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Solenoid Actuator;
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There are a host of ways to operate compressed air valves; manual levers, push buttons, palm buttons, roller cams, whisker switches...many others including solenoid actuators.
When I write about the various methods to actuate an air valve I use the term actuator for the mechanical device that shifts the internal workings of the air valve, and I use the term operator for the person that moves the lever or pushes the button to actuate the valve.
Please click here for more general information on compressed air valves themselves.
There are two kinds of solenoid actuators for air valves. One is covered here on this page, the Direct Acting Solenoid Operator and the other will be covered on this page Air Pilot Solenoid Operators.
Quick Definition of a Solenoid
As it relates to compressed air valves, a solenoid is a device that, when energized with electricity, creates a magnet inside itself that moves something.
Depending on the type of air valve, the item that moves could be a device to control air flow through the valve, or a device to control air flow within the solenoid to do work. More on this later.
Direct Acting Solenoid Actuator
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In the drawing above, #1 is the coil itself, and inside the black exterior are the actual coil windings, depicted by the gold color.
Item #2 is the depiction of the compressed air supply to the valve, in this case a 2/2 normally closed air valve.
Note how the compressed air (depicted in blue) enters the valve through the supply port, but is blocked from flowing by a poppet (purple color) that is sitting on an "O" ring, sealing the incoming air from flowing through the valve.
The coil is de-energized, and the internal valve actuator, the spring, is in control at this time.
The solenoid coil, when it's energized, will form a magnetic field which will move the pole piece (#3 - brown color) inside the coil housing. In this example, the pole piece will move to the right. Since it's attached to the poppet, when the coil is energized, the poppet will move.
Item #4 depicts the outer valve body, and the arrow is pointing towards the internal valve actuator, the coil spring.
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Once the direct acting solenoid valve is energized the coil creates a magnetic field and the pole piece inside the solenoid coil (#1) is magnetically pulled to the right as shown in the drawing just above.
The poppet, since it's connected directly to the pole piece, also shifts (#3), moving off one seat and onto another, and allowing the compressed air to flow through the valve.
Item #2 depicts the inner valve actuator, the coil spring, which has now been compressed by the force generated by the coil, and the movement of the pole piece and the poppet.
When this direct acting solenoid valve is de-energized, the return spring shifts the poppet and the pole piece the other way inside the valve, and the compressed air is, once again, blocked, as shown in the first drawing above.
Limited Capacity
A solenoid actuator is a pretty neat device. Maybe it makes you wonder, if all you need is a solenoid and electricity to make things move, why compressed air circuits even use air actuators at all? Why not just use solenoids to do work?
While a solenoid coil can generate sufficient force to move a small device over a short distance, the nature of the coil itself is that it would take a huge coil to move any meaningfully sized device over a distance greater than a few tenths of an inch.
In order to have a coil actuator that would do physical work, moving tooling 18" for example, the solenoid coil would dwarf the tooling and maybe the machine it was situated on. Not very practical.
More on direct acting solenoid actuators here!
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