Pneumatic Control Valves 351

2/2 valve

A type of two-way directional control valve with two ways and two positions. 2/2 valves most frequently are used to only block or allow fluid flow.

3/2 valve

A directional control valve with three ways and two positions. A 3/2 valve can be either a mixing valve or a diverting valve.

4/2 valve

A directional control valve with four ways and two positions. In a 4/2 valve, one port is usually open to flow from the pump.

4/3 valve

A directional control valve with four ways and three positions. In a 4/3 valve, the three positions are normal, straight, and cross way.

actuation

The act of performing a valve function. Actuation is the point at which a valve is triggered.

actuator

A component that directly helps convert fluid energy into mechanical energy. Actuators can be such components as cylinders, motors, or rotary devices.

adjustable cap

A relief valve component that controls the resistance on the pressure spring. Adjustable caps are tightened or loosened to adjust the amount of resistance against the spring.

adjusting screw

A valve component that opens and closes to provide control capability to a valve. When the adjusting screw is unscrewed the valve is open, and when it's fully tightened the valve is closed.

air receiver

An air storage tank used with pneumatic systems. An air receiver balances air compressor capacity and airflow demand.

air-piloted directional control valve

A type of directional control valve that actuates using compressed air coming from the pilot port. Air-piloted directional control valves are sometimes used in pneumatic systems.

bleed-off circuit

A flow-control configuration in which the flow control valve exhausts air when actuated. In a bleed-off circuit, the flow control valve can be located anywhere along the main line.

blow-off pressure

The point at which the internal pressure of a pneumatic system triggers a relief valve. Blow-off pressure is also called cracking pressure.

cam-operated directional control valve

A type of directional control valve that actuates using the distinct physical geometry of a cam. In cam-operated directional valves, cam rotation actuates the valving mechanism of the valve.

check valve

A type of directional control valve that allows air to flow in only one direction. Check valves include in-line check valves and right-angle check valves.

check valves

A type of directional control valve that allows air to flow in only one direction. Check valves include in-line check valves and right-angle check valves.

compressed

To be squeezed or pressed together into a smaller space. Compressed air is used by pneumatic systems to do work.

compressor

A component that pressurizes ambient air. Compressors direct air into a pneumatic system after pressurizing it.

cracking pressure

The point at which the internal pressure of a pneumatic system triggers a relief valve. Cracking pressure is also called blow-off pressure.

cylinder

A type of linear actuator that uses a piston to produce motion in a straight line. Cylinders physically contact a valving element to change its position during mechanical actuation.

diaphragm

A spring-loaded valve mechanism that moves in response to variations in pressure in a pneumatic system. The diaphragm is a flexible membrane that responds to changes in pressure and moves the poppet.

diaphragm-type regulating valve

A type of pneumatic regulating valve with a spring-tensioned diaphragm as the main valving element. In a diaphragm-type regulating valve, air pushes against the diaphragm, a poppet closes the inlet to the valve, and as air pressure against the diaphragm decreases, the poppet opens the inlet.

diaphragm-type regulating valves

A type of pneumatic regulating valve with a spring-tensioned diaphragm as the main valving element. In a diaphragm-type regulating valve, as air pushes against the diaphragm, a poppet closes the inlet to the valve, and as air pressure against the diaphragm decreases, the poppet opens the inlet.

directional control valve

A fluid system component that determines the path air takes in a pneumatic system. Directional control valves are used to move actuators into various positions.

direct-operated

A type of check valve. Direct-operated valves are actuated by compressed air pressing directly on the valving element.

electrical actuation

The act of tripping or seating a valving element using an electrical device, such as a solenoid. Electrical actuation allows automated or remote-controlled valve operation.

exhaust port

The port in a valve that allows excess pressure to escape. Exhaust ports are often covered by a ball attached to a spring that seals the port until excess pressure triggers the ball to unseal the port and allow the pressure to be released into the atmosphere.

flow

The directional movement of air in a pneumatic system. Flow causes an actuator to move and perform work.

flow control valve

A fluid system component that controls the rate of air flow. Flow control valves make it possible to control the speed of the actuator.

flow rate

A specification of a compressor that indicates how much air a compressor can move in a certain amount of time. Flow rate for pneumatic pumps is measured in cubic feet per minute, or cubic meters per minute.

four-way valve

A directional control valve. A four-way valve is typically used for double-acting actuators.

gripper

A double-acting linear actuator. A gripper has the capability to repeatedly clamp and release.

inlet port

An opening on the side of a compressor. The inlet port draws fluid into the system.

in-line

A type of check valve that has the inlet and outlet ports located directly opposite each other. In in-line check valves, air flows through the valve in a straight line.

kilopascal

A unit used to measure pressure in the SI system, abbreviated as kPa. Kilopascal is a measurement used to determine operating pressure in a pneumatic system.

limit switch

A mechanical switch that halts further motion of the object that triggered the switch. A limit switch allows operators to remotely control an actuator.

lunging

A situation in which the actuator and the load are moving in the same direction. Lunging, or overrunning, often causes an actuator to jump suddenly.

manual actuation

The act of tripping or seating a valving element by hand. Manual actuation uses handles or cranks.

mechanical actuation

The act of tripping or seating a valving element using the physical movement of machine components. Mechanical actuation employs a device, such as a plunger or cylinder.

meter-in circuit

A flow-control configuration in which the flow control valve is located between the actuator and the compressor. Meter-in circuits control the amount of flow to the actuator.

meter-out circuit

A flow-control configuration in which the flow control valve is located at the outlet of the actuator. Meter-out circuits control the amount of fluid leaving the actuator.

