FAQs

Frequently Asked Questions: Pneumatic Basics

What is closed cross-over and why is it an advantage?
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A closed cross-over valve features a stem and poppet that work in conjunction with one another ensuring that the poppet seals the exhaust port before the valve opens to flow. There is no transitional state from one function to the next providing the operator precise control between positions.

What is a 2-way valve?
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A 2-way directional control valve provides on / off function. Actuating the valve allows air to flow through the input port and out the output port. View a 2-way normally closed valve cross section.

What is a 3-way valve?
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A 3-way directional control valve pressurizes and exhausts a port. When a 3-way normally closed valve is actuated, air flows through the input port and out the output port. In the unactuated position, air flow travels from the output port through the exhaust port. View a 3-way valve cross section.

What is a 4-way valve?
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A 4-way directional control valve pressurizes and exhausts two ports (the valve body consists of 5 ports). A 4-way valve has four distinct flow paths within the valve and is commonly used to cause reversible motion of a cylinder or motor. Actuating the valve directs flow through input port 1 to output port 4 as output port 2 exhausts through port 3. In the unactuated position, air flow is directed through input port 1 to output port 2 as output port 4 exhausts through port 5. View a 4-way valve cross section.

What is normally open?
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Often referred to as normally passing, air flows from the input port to the output port in the unactuated position.

What is normally closed?
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Often referred to as normally not passing, air flow is blocked at the input port in the unactuated position.

What is a shuttle valve?
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Shuttle valves are used when a signal is required to be selected from two or more different sources. Also known as "OR" valves, they allow a signal to pass through from either input A or B (or both) and will allow the reverse flow of system exhaust through these same inputs. A shuttle valve selects the higher of two pressures, a function that is to be considered when designing circuitry. View a shuttle valve cross section.

What is an "AND" valve?
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"AND" valves are used in circuit control applications that require a combination of inputs to produce a single output. When a signal is supplied to both input ports 1 and 2, the output flows from port 2. The output flow will always be the lower of the two pressures. Both input pressures are required to receive an output signal from the valve (loss of input will cancel the output signal). View an AND valve cross section.

What is an "OR" valve?
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"OR" valves are commonly known as Shuttle valves.

What is the difference between a flow control and a needle valve?
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Although the basic function is flow restriction, the fundamental difference between the two is the needle valve controls flow in both directions (bi-directional) and the flow control valve controls flow in only one direction, allowing free flow in the opposite direction.

What is meter in?
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Controlled flow is from port 2 to port 1, whereas, free flow is from port 1 to port 2. Pneumadyne's reverse flow control valves are meter in.

What is meter out?
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Controlled flow is from port 1 to port 2, whereas, free flow is from port 2 to port 1. Pneumadyne's standard flow control valves are meter out.

What is a directional control valve?
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The basic pneumatic valve is a mechanical device consisting of a body and a moving part (poppet or stem), which connects or disconnects passages within the body. 2-way, 3-way and 4-way valves are directional control valves.

What is a circuit control valve?
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Circuit control valves are used to control flow volumes and pressures within a system. Shuttle valves, check valves, flow controls, needle valves, quick exhausts and pressure regulators are considered circuit control valves.
What is a quick exhaust valve?
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Air quick exhaust valves are commonly used to allow rapid cylinder return without permitting air to travel back through the pneumatic system. As pressure is applied to the input port, an internal mechanism is shifted to block the exhaust port and allow flow through the output port. When pressure is removed from the input port, back flow at the output port unseats the internal mechanism and allows flow through the exhaust port.

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