Fluid Power Transmission

Md. Mohiuddin

Lecturer

Department of Mechanical Engineering

ME 4012

Pneumatics

Pneumatic System

• Pneumatic systems are power transmission and control systems that rely on pressurized gases.
• They utilize pressurized gases for power transmission and control.
• Pneumatic systems use air as their fluid medium.
• The preference for air is due to its safety, affordability, and widespread availability.

Pneumatic System

• It is particularly safe in environments where an electrical spark could ignite leaks from system components.
• Liquids exhibit greater inertia than gases. Therefore, in hydraulic systems the weight of oil is a potential problem when accelerating and decelerating actuators and when suddenly opening and closing valves.
• Liquids also exhibit greater viscosity than gases. This results in larger frictional pressure and power losses.
• Also, since hydraulic systems use a fluid foreign to the atmosphere, they require special reservoirs and no-leak system designs.

Choice of Working Medium

• If the system requirement is high pressure and high precision.
• When the power requirement is high like in forging presses, or sheet metal presses, it is impossible to use an air system.
• If the temperate variation range in the system is large, then the use of an air system may run into condensation problems, and oil is preferred.

• Hydraulic System

• When the system requirement is a high speed, medium pressure (usually 6 to 8 bar), and less accuracy of position
• where quick response of actuator is required
• Air is non-explosive, it is preferred where fire/electric hazards are expected
• Because air contains oxygen (about 20%) and is not sufficient alone to provide adequate lubrication of moving parts and seals, oil is usually introduced into the air stream near the actuator to provide this lubrication preventing excessive wear and oxidation.

• Pneumatic System

Comparison between Hydraulic and Pneumatic

Advantages of Pneumatic System

• Low inertia effect of pneumatic components due to low density of air.
• Pneumatic Systems are light in weight
• Operating elements are cheaper and easy to operate
• Power losses are less due to the low viscosity of air.
• High output-to-weight ratio
• Pneumatic systems offer a safe power source in an explosive environment.
• Leakage is less and does not influence the systems.
• Moreover, leakage is not harmful.
• Infinite availability of the source
• Can be stored and easily utilized

• Advantages

Disadvantages of Pneumatic System

• Suitable only for low pressure and hence low force applications.
• economical up to 50 kN only
• Generation of compressed air is expensive compared to electricity
• Exhaust air noise is unpleasant and silence has to be used
• Weight to pressure ratio is large
• Less precise. It is not possible to achieve uniform speed due to the compressibility of air.
• vulnerable to dirt and contamination
• Can easily leak

• Disadvantages

Why compressed Air

• Compressed air is a mixture of all gases contained in the atmosphere.
• Compressed air is referred to as a gas when it is used as a fluid medium.
• The unlimited supply of air and the ease of compression make compressed air the most widely used fluid for pneumatic systems.
• Although moisture and solid particles must be removed from the air, it does not require the extensive distillation or separation process required in the production of other gases.

Compressed Air

• Air is available in unlimited quantities
• easily conveyed in pipelines even over longer distances.
• Comparatively easier storage
• It can be vented to the atmosphere after it has performed work
• Compressed air is insensitive to temperature fluctuation. This ensures reliable operation even in extreme temperature conditions
• Compressed air is clean. This is especially important in the food, pharmaceutical, textile, and beverage industries
• Operating elements for compressed air operation are of simple and inexpensive construction
• Compressed air is fast. Thus, high operational speed can be attained

• Advantages

Compressed Air

• Compressed air requires good conditioning. No dirt or moisture residues may be contained in it. Dirt and dust lead to wear on tools and equipment.
• It is not possible to achieve uniform and constant piston speeds (air is compressible).
• Compressed air is economical only up to a certain force expenditure. Owing to the commonly used pressure of 7 bar the limit is about 20 to 50 kN, depending on the travel and the speed. If the force that is required exceeds this level, hydraulics is preferred.
• The exhaust is loud.
• The oil mist mixed with the air for lubricating the equipment escapes with the exhaust to the atmosphere.
• Air due to its low conductivity, cannot dissipate heat as much as hydraulic fluid.
• Air cannot seal the fine gaps between the moving parts, unlike hydraulic system.
• Air is not a good lubricating medium, unlike hydraulic fluid.

