Solenoid Actuator

A solenoid actuator, or solenoid actuators, are one of a host of different ways to operate compressed air valves including manual levers, push buttons, palm buttons, roller cams, whisker switches, to name just a few.

When I write about the various methods to actuate an air valve I use the term actuator for the electrical or 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.

Here is some background information on air valves if you are interested.

Two Solenoid Actuators

There are two kinds of solenoid actuators for air valves. One is covered here on this page, that being the Direct Acting Solenoid actuator and the other is covered the Air Pilot Solenoid actuator, right here.

Solenoid Definition

Here is a quick definition of a solenoid: "as it relates to compressed air valves, a solenoid is a device that, when energized with electricity, creates a magnetic field that generates motion."

Depending on the type of air valve, the item this the solenoid magnetic field moves could be a device to control air flow through a small or a larger air valve.

Direct Acting Solenoid Actuator

2/2 Air Valve Schematic

In the drawing above, item #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 this valve which is a 2/2 normally closed valve, the 2/2 meaning two ports and two postions.

Please 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 stream from flowing through the valve and out the other port.

The coil on this valve is de-energized, and the internal valve actuator, which is a spring, is in control at this time, shutting off the air flow.

The solenoid coil, when it is energized, creates a magnetic field which will move the pole piece (item #3 - brown color) inside the coil housing. In this example, the pole piece will move to the right. Since it is attached to the poppet inside the valve, when the coil is energized and the pole piece is moved by the magnetic field, the poppet will move along with the pole piece.

Item #4 depicts the outer valve body, and the arrow is pointing towards the internal valve actuator, the coil spring.

2/2 Air Valve Schematic

When the direct acting solenoid valve is energized the coil creates a magnetic field pulling the pole piece to the right as shown in the drawing just above.

The poppet, connected directly to the pole piece, also shifts (#3), moving off one seat and onto another, and now 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.

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 circuit designers even design in air actuators at all? Why not just use solenoids to do work?

While a solenoid coil can generate sufficient force to move a small, very light device over a short distance, the movement length and the size of the item being moved is limited. It would take a huge electric coil to move any meaningfully sized device over a distance greater than about one-tenth of an inch. In order to have a coil actuator that would do meaningful physical work, moving some heavy tooling 18" for example, as an air cylinder using the power of compressed air can easily do, a solenoid coil needed to generate that force and distance would completely dwarf the tooling and maybe even the machine it was situated on. Not very practical, and very, very expensive.

Here is more information about direct acting solenoids.