Pneumatic valves are one of an array of components

responsible for controlling the pressure, rate, and amount of air as it moves through a

pneumatic system. Pneumatic systems, which depend on the force of compressed air to transmit

power, can be found in countless industrial flow control applications, from pneumatically

operated power tools to diesel engines. Based on other components within a given application

and the type of pneumatic system used, one of several types of pneumatic

control components valves may be found

at the heart of the device.

This article will review the common types of pneumatic valves that are used in the

industry and provide information on the configurations and key specifications associated with

these devices. To learn more about other types of valves, see our related guide on the types

of valves. For an understanding of pneumatic actuators, see our guide all about pneumatic

actuators.

Pneumatic Valve Use Context

The term “pneumatic valve” generally has two distinct contexts of use which require

some explanation. In the first context, a pneumatic control valve is a device that is used to

control or modulate the flow of air (or another inert gas) in a pneumatic system. They do so

by controlling the air or gas at the source, regulating its passage as needed into tubing,

pipes, or devices in an automated pneumatic system. The actuation component that causes the

pneumatic valve to open or close might be accomplished in any of several ways, including

manually, electrically via a solenoid valves or motorized actuator, or pneumatically. The key concept to note

in this case is that it is pressurized air or gas that is being controlled and which is

flowing through the valve ports in the pneumatic system.

In the second context, air is being used as the control mechanism on the valve, but the

media that is flowing through the valve ports is something other than air, perhaps water,

oil, or some other fluid. In this context, the pneumatic air valve is functioning to provide

flow control in a valve, but the fluid being controlled is not air. The air is serving as the

control media, being passed through a pneumatic actuator to open, close, or modulate flow as

needed. These valves are therefore sometimes referred to as pneumatically-actuated valves.

To summarize, in the first context, air is being controlled but may or may not be driving

the control mechanism of the valve. In the second context, something other than air is being

controlled but the control mechanism is air.  A distinction between these two general

contexts will help with a further understanding of pneumatic valves and their uses. The types

of pneumatic valves below are generally representative of the first context.

Types of Pneumatic Valves

Pneumatic valves, also called directional control valves, may be classified using several

different approaches which include:

the number of entry and exit ports they possess

the number of flow paths or switching positions that are available

the mechanism that is used to open or close the ports

the position the valve is in when in the un-actuated state

Functional directional control valves, those that control the direction of air flow or

inhibit flow all together, are a large class of pneumatic valves that houses multiple

variants. These devices can be used in various ways in a hydraulic system, such as to connect

or disconnect the main compressed air supply from the system or to advance or retract air

compact cylinders

that move as part of the machine or process for which the

pneumatic actuator system has been

created.

With this in mind, we can broadly delineate the primary types of pneumatic valves as:

Two-Way directional control pneumatic valves

Three-Way directional control pneumatic valves

Four-Way directional control pneumatic valves

Spring offset pneumatic valves

Two-Way Directional Control Pneumatic Valves

A two-way directional valve passes air in two directions, through two ports which can be

open or closed. If the valve ports are closed no air can flow through the valve. If the ports

are open, air may move from the first port through the valve and through the second port or

in the opposite direction.

Three-Way Directional Control Pneumatic Valves

A directional three-way air control valve has three ports, each of which serves a

different purpose. The first port is used to connect the valve to an actuator or another

device. The second port is connected to an airflow. The third port is used as an exhaust

exit. When the first and second ports are open and the third is closed, air moves through the

valve to the device. When the first and third ports are open and the second port is closed,

the actuator can vent exhaust.  Three-way valves are often connected to actuators in

cylinders or used in pairs and connected to double-acting

pin cylinders.

Four-Way Directional Control Pneumatic Valves

A four-way directional valve has four distinct ports, two of which connect to actuators,

one that connects to a pressurized airflow, and one that serves as an exhaust pathway. They

are among the most common types of valves found in pneumatic systems because the four

distinct paths allow the valve to effectively reverse the motion of a motor or basic

clamp cylinders. An

additional port is sometimes added to a four-way valve, making it a five-ported four-way

valve. A four-way valve with an additional port is often used to provide dual pressure,

meaning the valve can apply one of two kinds of pressure and alternate between the two

depending on what the application requires. Alternatively, the valve can use the other port

as a secondary exhaust port.