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• Disadvantages

Safety Precaution

Applications of Pneumatic System

• Manufacturing: Pneumatic systems are widely used in manufacturing processes for tasks like gripping, lifting, and positioning items on assembly lines.
• Automation: Industrial robots and automated machinery often use pneumatic components for precise control and motion.
• Packaging: Pneumatic systems help package products by sealing, labeling, and filling containers efficiently.
• Transportation: Many braking systems in vehicles, including trucks and buses, utilize pneumatic technology.
• HVAC Systems: Pneumatic actuators are used in heating, ventilation, and air conditioning systems to control dampers and valves.

Applications of Pneumatic System

• Medical Equipment: Pneumatic systems are used in medical devices such as dental tools, and patient lifts.
• Aerospace: Aircraft rely on pneumatic systems for functions like landing gear extension and retraction.
• Construction: Pneumatic tools like jackhammers, nail guns, and pneumatic drills are common in the construction industry.
• Food and Beverage: Pneumatic systems handle processes like food sorting, filling, and packaging in the food industry.

Basic Component and their Function in Pneumatic

Basic Component and their Function in Pneumatic

• An external power source, typically a motor, drives the compressor.
• Compressors are employed to pressurize ambient air drawn from the atmosphere.
• Storage reservoirs are used to store specific volumes of compressed air.
• Valves are instrumental in managing the direction, flow rate, and pressure of the compressed air.
• Piping systems facilitate the transfer of pressurized air from one location to another.
• Pneumatic actuators transform fluid power into mechanical energy for practical tasks.
• An air filter serves the purpose of eliminating contaminants such as dirt, dust, and moisture from incoming ambient air prior to its delivery to the compressor.
• Air coolers are utilized to lower the temperature of compressed air, a crucial function as air heats up significantly during the compression process.

• Functions

Stages of Air Preparation

• Stage 1: This consists of an air intake system.
• Stage 2: This stage consists of compressors, cooling, waste heat recovery, and air inlet filtration.
• Stage 3: This stage includes Conditioning equipment, consisting of air receivers (Compressed air tank), aftercoolers, separators, traps (frequently called drain traps or drains), filters, and air dryers.
• Stage 4: This stage consists of air distribution subsystems, including main trunk lines, valving, additional filters and traps(drains), air hoses, possible supplement air conditioning equipment, connectors, often pressure regulators and lubricators.

AfterCooler

• An aftercooler is a heat exchanger that has two functions.
1. it serves to cool the hot air discharged from the compressor to a desirable level before it enters the receiver.
2. it removes most of the moisture from the air discharged from the compressor by virtue of cooling the air to a lower temperature.
• an aftercooler is installed in the airline between the compressor and the air receiver.
• In this aftercooler, the moist air from the compressor flows on the outside of tubes inside of which flows cool water.
• The water flows in an opposite direction to the airflow.
• The tubes contain internal baffles to provide proper water velocity and turbulence for high heat transfer rates.
• After passing around the tubes, the cooled air enters the moisture-separating chamber, which effectively traps out condensed moisture

Air Dryer

• Aftercoolers remove only about 85% of the moisture from the air leaving the compressor. Air dryers are installed downstream of aftercoolers when it is important to remove more moisture from the air.
• There are three basic types of air dryers:
1. Chemical air dryers: In chemical air dryers, moisture is absorbed by pellets made of dryer agent materials, such as dehydrated chalk or calcium chloride. A chemical process turns the pellets into a liquid that is drained from the system. The pellets are replaced on a planned maintenance schedule.
2. Adsorption dryers remove moisture, using beds made of materials such as activated alumina or silica gel. This is a mechanical process that involves capturing moisture in the pores of the bed material. On a planned maintenance schedule, the beds are reactivated by the application of heat and a dryer gas.
3. Refrigeration dryers are refrigerators that use commercial refrigerants. In these dryers, the moist air passes through a heat exchanger where it is cooled as it flows around coils containing a liquid refrigerant.

Type of compressor

Piston Compressor

• Suction Process
• As the piston moves downward, the suction process begins. The low-pressure gas is sucked into the cylinder until the piston moves to the bottom dead center.
• Compression Process
• When the piston is in the lowest position, the cylinder is filled with low-pressure air. Driven by the crankshaft and connecting rod, the piston starts to move upward. At this time, the suction valve is closed, the working volume of the cylinder is gradually reduced, the gas in the cylinder is compressed, and the pressure is gradually increased.

