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Pneumatic Control Valves 235

Hydraulics and Pneumatics Department

Class Information

Tooling U classes are offered at the beginner, intermediate, and advanced levels.
The typical class consists of 12 to 25 lessons and typically requires at least two hours of instruction time.

Class Name	Pneumatic Control Valves 235
Description	This class surveys the most common types of pneumatic control valves and explains how each type functions within a pneumatic system.
Prerequisites	570100 570125
Difficulty	Intermediate
Number of Lessons	16

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Class Outline

Class Objectives

Objectives

Pneumatic Control

Types of Pneumatic Valves

Air Regulating Valves

Diaphragm-Type Regulating Valves

Piston-Type Regulating Valves

Pneumatic Relief Valves

Directional Control Valves

Three- and Four-Way Valves

Check Valves

Pilot-Operated Check Valves

Directional Control Valve Actuation

Flow Control Valves

Flow Control Configurations

Sequence Valves

Summary

Describe pneumatic valves.

Identify the types of pneumatic valves.

Describe air regulating valves.

Identify the parts of a diaphragm-type regulating valve.

Describe a piston-type regulating valve.

Describe a pneumatic relief valve.

Describe a directional control valve.

Identify three- and four-way valves.

Identify a check valve.

Describe a pilot-operated check valve.

Distinguish between methods of directional valve actuation.

Describe the operation of a flow control valve.

Describe different flow control configurations.

Describe a sequence valve.

