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Pneumatic Valves. Lesson 4. Introduction. Compressed air and gases must be controlled to be useful. One of the advantages of pneumatic systems is the ease and precision with which the system can be controlled.
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Pneumatic Valves Lesson 4
Introduction • Compressed air and gases must be controlled to be useful. • One of the advantages of pneumatic systems is the ease and precision with which the system can be controlled. • Valves are used to control the pressure of compressed gases as well as the rate and direction of flow.
Introduction • This in turn controls the action of the device using the compressed air or gas. • Valves are used throughout industry to control compressed air and gases that industry depends on.
Pressure Control Valves • Pressure control valves are used to maintain a preset pressure in the entire air system or in just one part of the air system. • Pressure control can be achieve through 2 methods: • Pressure relief and pressure regulation. • Pressure relief valves are pressure limiting devices which keep the system pressure below a preset maximum.
Pressure Control Valves • They consist of a housing and a ball or poppet which is held in position by a spring. • This spring tension against the ball or poppet holds it against a seat and prevents air flow through the valve. • As the pressure increases, it creates a force against the ball until it overcomes the spring force and pushes the ball from its seat. • This allows the excess pressure to exhaust into the atmosphere.
Pressure Control Valves • A pressure relief valve should be designed into every compressed air system • This should be adjusted to prevent the system pressure from exceeding the pressure ratings of the components in the system. • They are usually used in combination with a pressure switch which turns the compressor on or off.
Pressure Control Valves • The pressure regulator is a valve that monitors the air pressure downstream of it and automatically opens and closes to maintain that pressure at a preselected value. • It consists of a housing, valve and valve stem, a sensing diaphram, and an adjustment spring. • The spring maintains force against the diaphram which pushes against the valve stem and holds the valve open.
Pressure Control Valves • This allows air to flow through the regulator to components located downstream. • As pressure on the downstream side of the regulator increases, it exerts force against sensing diaphram. • As the force increases it overcomes the spring force and opposes the pressure it spring exerts against the valve stem.
Pressure Control Valves • This allows the valve to close. • As downstream pressure decreases the force against the diaphram diminishes and the spring reopens the valve which allow air to flow again. • Pressure regulators should be installed at the points in the air distribution system where an air operated device is used. • This allows the air pressure to be adjusted to meet the individual requirements of each piece of equipment.
Flow Control Valves • Flow control valves are used in a pneumatic system to govern the rate at which air is allowed to flow. • They are available in 2 styles: • Needle valves and Flow controls • Needle valves control flow in both directions. • Flow controls control flow in 1 direction
Flow Control Valves • The needle valve consists of a tapered needle which can be adjusted in relation to a fixed orifice in the housing. • Moving the needle away from the orifice created less restriction and allows more flow while moving the needle closer increases the restriction and reduces the flow. • Needle valves are used where the flow needs to be controlled in both directions through the line.
Flow Control Valves • The flow control valve combines a needle valve and a check valve in one housing. • The needle valve controls the flow in one direction and the check valve allows free flow in the other direction. • The most common application for a flow control valve is to control the speeds of pneumatic cylinders and motors.
Directional Control Valves • Directional control valves are used to start, stop, and direct the flow of air in a pneumatic system. • By directing the flow of air, these valves control the action of other pneumatic devices, such as cylinders, motors, pumps, or other valves.
Directional Control Valves • Directional control valves are constructed in a variety of ways. • The main types include ball valves, poppet valves, and spool valves. • Each of these valves have specific performance characteristics that make them adaptable to particular application.
Directional Control Valves • Ball valves consist of a spherical element encased in a housing. • The element is rotated by means of a handle which extends through the housing. • As it rotates, passages machined in the ball connect and disconnect various ports in the housing to permit or interrupt air flow.
Directional Control Valves • Poppet valves are composed of moving elements called poppets, which seat against the valve housing to prevent air flow, or lift from their seat to allow flow. • They are inherently a very high flow valve with rapid response and low maintenance. • They are often used to control the air supple where high flow is required and in control circuits where rapid response time and low maintenance are of concern.
Directional Control Valves • Spool Valves are the most versatile and extensively used valve in pneumatic circuit. • They consist of a cylinder spool which slides through a cylindrical bore in a housing. • Recessed areas of the spool connect ports to provide passage through the valve while larger areas of the spool seal off other ports. • They are used to direct air flow for powering pneumatic devices.
Directional Control Valves • To control machine processes and to sense a manual or mechanical movement and initiate a signal.
Functions of Directional Control Valves • Directional control valves are classified as to the way they function? • The 3 main categories of directional control valves are 2 way, 3 way, and 4 way. • The 2 way directional control valve contains 2 working ports and 1 flow path between these ports. • The valve has 2 operating positions and is sometimes referred as a 2/2 valve.
Functions of Directional Control Valves • The 3 way directional control valve contains 3 working ports and provides 2 flow paths. • This valve also has operating positions and is sometimes referred to as a 3/2 valve. (3 way, 2 position) • 4 way directional control valves contain either 4 or 5 working ports.
Actuators & Returns • Spool valves can be actuated in a variety of ways depending upon what the function of the valve is. • Types of actuators include: • Manual, mechanical, pneumatic and electric. • Types of returns include: • Manual, Spring, pneumatic, and electric. • A manual actuator is any actuating device which is controlled directly by the operator.
Actuators & Returns • It is usually used to initiate start and stop signals to the circuit. • The common manual actuators are palm button, push button, hand lever, foot pedal, and treadle. • A mechanical actuator is any actuating device triggered by another mechanical device. • They are used to sense the location of a moving member and initiate a signal to relay this information.
Actuators & Returns • The common mechanical actuators are roller cam and cam stem. • Pneumatic Actuators receive a signal from another valve to shift the spool. • These valves are normally used as a power valve receiving their signals from smaller limit valves. • They are available in pilot and bleed
Actuators & Returns • Electric solenoid actuators all the combination of electrical circuitry with pneumatic power devices. • Electric switches send current to the solenoid to open the valve which controls the power device.
Actuators & Returns • Returns • Types of returns vary with the actuator used and the application. • The common returns include: • Manual, detent, spring, pilot, internal pilot, internal differential pilot, external differential pilot, bleed, and solenoid.