• Working

Piston Compressor

• Exhaust Process
• When the exhaust valve is opened, the high-pressure air in the cylinder is discharged out of the cylinder under constant pressure until the piston reaches the top position.

• Working

Piston Compressor

• Piston-type compressors are available in a wide range of capacities and pressure.
• Very high air pressure (250 bar) and air volume flow rate are possible with multi-staging.
• Better mechanical balancing is possible by multistage compressors by proper cylinder arrangement.
• High overall efficiency compared to other compressor.

• Advantages

• Reciprocating piston compressors generate inertia forces that shake the machine. Therefore, a rigid frame, fixed to a solid foundation is often required.
• Reciprocating piston machines deliver a pulsating flow of air. Properly sized pulsation damping chambers or receiver tanks are required.
• They are suited for small volumes of air at high pressures.

• Disadvantages

Comparison among compressors

Sources of Air Contamination

• Air Quality Intake: Air compressors pull in a significant volume of air from the surrounding environment, which often contains numerous airborne contaminants.

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• Air Compressor Type and Operation: The air compressor itself can introduce contaminants, including wear particles, coolants, and lubricants.

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• Compressed Air Storage Systems and Distribution System: The air receiver and system piping are designed to store and distribute the compressed air, thereby they also may add contaminants.

Air Filter

• Air to be filtered is drawn into the filter, creating a swirling motion of air due to the presence of a deflector.
• This centrifugal action causes large contaminants and water vapor to be flung out and collected at the bottom.
• The filter cartridge provides a random zig-zag passage for the airflow, which arrests solid particles in the cartridge passage.
• A baffle plate is included to prevent turbulent air from splashing water into the filter cartridge.
• The accumulated water and other solid particles at the bottom of the filter bowl are drained off with the use of an on-off drain valve located at the bottom of the filter bowl.

Air Pressure Regulator

• The primary role of an air pressure regulator is to ensure that the working pressure in a pneumatic system remains virtually constant, despite fluctuations in the line pressure or variations in air consumption.
• If the pressure in a pneumatic system is too low, it can lead to poor system efficiency.
• When the pressure is too high, excess energy is wasted.
• Provides additional safety to the system.
• Reduces pressure in the system to the minimum required value.
• In pneumatic system, pressure fluctuations occur due to variation in supply pressure or load pressure.

Air Pressure Regulator

• Airflow enters the regulator at point A. When the adjustment knob is turned clockwise (when viewed from the knob's end), it compresses spring C. This compression action causes diaphragm D and main valve E to move, enabling airflow to pass through the valve seat area.
• Pressure in the downstream area is monitored through aspirator tube F, which is connected to area H above diaphragm D. As downstream pressure increases, it counteracts the force of the compressed spring C. Consequently, diaphragm D and valve E move to close the valve, halting airflow through the regulator. At this point, the holding pressure of the spring and the downstream pressure in area H are balanced, resulting in reduced outlet pressure.

• Working

Air Pressure Regulator

• Any downstream demand for airflow, such as opening a valve, causes downstream pressure to decrease. Spring C then pushes open valve E again, and this cycle repeats in a modulating fashion to maintain the desired downstream pressure setting.
• If downstream pressure exceeds the set pressure, diaphragm D lifts off the top of valve stem J, relieving excess pressure to the atmosphere under knob B.
• Once downstream pressure returns to the set pressure, diaphragm reseats on the valve stem, and the system returns to equilibrium.

• Working

Air Lubricators

• The operation follows a principle similar to that of a carburetor, as illustrated in the schematic diagram in the figure.
• When air enters the lubricator, its velocity increases as it passes through a venture ring. At the venture ring, the pressure is lower than atmospheric pressure, while the pressure on the oil remains atmospheric.
• This pressure difference between the upper chamber and lower chamber causes oil to be drawn up in a riser tube.
• As the oil is drawn up, it mixes with the incoming air, forming a fine mist.
• To control the rate of oil flow, a needle valve is used to adjust the pressure differential across the oil jet.
• The air-oil mixture is then forced to swirl, allowing larger oil particles to be directed back into the bowl due to centrifugal force, while only the mist continues to the outlet.

• Working

Typical Oil Used for Air Lubrication

FRL/ Service Unit

The combination of filter, regulator, and lubricator is called FRL unit or service unit. Figure (a) gives the three dimensional view of a FRL unit. Figure (b) gives a detailed symbol of the FRL unit. Figure (c) gives a simplified symbol of a FRL unit.

