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.
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