What is the difference between spring return and differential return air valve?

by Muntaser
(Syria)

What is the difference between spring return and differential return and where I can use each one?

I use 5/2 valve with differential return to control cylinder but this valve is suddenly stopped so when I used another valve with spring return it worked.
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Bill Answers...

Howdy Muntaser:

Whoever designed your air circuit has determined that the application is best served by using a 5/2 air valve that contains a differential air pressure return of the valve internal spool to shift the valve, and usually retract the piston rod of a double acting air cylinder.

Usually, a differential return valve will contain a spring as well.

The different force created by different surface-area sized pistons on the internal spool will use the valve supply air and the internal spring to shift the valve back when "something" has been accomplished in the air circuit.

It's hard to visualize why a differential return valve was used in the circuit without seeing the drawing or understanding the complete application.

A simple single-solenoid, 5/2 spring return is the most commonly used 5/2 valve, and the spring, when the single solenoid is de-engergized, will shift the internal valve spool back to the pre-energized state, allowing the piston rod on a double acting cylinder to retract after work has been performed.

I don't know know your circuit, but I expect that your circuit designer wanted a non-complex method to shift the valve spool back, and thus retract the air cylinder, without adding additional signal or control elements in your circuit.

When the differential valve is working, your cylinder will likely extend to do work, and after the pressure in the cylinder (and through the valve) has reached line pressure, the valve internal spool will shift back, and your cylinder will retract.

If you wish to use a simple 5/2 spring return valve, you'll need to add some control elements to the circuit to signal a valve shift when the work is performed.

Your present valve likely has a build up of contamination (see here for more info) which increases the friction between the spool and housing, and the air/spring differential can't overcome that friction to shift the valve.

Hope this helps.

Cheers,

Bill