Pneumatic Actuators

Pneumatic Actuators

• Pneumatic actuators are devices used for converting the pressure energy of compressed air into mechanical energy to perform useful work.
• The pressurized air from the compressor is supplied to the reservoir.
• The pressurized air from the reservoir is supplied to the pneumatic actuator to do work.
• Pneumatic actuators can be used to get linear, rotary, and oscillatory motion. There are three types of pneumatic actuators:
1. Linear Actuators or Pneumatic cylinders
2. Rotary Actuators or Air motors
3. Limited angle Actuators

Classification of Pneumatic Actuators

1. Based on the application for which air cylinders are used
1. Light-duty air cylinders
2. Medium duty air cylinders
3. Heavy duty air cylinders
2. Based on the cylinder action
• Single-acting cylinder
• Double-acting cylinder
1. Single Rod Type Double Acting Cylinder
2. Double Rod Type Double Acting Cylinder
3. Based on the cylinder’s movement
• Rotating type air cylinder
• Non-rotating type air cylinder

Classification of Pneumatic Actuators

4. Based on the cylinder’s design
1. Telescopic cylinder
2. Tandem cylinder
3. Rod less cylinder
1. Cable cylinder
2. Sealing band Cylinder with slotted cylinder barrel
3. Cylinder with Magnetically Coupled Slide
4. Impact cylinder
5. Duplex cylinders
6. Cylinders with sensors

Material for Construction of Light, Medium and Heavy Duty Cylinder

Linear Actuator- Single acting cylinder

• Spring Return Piston Type

Linear Actuator- Single acting cylinder

• Gravity Return Piston Type

Linear Actuator- Single acting cylinder

• Diaphragm Type

• This represents the most basic type of single-acting cylinder.
• In a diaphragm cylinder, the traditional piston is substituted with a diaphragm made of hard rubber, plastic, or metal. This diaphragm is clamped between two halves of a metal casing, forming a wide, flat enclosure.
• Pneumatic pressure is introduced into this enclosure, exerting pressure on the diaphragm.
• As the pneumatic pressure increases and acts on the diaphragm, it applies force against a spring, resulting in the movement of the actuator stem.
• Reducing the pneumatic pressure causes the spring to retract the diaphragm.

Linear Actuator- Single acting cylinder

• Rolling Diaphragm Type

• Rolling diaphragm cylinders are similar to diaphragm cylinders.
• They consist of a diaphragm rather than a piston, and this diaphragm rolls out along the inner walls of the cylinder when air pressure is applied.
• The application of air pressure causes the diaphragm to move, which, in turn, causes the operating stem to move outward.
• Due to rolling action of the diaphragm, compared to standard diaphragm cylinders, rolling diaphragm cylinders are capable of achieving significantly longer operating strokes, typically ranging from 50 mm to 800 mm.

Linear Actuator- Double acting cylinder

Linear Actuator

• Telescopic Cylinder

• Tandem Cylinder

Linear Actuator- Rodless Cylinder

• A rodless air cylinder distinguishes itself from a standard air cylinder by not having a piston rod extend outside the cylinder body.
• Instead, it utilizes an internal piston that is connected to an external carriage through a magnetic or mechanical coupling system.
• There are three types of rodless cylinders
1. Cable Cylinder
2. Sealing band Cylinder with slotted cylinder barrel
3. Cylinder with Magnetically Coupled Slide

Linear Actuator- Rodless Cylinder

• Cable Cylinder

• This cylinder is used for long strokes, reaching up to 2000 mm.
• It consists of a nylon-jacketed cable that enters the cylinder barrel, attaches to one end of the internal cylinder, exits through a gland seal, and re-enters the other end of the internal cylinder through another gland seal.
• When compressed air is introduced into the cylinder, it pushes the piston from one end to the other.
• The cables connected to both sides of the piston, extending beyond the cylinder's ends, move in tandem.
• Cable cylinders are cost-effective and simple in design.
• However, wear and tear on the cables can lead to inaccuracies in carrier positioning and potential leakage issues.

Linear Actuator- Rodless Cylinder

• Cylinder with Magnetically Coupled Slide

• The piston has a powerful magnet that bonds the piston inside the cylinder with the carriage outside which also contains a powerful magnet.

