge
Single acting cylinder
Double acting cylinder
Piloted non-return valve
Branch T
3/2-way valve with push button, normally closed
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3/2-way valve with push button, normally open
3/2-way roller lever valve, normally closed
3/2-way roller lever valve with idle return, normally closed
5/2-way valve with selector switch
5/2-way single pilot valve
5/2-way double pilot valve
Pressure sequence valve
Time delay valve normally closed
Pressure sensor
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Flow rate sensor
Pressure relief valve
Pilot-operated pressure relief valve
Pressure regulator
4/2-way hand lever valve
4/3-way hand lever valve, re circulating mid-position
4/3-way hand lever valve, closed in mid position
4/3-way hand lever valve, relieving mid position
weight
Hydraulic motor
Hydraulic motor with Tacho generator
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Pressure regulator with pressure gauge
Hydraulic power pack, detailed
Hydraulic-power pack , simplified
Diaphragm accumulator, detailed
Diaphragm accumulator
Hose line
Limit switch, electrical, actuated
from the right or the left
Signal input plate, electrical
Relay,3-off
3/2-way single solenoid valve, normally closed
5/2-way double solenoid valve
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5/2-way single solenoid valve
4/2-way solenoid valve
4/3-way solenoid valve, closed in mid-position
4/3-way solenoid valve, recirculating mid-position
Indicator and distributor plate, electrical
Proximity switch with cylinder mounting
Pneumatic- electrical converter
ME102 Workshop Practice I Pneumatics
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Exercise 1. Edge Folding device
Description of the machine:
Operation of two identical valves by push button causes the forming tool of an edge folding device to thrust downwards and fold over the edge of a flat sheet of cross sectional area 40 x 5 mm.
If both - or even just one - push button is released, double-acting cylinder (1A) slowly returns to the initial position. The cylinder pressures are indicated.
The students are required to prepare the following
a. Components list
b. Circuit diagram
c. Procedure
d. Precautions if any
e. Result
ME102 Workshop Practice I Pneumatics
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Exercise 2. Marking Machine
Description of machine
Surveyor's measuring rods in 3 or 5 m length are marked in red with 200 mm graduations. There is a choice of two push buttons to start the forward movement of the measuring rods via cylinder (1 A), which has the exhaust air throttled. The idle stroke, also started by a push button, can only take place when the double-acting cylinder (1 A) has reached its forward end position.
The students are required to prepare the following
a. Components list
b. Circuit diagram
c. Procedure
d. Precautions if any
e. Result
ME 102 Workshop Practice I Pneumatics
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Exercise 3. Allocating Device
Description of machine
A double acting cylinder is to be used to transfer parts from a magazine. The cylinder moves forward and backward continuosly through a push button.The forward and backward motions of the cylinder only takes place when it reaches the forward end and retracted end positions.
The students are required to prepare the following
a. Components list
b. Circuit diagram
c. Procedure
d. Precautions if any
e. Result
ME 102 Workshop Practice I Pneumatics
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Exercise 4. Pressing Machine
Description of machine
A double-acting cylinder is used to press together glued components. Upon operation of a push button, the clamping cylinder extends.
Once the fully advanced position is reached, the cylinder is to remain for a time of T= 6 seconds and then immediately retract to the initial position. The cylinder retraction is to be adjustable. A new start cycle is only possible after the cylinder has fully retracted.
The students are required to prepare the following
a. Components list
b. Circuit diagram
c. Procedure
d. Precautions if any
e. Result
ME 102 Workshop Practice I Electro Pneumatics
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Exercise 5. Parcel Separating Device
Description of machine
The parcel separating device feeds parcel post from a sloping conveyor slide to an X-ray appliance. The double acting cylinder retracts rapidly upon actuation of a push button, and it advances slowly when the push button is released.
The students are required to prepare the following
a. Components list
b. Circuit diagram
c. Procedure
d. Precautions if any
e. Result
ME 102 Workshop Practice I Electro Pneumatics
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Exercise 6. Rotary indexing table
Description of machine
Using rotary indexing table plastic containers are to be separated in linear sequence.
By pressing a pushbutton switch the oscillating piston rod of a cylinder drives the rotary table in sequence via a pawl. When the pushbutton is pressed again, this drive is switched off.
The students are required to prepare the following
a. Components list
b. Circuit diagram (Pneumatic and electrical)
c. Procedure
d. Precautions if any
e. Result
ME 102 Workshop Practice I Hydraulics
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Exercise 7. Furnace door operating
Problem description
A furnace door is opened and closed by a double-acting cylinder. The cylinder is activated by a 4/2-way valve with spring return. This ensures that the door opens only as long as the valve is actuated. When the valve actuating lever is released, the door closes again.
The students are required to prepare the following
a. Components list
b. Circuit diagram (Hydraulic)
c. Procedure
d. Precautions if any
e. Result
ME 102 Workshop Practice I Hydraulics
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Exercise 8. Rotary Machining Station
Problem description
The load must be capable of being set to different heights. The load is raised and lowered by a hydraulic cylinder. The downward motion must be carried out smoothly and at a constant speed. The speed can be varied.
The students are required to prepare the following
a. Components list
b. Circuit diagram (Hydraulic)
c. Procedure
d. Precautions if any
e. Result
APPENDIX
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1. Control the speed of a single acting cylinder in both the forward and backward movements.
2. Direct control of a double acting cylinder by using a 5/2 lever operated direction control valve.
3. Connect the pneumatic circuits to operate the following machines:
a. The parcel separating device feeds parcel post from a sloping conveyor slid to an X-ray appliance. Operating a push button causes very rapid retraction of the single acting cylinder with the attached parcel tray. After releasing the valve actuator, the piston rod advances.
b. Two cylinders are used to transfer parts from a magazine. When a push button is pressed, the first cylinder extends and the second cylinder, and the first cylinder retracts, followed by the second cylinder.
c. Upon operation of a push button, the double acting cylinder extends. Once the fully advanced position is reached, the cylinder is to remain for a time of T=10 seconds and then immediately retract to the initial position. The cylinder retraction is to be adjustable. A new start cycle is only possible after the cylinder has fully retracted.
4. Construct electro pneumatic circuits for the following problems:
a. When two push buttons are pressed the single acting cylinder advances, if one push button is released the cylinder retracts.
b. If once a push button is pressed the double acting cylinder advances and returns automatically when it is reached forward end position.
5. Several stations on a rotary machining station are driven by a hydraulic power pack.
As individual stations are switched on and off, they produce pressure fluctuations throughout the hydraulic circuit. This effect will be studied on a drilling station. The fluctuations in pressure and the tractive forces created during drilling must not affect the feed of the drilling station. A flow control valve is to be used to ensure a smooth adjustable feed rate, while a pressure relief valve is to be used as a counter-holding valve to compensate for the tractive forces.
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