I purchased an old over-head pin router for my woodshop. It uses two solenoid valves. They are apart of the assembly that lowers and raises the rotating spindle. When the electric foot pedal is pushed, I would have assumed that the first solenoid would be activated, (allowing the air to lower the spindle), while at the same time the second solenoid would be turned off. (Right? Wrong?) Then when the foot pedal is pushed again the 2nd solenoid would be activated and the first turned off, allowing the air to raise the spindle.

But what actually happens when the pedal is pushed, is that both solenoids are turned on at the same time (securely lowering the spindle), and when the pedal is clicked again, both solenoids are turned off and the spindle remains where it is (although it can be raised by hand). Are my assumptions wrong? There are no return springs. Is it possible both solenoids are used to force the spindle down (holding it securely during the routing), and then when the solenoids are turned off the air pressure alone is supposed to return the spindle to its up position? (Implying there is a non-electrical impediment?) Thanks ahead of time for brainstorming with me.

  • \$\begingroup\$ Woodworking SE might be a better bet... \$\endgroup\$
    – user16324
    Aug 27, 2017 at 21:53
  • \$\begingroup\$ What kind of valves you have, and possibly the pneumatic schematics. This question is also for a different forum. \$\endgroup\$ Aug 27, 2017 at 22:26
  • \$\begingroup\$ Oops - rookie mistake. They are Peter/Paul Elect. Co solenoid valves (Long outdated #026X00010CV). They sit side by side, and each coil fits over a vertical tubular post, and the sliding pin is inside it. When activated the pin rises and the rubber seal that covers a hole in the bottom is lifted allowing air to rush in, through the tubular post and out the top where a copper tube takes it to the cast iron housing that contains the spindle. As to a schematic - I can only dream. But one does not exist. \$\endgroup\$
    – CNB
    Aug 27, 2017 at 23:14

1 Answer 1


Solenoid valves come in many variations, sort of analogous to normally open and normally closed contacts, but they also need to provide a path for the air (or hydraulic fluid) to escape the cylinder.

In your case you have a double-acting cylinder since there are no springs. Here is one way to operate a double-acting cylinder using two 3-way valves from this reference:

enter image description here

You force air into one port to extend the cylinder, allowing air to exhaust from the other part. Retracting the cylinder is just the opposite. There is a more force available when extending the cylinder since the whole bore area multiplied by pressure is available when extending, whereas the area of the rod must be subtracted from the bore when calculating the retraction force.

Both valves would be powered at the same time to extend or retract the cylinder (depending on the valve type and how the valve ports are connected to the cylinder ports).

It sounds like one of your valves is not operating correctly.

  • \$\begingroup\$ It did not occur to me that the solenoids were different from each other - I assumed they were identical. If I understand you correctly, both would be activated, but the first solenoid would be set to open, and the other close. And when the coils released, they would do the opposite (the first solenoid would close, and the other open. I will have to take them both apart and check this out. But it would explain why both are activated and released at the same time. Something to focus on. Thanks. \$\endgroup\$
    – CNB
    Aug 27, 2017 at 23:23
  • 1
    \$\begingroup\$ They could also be the same and piped differently. Check the part numbers. \$\endgroup\$ Aug 28, 2017 at 1:25
  • \$\begingroup\$ That was a great suggestion, and I expected to find they were different part numbers. But... they were not. They were identical. So I am a little confused. \$\endgroup\$
    – CNB
    Aug 29, 2017 at 1:35

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