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• Advantages are:
1. There is no leakage
2. There is no direct contact with moving elements therefore the wear is less
3. The orientation of the carriage can be changed easily

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Rotary Actuator

• Rotary actuators are used to attain angular motion.
• These devices generate high torque and offer restricted rotary motion, with common rotation options including 90 degrees, 180 degrees, and 270 degrees.
• Classification
1. Vane-type limited rotation motors
1. Single vane rotation motor
2. Double vane rotation motor
2. Rotary Actuator of Rack and Pinion Type
3. Helix spine rotary actuator
4. Axial piston air motor
5. Radial Piston air motor

Rotary Actuator- Vane type

Single Vane

Double Vane

Rotary Actuator- Rack and Pinion Type

• These actuators contain double pistons that efficiently transmit the rotary force to the output shaft.
• The piston rods have teeth and interact with the output shaft in a rack-and-pinion configuration.
• Each piston and toothed rod is constructed as a single integrated unit.
• This rack-and-pinion setup ensures a uniform distribution of torque throughout the rotational movement.
• When activated, the piston moves linearly, causing the pinion to rotate.
• The center of the pinion is connected to a shaft.

Rotary Actuator- Axial and Rotary Piston Air Motor

• The five-cylinder piston design provides even torque at all speeds due to the overlap of the five power impulses occurring during each revolution of the motor.
• At least two pistons are on the power stroke at all times.
• The smooth overlapping power flow and accurate balancing make these motors vibrationless at all speeds.
• This air motor has relatively little exhaust noise, and this can be further reduced by the use of an exhaust muffler.

• Rotary Piston

• An axial piston air motor, which can deliver up to 3 HP using 100-psi air.
• This motor also has five pistons.
• At least two pistons are on the power stroke at all times, providing even torque at all speeds.

• Air Piston

Pneumatic Valves

Valve

• Valves are devices designed to control or regulate the beginning, termination, direction, pressure, or rate of flow of a pressurized fluid. This fluid can be delivered by a compressor, vacuum pump, or stored in a vessel.
• In pneumatic system, valve perform three main functions:
1. Control the air supply to power units, such as cylinders.
2. Provide signals that govern the sequence of operations.
3. Act as interlocks and safety devices.
• Based on applications, valves in a pneumatic system can be classified as
• Direction Control Valve: Regulates the direction of fluid flow in a pneumatic system.
• Non-Return Valves: Ensure that fluid flows in one direction only, preventing backflow.
• Flow Control Valves: Manage and regulate the rate of fluid flow within the system.
• Pressure Control Valves: Control the pressure levels of the fluid in the pneumatic system.

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Directional Control Valve

• The function of directional control valve is to control the direction of flow in the pneumatic circuit.
• DCVs are used to start, stop and regulate the direction of air flow and to help in the distribution of air in the required line.
• The valves can have two or more ports and fulfill various circuit functions.
• Directional control valves can be actuated by different means, such as manual actuation or solenoid actuation.

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Types of Directional Control Valve

1. Based on Construction:
1. Poppet or Seat Valves:
• Ball Seat Valve
• Disc Seat Valve
• Diaphragm Valves
2. Sliding Spool Valves:
• Longitudinal Slide Valve
• Suspended Spool Valves
• Rotary Spool Valves
2. Based on Number of Ports:
• Two-Way Valves
• Three-Way Valves

Types of Directional Control Valve

3. Four-Way Actuation Methods Classification:
1. Mechanical
2. Electrical
3. Pneumatic
4. Size of the Port Classification:
• Port sizes designated as M5, G1/8, G1/4, etc.
• M refers to Metric thread, G refers to British Standard Pipe (BSP) thread.
5. Mounting Styles Classification:
• Sub Base
• Manifold
• In-Line
• Valve Island

Ports and position

• DCVs are described by the number of port connections or ways they control.
• For example: Two way, three – way, four way valves.

Ports and position

Poppet or Seat Valves- Ball seat valve

• Figure shows the construction of a simple 2/2 normally closed ball seat valve.
• If the push button is pressed, ball will lift off from its seat and allows the air to flow from port P to port B.
• When the push button is released, spring force and air pressure keeps the ball on it’s seat and closes air flow from port P to port B.

Poppet or Seat Valves- Disc seat valve

• Figure shows the construction of a disc type 3/2 way DCV.
• When push button is released, ports 2 and 3 are connected via hollow pushbutton stem.
• If the push button is pressed, port 3 is first blocked by the moving valve stem and then valve disc is pushed down from it’s seatn so as to open the valve thus connecting port 1 and 2.
• When the push button is released, spring and air pressure from port 1 closes the valve.