Spring Offset Pneumatic Valves

This type of pneumatic valve classification refers to the manner in which air flow

direction is switched. For example, in a two-way directional valve, the valve is either open

(air flow is enabled) or closed (air flow is prevented). In order for each port to assume an

open or closed position, an actuator moves a valve spool into position. To release the valve

spool and return the pneumatic valve to its previous position, a spring releases the spool. A

two-way directional valve that functions in this manner is also called a spring offset valve.

Pneumatic Valve Designations and Configurations

Within the broad classification of pneumatic valves such as two-way, three-way, and

four-way, there are various combinations of valve configurations that reflect the parameters

identified earlier – namely ports, switching positions, and non-actuated state (its default

open or closed position). When defining these configurations, a standardized numbering system

is typically used that includes two numbers separated by a slash (/). The first number is the

number of ports in the valve and the second number reflects the number of switching

positions.

For example, a 2/2-way pneumatic valve is a valve that has two switching positions and

two ports. A 3/2-way valve is a two position valve with three ports. By extension, a 4/2-way

valve represents a valve that has two switching positions and four ports; a 5/2-way valve has

two switching positions and five ports.

Within these options, there is also the question of the non-actuated state, which relates

to flow control. A 2/2-way valve could be available in a normally closed position, meaning

that when it is un-actuated, the valve is closed and does not allow the flow of air between

the ports. To open the valve, actuation is needed.

In a normally open valve, the opposite is true – without actuation, the valve allows air

flow, requiring actuation to close off the valve.

In three-way valves, one port is always open. In such cases, a closed resting state

usually results in blocking the air-flow port, so air isn’t moving unless the device is

turned on. As an example, a five-port three-position valve may have port 1 as its pressure

inlet, ports 2 & 4 as work ports, and ports 3 & 5 as exhaust ports.

Configurations for pneumatic valves that are commonly used include 5/3, 5/2, 4/2, 3/2,

and 2/2.

Pneumatic valves can be spring offset or detented.

In spring-offset valves (as described above), the valve will return to the starting state or

condition when any actuation is removed. In detented valves, the valve will remain in the

last activated position until it is switched again by the operator.

Pneumatic Valve Specifications

There are specifications for pneumatic valves, some key ones of which are summarized

below. These parameters are for general guidance and the reader should know that individual

valve manufacturers and suppliers may characterize their valves differently. Furthermore, the

exact specifications will depend on several factors such as the manifold design, desired

porting, and actuation mechanism for the valve.

Operating pressure or pressure range – the amount of pressure or range of pressures (for

example in psi, Bars, or Pa) which the valve is rated to handle.

Operating medium – the types of media that the valve can safely control. In most cases,

this will be compressed air.

Flow capacity or flow coefficient  – a measure of the capacity of the valve to move

or flow air through it, with the flow coefficient (Cv) representing the proportionality

constant between the flow rate and the differential pressure.

Cycle rate – the maximum number of valve cycles at which the valve can operate per unit

of time.

Response time – the amount of time required for the valve to switch states or positions

once actuated.

Port size – the physical dimensional parameters that define the port sizes on the valve

and the thread style.

Coil rated voltage – for electrically actuated valves, a measure of the maximum voltage

that can be sustained by the actuation coil and may be rated in DC and AC volts.

Summary

This article presented a review of the common types of pneumatic valves, their

configurations, and the key specifications that define these valves. For information on other

topics, consult our additional guides or visit the Thomas Supplier Discovery Platform where

you can locate potential sources of supply for over 70,000 different product and service

categories.

Sources:

http://ingersollrand.jp

https://www.ekci.com/

https://www.ipolymer.com/blog/common-pneumatic-valve-types-for-engineers/

https://www.machinedesign.com/mechanical-motion-systems/pneumatics/article/21834670/the-

basics-of-pneumatic-control-valves

https://tameson.com/52-way-and-42-way-pneumatic-valve.html