Valve Actuators; what operates your air valve?

Valve actuators; when I’m writing about compressed air I always refer to the device that operates an air valve as a valve actuator. Or, just as an actuator when that specific page is primarily focused on air valves.

If I’m talking about a linear device, I’ll use the term Air Actuator or air cylinder.

Not everyone uses this same valve terminology as a norm, so when you are talking to other folks about compressed air components, make sure they define their terms to help your mutual understanding.

When I’m writing about air valves and I refer to the operator, the operator is the person that moves the valve lever, pushes the valve button or flicks the switch to actuate the valve. An operator will actuate the valve using the valve actuators.

Most compressed air valves will have at least two actuators.

One is usually installed inside the valve, is usually a spring, and I call this the internal valve actuator. When the external valve actuator for that valve is not in use, the internal spring returns that valve to it's unactuated, resting state. A valve at rest is one that is not being acted upon by an external force or external actuator.

The actuator that the operator uses to operate the valve is what I call an external valve actuator. It can be a solenoid, a lever, a push button, a mechanical switch of some sort, an air signal, and all of these external actuators come in a variety of shapes and sizes depending on the manufacturer and the valve.

In the instruction pages on how to draw air valves,

Now let’s look at some valve drawings with a valve actuator, or valve actuators, present.







Fig 41 shows a 3/2 valve with a spring valve actuator which is drawn on the right side of the schematic.

It is customary to draw an air valve with the single internal valve actuator on the right, and, if the valve is at rest, to show the air supply on the right side of the valve drawing as shown in Fig 41.

Drawn in this fashion, the valve shown is a 3/2 NC (normally closed) valve. When the valve is at rest, the internal spring is in control, and the valve is not passing compressed air through it.

Regardless of the type of valve actuator that might be drawn on the left, if the air supply is shown on the spring side, then that's the position that valve will be in it's resting state.

Air Pilot Valve Actuators

Fig 42 shows the same 3/2 valve with the internal spring actuator shown on the right, and on the left side, a dashed line drawn at the midpoint of the box, tangential to the valve body.

The dashed line is the generally accepted symbol for an air pilot signal .

When an air pilot signal arrives at the air signal port of the compressed air valve, the valve internal air seal (a poppet or a spool type) is shifted by the signal air compressing the spring as it shifts the valve innards.

In Fig 42, you can see that if the valve is shifted by the air pilot signal air, the the flow path through the valve will be opened to the application, and the exhaust port will be blocked. Remember, both ‘sides’ of the valve schematic are the same valve. One side shows the flow path through the valve if it’s in one position, and the other side shows the flow paths when that same valve is shifted.







In this case, as long as air is present at the air signal port of the valve, it will remain shifted, and air will flow through the valve to the application.

When the air pilot signal is dropped, and the air pilot signal line loses pressure, the valve internal spring actuator once again takes over control of the valve, shifting the internal spool or poppet back. The supply of air to the application is blocked, and air from the application can now exit through the valve to the exhaust port and to atmosphere.

Fig 43 is a photo of a 3/2 valve, with 3 "working" ports (one on the bottom can't be seen). I know that it has 2 positions, but that can't be determined by looking at the outside of a valve. This one is a "single air piloted, spring return 3/2 NC air valve", to be precise.

What is controlling the valve in Fig 43 is the "internal" spring located under the thin cap on the left end of the valve. The wide cap on the right contains the air port for the air pilot signal.

Of course, should the air circuit require it, this same valve could have double air pilot valve actuators, with the omission of the internal spring actuator, and an air pilot end cap on each end.

This double air pilot controlled air valve can be used as a “latching” valve in air circuits. When an air pilot signal reached one of the end ports the valve would shift. Even if that air pilot signal was dropped, the valve internals, and hence the compressed air path through that valve, would not shift, but would stay in position until such time as another air pilot signal reached the other air port, to then shift the valve back.


Please click here for more on compressed air valve actuators!







Here's more info on compressors in general valve actuators.

To top