Poppet or Seat Valves- Disc seat valve

1. Response of poppet valve is very fast- short stroke to provide maximum flow opening
2. They give larger opening (larger flow) of valves for a small stroke
3. The valve seats are usually simple elastic seals so wear is minimum
4. They are insensitive to dust and dirt and they are robust, seats are self cleaning
5. Maintenance is easy and economical.
6. They are inexpensive
7. They give longer service life: short stroke and few wearing parts give minimum wear and maximum life capabilities

1. The actuating force is relatively high, as it is necessary to overcome the force of the built in reset spring and the air pressure.
2. They are noisy if flow fluctuation is large.

• Advantages

• Disadvantages

Poppet or Seat Valves- Diaphragm valve

• A diaphragm valve consists of an elastomeric diaphragm and a seat where the diaphragm rests in the closed position.
• The flexible diaphragm obstructs, controls, or isolates the flow of fluids and acts as a flow control device.
• The diaphragm element flexes either upward or downward to adjust the fluid flow rate.
• When the diaphragm is pressed against its solid seat, the valve achieves a sealed state. This sealing action prevents the flow of fluids.

Hand Operated 3/2 DCV- Spool Type

• The cross-sectional views illustrate the spool design of a 3/2 DCV (normally closed).
• In the unactuated state, ports 2 and 3 are interconnected while port 1 is blocked.
• Upon activation/actuation, ports 2 and 1 establish a connection, while port 3 becomes blocked.
• Here,
• Port 2: Common port
• Port 3: Normally open port
• Port 1: Normally closed port

Pneumatically Actuated 3/2 DCV- Spool Type

• The principle is similar to the previous one.
• The only difference is that instead of hand operation, the valve is actuated by sending pressurized air through the pilot port.
• Pressurized air acting on the piston through the pilot tube causes the piston to move, therefore, connect ports 1 and 2, while blocking port 3.
• Upon the release of pressure, the spring forces the spool to move back to its normal position therefore reconnecting ports 1 and 2.

Pneumatically Actuated 4/2 DCV- Spool Type

• The valve in the Figure is a pneumatically operated 4/2 way directional control valve (DCV).
• The transition between operational states occurs through the application of pilot pressure.
• When compressed air is introduced to the pilot spool via the control port 12, it establishes a connection between ports 1 and 2, while port 4 exhausts through port 3.
• Alternatively, applying pilot pressure to port 14 results in the connection between ports 1 and 4, with port 2 exhausting through port 3.
• Disconnection of compressed air from the control line causes the pilot spool to maintain its current position until a signal from the other control side is received.

5/2 DCV- Spool Type

Pneumatically Actuated 4/2 DCV- Suspended Disc

• In this configuration, a disc is used instead of a spool.
• In a spool type valve, the spool controls the opening and closing of ports. In this type, the suspended disc controls the opening and closing of ports.
• This suspended disc is capable of being moved through the application of pilot pressure, or a solenoid, or mechanical mechanisms.
• In this particular design, the primary disc (middle) establishes a connection between port 1 and either port 4 or port 2.
• When port 1 is in connection with port 2, port 4 exhausts through port 3.
• Moving the disc in the other direction connects ports 1 and 4, with port 4 exhausting through port 3.

Pneumatically Actuated 5/2 DCV- Suspended Disc

• This suspended disc can be moved by pilot pressure at port 14 or port 12.
• When the pilot pressure acts through port 14, ports 1 - 4 and 2 - 3 are connected and 5 is blocked.
• When the air is given to pilot line 12, then 4 - 5 and 1 -2 are connected and 3 is blocked

4/3 DCV- Rotary Valves

• The rotary spool directional control valve, shown in the Figure, consisting of a circular core featuring one or more passages.
• This core is positioned within a stationary sleeve. As the core undergoes rotation within the stationary sleeve, its passages either establish or obstruct connections with the ports in the sleeve.
• The construction of a rotary spool directional control valve is illustrated in the figure.
• By rotating the handle, core gets connected to different holes to give the required configuration of the valve.
• Three distinct positions of the core are showed corresponding to handle rotation.
• The leftmost configuration of the directional control valve connects port P to B and port A to T.
• The middle configuration blocks all ports
• The rightmost setup links port P to A and port T to B.

