Solenoid Actuators;

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Direct Solenoid Actuators

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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 even maybe the machine it was situated on. Not very practical at all.

That's why we use compressed air to provide the mechanical force (through the air actuator) to do the "heavy lifting".

Compressed air valves that are being actuated by a direct acting solenoid must be fairly small.

A small valve body means that the poppet or spool that controls the air flow inside that body is smaller yet. It's light weight, and it only has to move a short distance.

Those are ideal operating conditions for a direct acting solenoid actuator.

Don't Push The Limits!

Direct acting solenoid valves are relatively inexpensive to manufacture. Which is why air valve engineers are always trying to maximize flow through the direct acting valve, by trying to increase the valve's flow capacity, without enlarging the body too much, and keeping the solenoid coil as small as possible.

Unfortunately, when air valve designers push the limits of air valve size using a direct solenoid actuator, valves tend to stick more often.

The water and crud that comes down the air line deposits contamination inside the valve body.

If that air valve sits idle for some hours between operations, that guck inside the valve dries out and sticks the parts together. When the valve is ordered to fire again, there's not enough force in the coil to overcome the stickiness inside the valve body and bingo!, you have a stuck valve.

Anybody have a hammer??? :-)

Benefits

Direct acting solenoid valves can be very, very small, with extremely low electrical demands. This is ideal for circuits that want to have their solenoid valves powered right from a PLC (Programmable Logic Controller).

Given that the solenoid actuator is only moving a very small device inside the valve a very short distance, direct acting solenoid valves can operate very quickly.

I recall I was giving a demonstration to a bunch of maintenance engineers on the relative merits of a particular brand of valve at one time. I used an oscilloscope that could generate a wave on the screen to visibly demonstrate that the little direct acting valve was cycling at over 200 times per second.

That's over 200 hertz! Opening, allowing air to flow, and closing, shutting off the compressed air, at more than 200 times every second. Amazing!

Problems

As noted earlier, since direct acting solenoid valves have, by nature of their design, to be quite small, that means that their direct operating solenoids are small too.

If the compressed air supply is marginal, full of water, water vapor, compressor oils, rust and scale from black pipe...and there isn't a decent compressed air filter to strip the crud from the compressed air supply, then small direct acting solenoid valves may stick more often than their larger, more powerful, cousins.

If the application calls out for a physically large valve with higher compressed air flow, and we've already discussed what happens when you try to actuate a valve with a poppet or spool that's too large for the force of the solenoid...it sticks, what happens when you need to solenoid operate a bigger valve?

You need to move to a solenoid air pilot actuated compressed air valve.

Get information on Solenoid Pilot Operated Air Valves here.







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