needle valve

A type of flow control valve that adjusts the flow of air between and including fully on and fully off. Needle valves consist of a sharp conical obstruction that extends or retracts to block or allow flow.

one-way valve

A directional control valve that allows air to move in only one direction. One-way valves are most commonly check valves with a ball-type poppet.

operating pressure

The amount of pressure nearest the point of performing work at the output end of a fluid system. The operating pressure is used to specify the capability of valves and actuators.

overpressure

A situation in which the pressure in a pneumatic system exceeds manufacturer recommended levels. Overpressure can lead to equipment damage and personal injury but can be controlled by a relief valve.

override

A means of bypassing the essential function of a device, such as a valve. Overrides exist for various exceptions that can occur during normal operation.

pilot port

A type of valve port. In a pilot port, the compressed air travels when actuating the pilot portion of a pilot-operated valve.

pilot signal

A surge of fluid through the pilot port. Pilot signals actuate the pilot portion of a pilot-operated check valve.

piloted-operated check valve

A type of check valve that has an additional port for a pressure signal. Pilot-operated check valves allow operators to override normal check valve operation.

pilot-operated

A type of check valve. Pilot-operated check valves are actuated by compressed air coming from a pilot or ancillary port for the purpose of overriding a valve.

pilot-to-close check valve

A type of check valve. Pilot-to-close check valves allow fluid to flow in the forward direction and stop flow in the reverse direction under normal circumstances.

pilot-to-open check valve

A type of check valve. Pilot-to-open check valves allow fluid to flow in the reverse direction by opening the poppet when needed.

piston

A rod inside a cylinder that is moved by pneumatic pressure. A piston is contained by a cylinder.

piston-type regulating valve

A pneumatic regulating valve with a spring-tensioned, cup-shaped piston as the main valving element. In a piston-type regulating valve, air pressure from the inlet and pressure from the piston act against each other, allowing only a predetermined level of pressure to leave the valve.

piston-type regulating valves

A pneumatic regulating valve with a spring-tensioned, cup-shaped piston as the main valving element. In a piston-type regulating valve, air pressure from the inlet and pressure from the piston act against each other, allowing only a predetermined level of pressure to leave the valve.

pneumatic actuation

The act of tripping or seating a valving element using compressed air. Pneumatic actuation trips a valve when a valving element detects a lack of air pressure.

pneumatic system

A power transmission system that uses the force of flowing gases to transmit power. Pneumatic systems most commonly use air to transmit power.

poppet

A valve mechanism that continually opens and closes in response to variations in pressure. The poppet is attached to a spring-loaded diaphragm.

ports

An opening on a valve through which fluid can flow; can also be called ways. Ports allow air into and out of a pneumatic system.

positions

The number of physical settings on a directional control valve. Valves can have two or more positions.

pounds per square inch

psi. An English system unit of pressure. Pounds per square inch measures the amount of force that is applied over an area of one square inch.

power

The rate at which work is accomplished. Power is expressed in foot-pounds (ft-lb) or newton-meters (N-m) and is the result of the amount of work accomplished divided by the time it took to do the work.

pressure differential

The pressure from a load on an actuator minus the cracking pressure of a valve. Pressure differential is also called pressure drop and represents the difference between two pressure levels.

pressure drop

The pressure from a load on an actuator minus the cracking pressure of a valve. Pressure drop is also called pressure differential and represents the difference between two pressure levels.

pressure switch

A mechanism that regulates pressure in an air receiver. Pressure switches are actuated by a change in pressure.

programmable logic control

PLC. A processor-driven device that uses logic-based software to provide electrical control to machines. Programmable logic control can electrically activate directional control valves.

regulating valve

A pneumatic power device that protects the system against overpressure. Regulating valves are sometimes called reducing valves.

regulating valves

A pneumatic power device that protects the system against overpressure. Regulating valves are sometimes called air regulating valves or reducing valves.

relief valve

A component that allows pressurized air to escape a pneumatic system when the system pressure reaches a critical pressure. Relief valves prevent excess pressure from damaging a pneumatic system or causing bodily injury.

resistance

The opposition to a force. Resistance can include a variety of factors, such as the weight of a load or friction during movement.

right-angle check valve

A type of check valve that has the inlet and outlet located at right angles to each other. Right-angle check valves have a higher flow capacity than in-line check valves.

sequence valve

A pneumatic valve that allows air into a secondary system. Sequence valves activate after a set pressure is reached.

solenoid

A coil of wire that generates an electromagnetic force when a current is applied. When activated, solenoids can open and close valves.

spool

A valve that controls the direction of pneumatic flow. A spool valve consists of a cylindrical spool that alternately blocks and opens channels in the pneumatic system.

spring

A device that yields under a compressive force and returns to its original shape once the force is removed. A spring is used as part of the sealing element in a regulating valve.

tapered head

A head of a valve that gradually changes diameters. Tapered heads are found on needle valves.

threaded plunger

The base of a needle valve that allows the valve to be screwed or unscrewed to adjust the opening. Needle valves are controlled manually.

three-way valve

A directional control valve. A three-way valve diverts flow between two possible paths.

two-way valve

A type of directional control valve with two ports: one inlet and one outlet. Two-way valves do not have an exhaust and usually only allow fluid to flow in one direction.

valves

A mechanical device that controls air in a pneumatic system. Valves include two-, three-, and four-way directional valves.

ways

An opening on a valve through which fluid can flow; can also be called ports. Ways allow air into and out of a pneumatic system.

work

The result of a force applied to an object and the distance through which the force is applied. In an equation, work is force multiplied by distance.

working pressure

The pressure rating that indicates the maximum pressure a conductor should experience in service. Working pressure is often called maximum allowable working pressure (MAWP).