My definition of compressed air control valve actuators is that they are the devices that operate an air valve and the person that actuates the air valve using the valve actuator is the operator. My definition, but it works for me. Need to know a lot more about air valve actuators? These pages have it all. Read on.
Not everyone uses this same valve terminology as a norm, so when you are talking to other folks about compressed air components, in particular air valves, make sure they define their terms to help you better understand, and for your mutual understanding. Misunderstood valve or air component names is an ongoing problem.
So, 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.
Multiple 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 a particular valve is not in use, it is the internal spring actuator that returns that valve to its un-actuated, resting state. A valve at rest is one that is not being acted upon by an external force or external actuator.
The actuator that an operator uses to operate an air 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 (See site map under valves ) for purposes of simplicity all of the schematics show those valves without any actuators.
Here are some those valve drawings with a valve actuator, or valve actuators, added.
Fig 41 shows a 3/2 valve with an internal spring actuator,drawn on the right side of the schematic.
It is customary to draw an air valve with the internal valve actuator shown 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 is the position that valve will be in its 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 incoming 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 flow path through the valve will be opened, and the exhaust port will be blocked. The drawing depicts both sides of the valve, but both sides of the schematic are the same valve. One side shows the flow path through the valve if it has been shifted in one position, and the other side shows the flow paths when that same valve is shifted into its second position.
In this case, as long as air is present at the air signal port of the valve, the valve will remain shifted, and air will continue to flow through the valve to the air-using 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 cannot be seen). Since I took the photo of the valve, I know that this one has 2 positions, but that cannot be determined by looking at the outside of an air valve. This one is a single air piloted, spring return 3/2 NC air valve, to be precise. It is typical for an air valve to have a label which shows a schematic identifying the flow paths of that valve.
What is controlling the valve in Fig 43 is the internal spring actuator 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.
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 another air pilot end cap attached to the other 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 change, but would stay in its last position until such time as another air pilot signal reached the other air port, to then shift the valve back.
Solenoid Valve Actuators
A solenoid, in terms of compressed air valves, is a device that allows the actuation of the air valve using an electrical signal, or the combination of an electrical signal and a compressed air signal to accomplish valve actuation.
When an air valve is actuated solely by the electrical signal, that solenoid valve is defined as being direct acting.
When a solenoid valve uses both electricity and compressed air to shift that air valve, that type is deemed a solenoid pilot valve.
Fig. 44 shows a double solenoid pilot operated air valve.
A compressed air circuit may be controlled entirely by electricity, and all the compressed air valves, the proximity switches, temperature sensors, E-stops, they all can receive signals from, and in many cases send signals back to the brain of the air circuit, the PLC. (Programmable Logic Controller)
When the solenoid valve actuator gets an incoming electrical signal, and assuming that the valve is in good shape, then the valve will shift and air will flow to the application.
Solenoid actuators usually come from the factory already attached to their air valve. To power the solenoids, it is necessary to bring a power supply to each of the solenoid valve actuators either directly or through a PLC driven relay.
DIN Connectors On Valve Actuators
One way to accomplish this electrical hookup is through the use of DIN type electrical connectors , the type shown in Fig. 44.
Rather than hard wiring directly to the air valve, and having to undo the wiring each time the valve is disconnected from the air circuit, the hard wiring need only go to the DIN connector cap once. Then, it is the DIN that is connected to the solenoid via an internal plug. Using a DIN connector allows the non-electrical-skilled maintenance person to disconnect and re-connect the wiring to the valve quickly and safely when that valve needs to be changed out.
Lighted DIN Connectors
If buying DIN connectors, do purchase ones that contain an LED. The LED will light up when the valve solenoid is energized. Operators can then tell at a glance if power is getting to that solenoid. If the valve is not working, the operator can be sure that power is getting to the DIN. Therefore, it is either the valve that has failed, or perhaps a piece of air equipment downstream from that valve is not operating, and it is manifested by the appearance of a non-shifting valve. With a lighted DIN there will be less time consumed tracking the problem.
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