Double Acting valves / cylinders

Hi,
Please excuse a very basic newbie question.
I want to use a PLC to move a double action pneumatic cylinder.
Apply 24V to one end , moves left. Remove 24V and apply to other end,
moves right. Fine so far.
My question is should the 24V stay on for as long as the cylinder is held in one direction or will the cylinder stay in the last position it was set to with power removed?
This is obvious to me with a single action cylinder with spring return, but not with a double.
Thanks,
Dave.

It depends a litlle bit on the make of the valve.

I've seen hazards due to the fact, that the 24VDC was not supplied at all times, when needed to be at one end. Especially at working machinery. The valve simply moved due to vibrations.

So my advise is to apply the voltage for the duration of time, you need the valve to be at either end.

Yes, it depends on the valve. A 2-position valve will remain in its last state. A 3-position valve returns to center when neither solenoid is energized.

I'll make a guess that you probably have a 2-position valve. There is usually no harm done if you keep the solenoid energized.

beerchug

-Eric

Thanks very much for your help.
Dave.

A 3-position valve returns to center when neither solenoid is energized.

Click to expand...

Not always.

Some have a 'detented spool' - they stay in position with power removed.

The choice of which to use depends on what needs to happen, or not happen, on loss of power.

Gerry-
I have never come across a 3-position valve with a detented spool. I'm not even sure how that would operate with only two solenoids. What manufacturer's valve have you seen this on?

Keith

oops

my apologies, Eric

brain wasn't in gear before engaging mouth

I was thinking of valves with two solenoids, not 2-pos / 3-pos.

Dave,

It's like ejessen and Eric says - it depends on the valve.

But: it does not depend entirely on whether it is a 2- or 3-position valve. It depends if the valve has spring return or not.
A 2-posistion valve can have 2 solenoids and be bi-stable, i.e. it remains in the last activated position. Or it can have spring return and one solenoid.

As Keit, I have never seen a 3-position valve which do not return to centre position.

You can leave one of the solenoids activated on a bi-stable valve at all times without any damage, but never both at the same time!

Anders