Switch and Valve Concepts Used in Fluid Power

Pneumatic valves used in fluid power
(ASCO Numatics)

The direction in which a cylinder piston will move or a fluid motor will rotate can be controlled by the direction of flow into the device. A cylinder is said to reciprocate if it's piston travels back and forth being reversed automatically at each end of its stroke without human operator attention. In an air cylinder, automatic reciprocation can be stopped by an electrical action or by a shutoff valve in the airline. If stopped by electrical action it will continue to travel until it reaches one end or the other of its stroke. If stopped by shutting off the air, it can be made to stop anywhere in its stroke.

Cylinders and Actuators
(ASCO Numatics)

Fluid valves are typically described as being either in the open or closed position. As described, the open position allows the flow of fluid, while the closed position prevents flow. The normal position of the valve is defined as the position of the valve when its spool is unshifted and the power is off. This means that any mechanical actuators, such as springs, are in their non-actuated positions. Electrical actuators, such as solenoids, are powered off. 

The normal position can sometimes be referred to as the unshifted, de-energized, or unactivated position. Valves that do not have mechanical or electrical actuators do not have a normal position because they must be manually moved. When shifted they remain in that state until manually shifted to another position. The terms normally opened and normally closed are used to describe the condition of a valve when it is in the normal position.

Watch the video below for a better understanding of these concepts.

For more information on fluid power components, or on fluid systems, contact Process Control Solutions by visiting https://processcontrolsolutions.com or calling (800) 462-5769.