Non Return Valves

• Non return valves permit flow of air in one direction only, the other direction through the valve being at all times blocked to the air flow.
• Among the various types of non-return valves available, those preferentially employed in pneumatic controls are as follows:
1. Check valve
2. Restrictor check valve
3. Shuttle valve
4. Quick exhaust valve
5. Two pressure valve

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Check Valve

• The check valve is a basic type of non-return valve.
• As Illustrated in the Figure, it serves the purpose of blocking airflow in one direction while It allows flow in the opposite direction with minimum pressure loss across the valve.
• The check valve becomes operational when the inlet pressure in the direction of free flow exceeds the force of the internal spring.
• This pressure difference causes the check valve to lift clear of the valve seat and allowing air to flow through the valve.
• Check valves come with various types of checks, including plug, ball, plate, or diaphragm.

Shuttle Valve

• Also referred to as a double control valve or double check valve.
• The shuttle valve is equipped with two inlets and one outlet.
• It operates by shutting off flow in the direction of the unloaded inlet.
• Simultaneously, it allows an open path from the loaded inlet to the outlet.
• The ball operates to block the airflow from the unloaded inlet by securing it against the seat on the unloaded side.
• This action is facilitated by the pressure difference between the unloaded and loaded sides, where the pressure at the loaded inlet is higher than that of the unloaded inlet.
• Commonly installed in scenarios where a power unit (such as a cylinder) or a control unit (like a valve) needs to be actuated from two separate points.

Restrictor Check Valve

• Due to their throttling function, these valves serve as flow control valves.
• Their incorporation of a check function adds a non-return valve aspect.
• The throttle of a restrictor check valve is typically adjustable, allowing for the regulation of air flow through the valve.
• The valve regulates air flow only in the direction from A to B.
• However, the inclusion of a check valve enables unrestricted airflow when the direction of the air is reversed.

Quick Exhaust Valve

• During the extension or retraction of the cylinder, compressed air is supplied to one end, while the air on the opposite side of the piston is released to the atmosphere. Usually, this involves a lengthy path through pipes and tubes to reach the exhaust port of the directional control valve.
• To overcome this, quick exhaust valves are installed at the cylinder ports. These valves allow the direct release of air to the atmosphere at the cylinder outlet port, eliminating the need for air to travel a long distance.
• A quick exhaust valve comprises a rubber seal within its body, featuring an inlet port (1), cylinder port (2), and exhaust port (3).
• When air exits the cylinder port (1), the rubber seal closes the inlet port (1) and opens the exhaust port (3), facilitating the quick release of air from inside the cylinder.

Quick Exhaust Valve (Cont’d)

• Conversely, when compressed air is introduced through the inlet port (1), the rubber seal closes the exhaust port (3) and allows air to flow to the cylinder at a standard rate through the cylinder port (2).
• In some applications, particularly those involving single-acting cylinders, a common approach is to enhance the piston speed during the retraction phase to reduce cycle time.
• This increased piston speed is achievable by minimizing the resistance to the flow of exhaust air during cylinder motion.
• The reduction in resistance is accomplished by quick releasing the exhausting air to the atmosphere, a process facilitated by the use of a Quick Exhaust Valve.

Flow Control Valve

• A flow control valve regulates the rate of airflow.
• In a flow control valve, the adjustment of airflow is achieved by modifying the valve opening through the rotation of a knob or another mechanism.
• To ensure a steady flow of air through the valve, certain flow control valves incorporate a mechanism that automatically adjusts the valve opening in response to the pressure difference between the inlet and outlet ports.

Manifold

In-line

Pressure Control Valve

• Pressure control valves control the pressure of the air flowing through the valve or confined in the system controlled by the valve.
• There are three types of pressure control valves
1. Pressure limiting valve
2. Pressure sequence valve
3. Pressure regulator or pressure-reducing valve

Pressure Limiting Valve

• A pressure limiting valve is used to prevent the pressure in a system from exceeding a permissible maximum.
• The figure shows the construction of a pressure-limiting valve.
• These valves function as safety relief devices by opening to the atmosphere when the system surpasses a predetermined pressure.
• This action releases excess pressure and ensures the safety of the system.
• Once the pressure is reduced to a safe level, the valve automatically closes again by the spring force.

