Plumb 2 solenoids?

Do you know why we can’t plumb 2 solenoids together?

  1. R95. The outputs from multiple solenoid valves must not be plumbed together.

if you believe that both are off but one is broken/still on, you could get hurt. It’s a safety thing I think. Could also have to do with limiting the Cv teams can use per cylinder.


It’s about limiting the flow rate to actuators and other components, as 21brownz has said. This is a safety precaution, just as the limitation on both tank and working pressure is. Plumbing the outputs of more than one solenoid together could increase the flow rate to unsafe levels.

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You can’t do it because it’s a rule in the manual. We don’t get to pick and choose which rules to follow.

The reasoning behind the rule was explained by @21brownz and @Strategic


Way back when pneumatics was a dark art… The GDC limited the Cv of the solenoid valves to a small number. Intrepid teams connected multiple valves together in attempts to create powerful mechanisms. For pneumatic, Cv ratings for valves is highly dependent on test methods and varies considerably from manufacture to manufacture. After viewing numerous “Hey! watch this release videos”, the GDC added a rule prohibiting plumbing the outputs of valves together in a vain attempt to restrain the intrepid teams. Not long after this the GDC realized tubing and port restrictions were sufficient to constrain flows and dropped the Cv restrictions for the valves. However the prohibition of plumbing outputs together remains. That is my story.

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aside from the fact that you can drain your tank if one fires and the other doesn’t , I think it is in order to limit the flow to the pneumatic elements for safety

What so dangerous about connecting two valves together?

This is safety issue plain and simple. If a team designed a robot device that had a very large bore cylinder they would find that it could not move as fast as they hoped. They would try to use more than one valve in the expectation of getting much better response. In the case of a 4 in bore, the cylinder is capable of exerting in excess of 750 lbs of force. By limiting to one valve, this should allow a team member to remove their hand before the cylinder makes full travel. The reality is the size of the fittings on the cylinder and the size of the tubing will still reduce the flow, however, it may not be a sufficient reduction to keep teams safe.
And yes, I have had a team show up with a 6" bore cylinder in the past.

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Yeah, I guess I figured most people would understand that we were curious about the reasoning behind why it was a rule… thanks though!

Alright, now I’m curious: what the heck were they using a 6" bore cylinder for?

They had it so they wanted to use it. A mentor brought it in. It was cool but they had no real application for it when they showed me the device. They just noticed that it moved really slow.

My safety guy says that the correct answer is don’t stick you hands in a pressurized pneumatic mechanism in the first place. Automated machinery (IE robots) are inherently dangerous. Which is why lock out tag out (LOTO) laws exist. Just having one valve is marginally safer than two valves on a well designed mechanism. A case could be made that the work around for flow restrictions are more dangerous than not having the restriction is the first place.

I am not really arguing against the rule.Rules are rules. We work with what we have.

The key words there are “well designed”. While there are quite a few teams that do amazing advanced and safe designs, many teams simply don’t have sufficient experience to ensure industrial levels of safety when there are other competing design constraints/goals to follow on a short timeline. Many of FRC’s robot rules are designed to protect teams from themselves (another example of this is the restrictive motor controller rules).

And it’s always worth keeping in mind that “what we have” are high school students, who are unskilled, untrained, and unpracticed compared to those who work in industry–and also have those impulsive, not-yet-fully-developed teenager brains that yeet when they should not yeet.

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Sort of my point. Not allowing the second valve really isn’t protecting teams from themselves. You can be almost dangerous as with one valve. :slight_smile: To be fair: The GDC didn’t consult me in making this rule. They may well have had another reasons for having it.

While not really relevant to the current discussion, I actually take safety seriously. Which is one reason I dislike safety theater. Safe work practices should be top of the list of what we are teaching. It starts with using your brain.