Class Vocabulary

Term	Definition
2/2 valve	A directional control valve with two ways, two ports, and two positions.
3/2 valve	A directional control valve with three ways, three ports, and two positions.
4/2 valve	A directional control valve with four ways, four ports, and two positions.
4/3 valve	A directional control valve with four ways, four ports, and three positions.
air-piloted directional control valve	A directional control valve that is actuated by compressed air coming from the pilot port.
bleed-off circuit	A flow control configuration in which a valve exhausts air when actuated. The valve of the bleed-off circuit can be located anywhere along the main line.
cam-operated directional control valve	A directional control valve that is actuated by the distinct physical geometry of a cam. As the cam rotates, its shape actuates the valving mechanism of the valve.
check valve	A control valve that allows air to flow in only one direction. Check valves prevent backflow.
cracking pressure	The point at which the internal pressure of a pneumatic system triggers a valve. Also called the blow-off pressure.
detent	A linear or rotary device with fixed points of resistance. Each point of a detent represents a distinct phase of valve 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 pneumatic regulating valve with a spring-tensioned diaphragm as the main valving element. 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 component that determines the path air takes in a pneumatic system. Directional control valves are used to move actuators into various positions.
direct-operated	Actuated by compressed air pressing directly on the valving element.
electrical actuation	The act of tripping or seating a valving element with an electrical device such as a solenoid.
filter	A screen used for trapping very fine and fine particulate matter.
flow control valve	A fluid component that controls the rate of air flow. Flow control valves make it possible to control other system variables like the speed of an actuator.
four-way valve	A directional control valve typically used for double-acting actuators.
FRL	A device that conditions air for use in pneumatic systems. An FRL is a combination filter-regulator-lubricator.
full line pressure	The maximum pressure that a line can withstand during operation.
full-flow pressure	The point at which a relief valve is diverting air at its maximum rate.
gripper	A double-acting linear actuator that has the capability to repeatedly clamp and release.
hydraulic actuation	The act of tripping or seating a valving element with pressurized liquid.
hysteresis	The tendency of the postion of a component to be dependent on the previous position of the component when reacting to a physical stimulus. Hysteresis leads to varying degrees of inaccuracy relative to valve actuation and target pressure.
infinite positioning	Characterized by being fully on, fully off, or anywhere in between. Infinite positioning allows any range of possible positions.
in-line check valve	A check valve with the inlet and outlet located directly opposite each other.
limit switch	A device used for making, breaking, or for changing the connections in an electric circuit.
lubricator	A component that releases an oil mist into certain portions of a pneumatic system to lubricate moving parts.
lunging	A situation in which the actuator and the load are moving in the same direction. Lunging, or overrunning, often causes the actuator to suddenly jump.
manual actuation	The act of tripping or seating a valving element by hand.
master control valve	A directional control valve that directs air to different areas of the pneumatic system.
mechanical actuation	The act of tripping or seating a valving element through the intervention of a mechanical device such as a plunger or cylinder.
meter-in circuit	A flow control configuration in which the valve is located between the compressor and the actuator.
metering valve	A valve with infinite positioning and variable control that is capable of regulating the flow of fluid. A needle valve is a type of metering valve.
meter-out circuit	A flow control configuration in which the valve is located at the outlet of the actuator.
muffler	A pneumatic component that decreases harmful noise by slowing air as it is exhausted from a pneumatic system.
needle valve	A valve that adjusts the flow of air between and including fully on and fully off. The needle valve consists of a sharp conical obstruction that is extended or retracted to block or allow flow.
normally closed position	A valve position in which the valving element is unactuated and covering a port. A normally closed valve opens when it actuates.
OSHA	The Occupational Safety and Health Administration. A government agency under the U.S. Dept. of Labor that helps employers reduce injuries, illnesses, and deaths in the workplace.
outstroke	The motion of the cylinder piston as it extends. Some flow controls are best located downstream of the outstroke in order to regulate the speed of the cylinder.
overpressure	A situation in which the pressure in a pneumatic system has exceeded recommended levels. Overpressure can lead to equipment damage and personal injury.
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	The port through which compressed air travels when actuating the pilot portion of a pilot operated valve.
pilot-operated	Actuated by compressed air coming from a pilot or ancillary port for the purpose of overriding a valve.
pilot-operated check valve	A check valve that is direct-operated under normal circumstances and actuated by a pilot signal under circumstances that call for a valve override.
pilot-to-close check valve	A check valve that allows flow in the forward direction and stops flow in the reverse direction under normal circumstances. The pilot port stops flow in either direction by closing the poppet when needed.
pilot-to-open check valve	A check valve that allows flow in the forward direction and stops flow in the reverse direction under normal circumstances. The pilot port allows flow in the reverse direction by opening the poppet when needed.
piston-type regulating valve	A pneumatic regulating valve with a spring-tensioned, cup-shaped piston as the main valving element. 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.
PLC	A processor-driven device that uses logic-based software to provide electrical control to machines.
pneumatic actuation	The act of tripping or seating a valving element with compressed air.
poppet	A conical valving element that continually opens and closes in response to variations in pressure.
port	An opening on a valve through which fluid can flow.
position	The number of physical settings on a directional control valve. A three-position valve can be placed in three different physical settings with a control such as a lever.
pressure differential	The difference between two levels of pressure in a pneumatic system. Since high pressure moves toward low pressure, a pressure differential causes pneumatic flow.
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 override	The full-flow pressure minus the cracking pressure. The pressure override is a measure of the increase in pressure over the cracking pressure when additional flow passes through the valve after it cracks.
pressure port	A valve inlet port closest to the pump.
reducing valve	A pneumatic power device that protects the pneumatic system against overpressure. Reducing valves are sometimes called air regulating or regulating valves.
regulating valve	A pneumatic power device that protects the pneumatic system against overpressure. Regulating valves are sometimes called air regulating valves or reducing valves.
relief valve	A component that exhausts air into the environment once a pneumatic system reaches a critical pressure, beyond which damage or injury can occur.
right angle check valve	A check valve with the inlet and outlet located at right angles of each other.
rotary valve	A directional control valve that directs the flow of fluid when turned.
sequence valve	A pneumatic valve that actuates and allows air into a secondary system after a critical 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.
speed of sound	The speed at which sound moves through air. At normal elevation and at 70° F (21° C), the speed of sound is 770 mph (344 m/s).
spool	A cylindrical valving element that alternately allows and blocks flow depending on its linear position.
three-way valve	A directional control valve that diverts flow between two possible paths. Three-way valves allow flow from the pressure port to two other ports.
two-way valve	A valve with one inlet pressure port that services one of two possible outlets, depending on the position of the valve.
valve	A mechanical device that controls air in a pneumatic system. Valves are responsible primarily for the proper control of a pneumatic system.
valving element	The component of a valve that covers a port. Depending on the design of the valve, the valving element controls direction, pressure, or flow by opening and closing.
way	A characteristic of a valve that indicates how a fluid can flow through it.