Pressure Sequence Valve

• A sequence valve is employed to carry out two operations sequentially, one after the other. For instance, the first cylinder extends first, followed by the extension of the second cylinder.
• The valve contains one inlet and two outlet ports, namely outlet port 1 and outlet port 2.
• When the working fluid is introduced to the inlet port of the sequence valve, it initially flows directly to outlet port 1.
• However, the poppet of the sequence valve only lifts off from its seat and permits airflow through port 2 when the pressure exceeds a predetermined value.

Pressure Sequence Valve (Cont’d)

• When the valve is employed to extend two cylinders sequentially, it permits the flow of working fluid in the reverse direction from port 1 but prevents reverse flow through port 2. In such cases, for the retraction of the cylinder connected to port 2, an additional check valve is incorporated (In the figure the check valve is provided at the drain line)
• Sequence valve must be incorporated into a pneumatic control where a certain minimum pressure must be available for a given function and operation is not be initiated at any pressure lower than that.
• They are also used in systems containing priority air consumers when other consumers are not to be supplied with air until ample pressure is assured.

Pressure Reducing Valve

• Pressure regulators, commonly called pressure-reducing valves, maintain constant output pressure in compressed-air systems regardless of variations in input pressure or output flow.
• Regulators are a special class of valves containing integral loading, sensing, actuating, and control components.
• Available in many configurations, they can be broadly classified as general purpose, special purpose, or precision.

Electro-Pneumatic Control

• Electro-pneumatics has become a common choice for cost-effective industrial automation, finding extensive use in production, assembly, pharmaceuticals, chemicals, and packaging systems.
• In Electro-Pneumatic control, several pneumatic and electrical technologies are applied.
• Electrical signals, sourced from either AC or DC, serve as the signal medium.
• Compressed air functions as the working medium.
• Operating voltages typically range from 12V to 220V.
• Solenoid actuation activates the control valve, and the valve resetting occurs either through a spring (single solenoid) or by employing another solenoid (double solenoid valve).
• To optimize valve actuation/reset and reduce valve size and cost, pilot-assisted solenoid actuation is frequently employed.
• Control of the pneumatic system is carried out either using a combination of Relays and Contactors or with the help of Programmable Logic Controllers (PLC).

Electro-Pneumatic Control

• Relays have increasingly been replaced by programmable logic controllers to meet the growing demand for more flexible automation.
• In Electro-pneumatic controls, three important steps are involved:
1. Signal input devices: Signal generation such as switches and contactors, Various types of contact, and proximity sensors
2. Signal Processing: Use of a combination of Contactors of Relay or using Programmable Logic Controllers
3. Signal Outputs: Outputs obtained after processing are used for the activation of solenoids, indicators, or audible alarms

Electro-Pneumatic Control

• Seven basic electrical devices commonly used in the control of fluid power systems are:
1. Manually-actuated push button switches: used to close or open an electric control circuit.
2. Limit switches: Any switch that is actuated due to the position of a fluid power component (usually a piston rod or hydraulic motor shaft or the position of load is termed as a limit switch. The actuation of a limit switch provides an electrical signal that causes an appropriate system response.
3. Pressure switches: Pressure switches are used to sense a change in pressure, and open or close an electrical switch when a predetermined pressure is reached.
4. Solenoids
5. Relays: It is a simple electrical device used for signal processing.
6. Timers: Timers are required in control systems to effect time delay between work operations.
7. Temperature switches: Temperature switches automatically sense a change in temperature and open or close an electrical switch when a predetermined temperature is reached.

Electro-Pneumatic Control

• Other devices used in electro-pneumatic are
1. Proximity sensors
2. Electric counters

Seven Qualities of Air Required in Production

• Branches 1 and 2 deliver air directly from the air receiver, with standard filters and auto drains to remove condensate. Sub-branch 2 boasts higher purity due to the inclusion of a micro filter.
• Branches 3 to 6 utilize air conditioning by a refrigerated dryer. Branch 3 requires no auto drain, branch 4 needs no pre-filtering, and branch 5 achieves enhanced air purity through a micro filter and sub-micro filter, aided by the removal of moisture via a refrigerated air dryer.

Seven Qualities of Air Required in Production

• Sub-branch 6 is equipped with an odor removal filter.
• Branch 7 incorporates an additional adsorption-type dryer, ensuring the elimination of condensation risk at low temperatures.

Seven Qualities of Air Required in Production

Seven Qualities of Air Required in Production

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