Looking for a rule and sanity check here. I THINK this should work, but could use some extra eyes on it. I was thinking of having a mechanism that can be actuated with different pressures. As such, what i would seem to need is a solenoid with 2 inputs and 1 output. I would need this without the 2 inputs being connected to each other, else the pressures would equalize and render the whole thing useless, and without either bleeding to atmosphere.
So this is what i came up with. 2 solenoids in series, with the first one flipped and capped (2 inputs connected to the output terminals, single input becomes the output, and 2 remaining terminals are capped to prevent either bleeding out) toggling between high and low, and a second solenoid plumbed normally actuating the cylinder bidirectionally.
I know pneumatics roles lately have been quite lax, so I dont expect to find anything explicitly forbidding it. Closest I found is R814, but that seems to be referrong to valves in parallel (multiple outputs controlling a single actuator).
Is there a practical/functional reason the first valve wouldn’t work reversed like this? I’m intentionally not mentioning model numbers because frankly I have no idea which one(s) I’d use for this. But I recognize that there may be different answers depending on the type of valve.
R813-A. If you somehow have stored air between the two solenoids, you’re in violation.
That, and I’m pretty sure you’ll have some issues with the solenoid itself.
Let’s step back one step further. You have a mechanism that you say you want to actuate at different pressures, yes? OK, now: Why? What is the goal you ACTUALLY want to get to, because there may be a way to do it without using two different input pressures to one solenoid.
(For the record, if you’re doing what I think you’re doing, I might try using two different solenoids and two different motion methods, with each set to a different pressure via regulator.)
For R813-a, is pressure actually stored between them? The first solenoid only has 2 states, open to low-pressure source, or open to high-pressure source (“high” being <= 60psi of course). As such, if I bleed from the stored-pressure (120psi) side, it would bleed the 2 lower pressure branches, which would allow pressure to release between the two valves as well. And the second solenoid will have one side open to the “middle” segment, and the other open to atmosphere, so I’m not seeing anything being trapped.
But yes, I’m almost certainly looking at doing what you’re thinking I’m doing, so I’ll spare the details. In short, the thought was for game-piece pickup, if a higher pressure were needed for grasping the cone whereas a lower pressure were needed for grasping the cube (without risking popping it). This is purely theoretical at this point, I don’t even have a mechanism in mind yet and therefore have done precisely zero testing.
If I were doing that, I’d be thinking 2-jaw design with one jaw using each pressure.
That said, I think there might be a technical problem.
You have your solenoid, and normally you feed it through the input, air goes through output one, and output 2 is vented to atmosphere. (Depending on solenoid type, to be sure.) That might could be a bit of a problem.
Would it also be possible to design it with 2 pistons the same way 118 did for their intake actuation on their 2022 robot (but this time using idential cylinders) and just having one high pressure one low pressure, using a different one depending on which game piece you’re collecting? that way it could use the same jaw. it’s pretty late here, that may be physically impossible but that’s my take.
Yeah, this was the purpose of the first valve being flipped. The input becomes the output, and the 2 output branches become the 2 inputs. The remaining to ports (normally open to atmosphere) will be capped to create a closed circuit. This should work in my mind as the whole system up to this point is functionally equivalent to a single input. The bleed to atmosphere necessary for the cylinder to actuate would occur at the 2nd valve
Possible? almost 100%. I’m just trying to minimize moving parts I guess. If I can reuse the same mechanical components, same cylinder, etc, then it’s a “simpler” design in my mind. I can make pneumatics play nicely, but I’m very much not a precision machinist (or is anyone else on my team, though we get by with what we have).
That could run you afoul of the stored pressure release–depends on how the solenoid switches, and if anything remains in the capped side when the switch happens.
I think I might run this by your local LRI, if I were you.
I’ve actually already texted him, but I think he’s asleep at this point.
That said, I still don’t see where it would. It’s not functioning the same way a household 3-way switch circuit would, where there’s a leg that’s “dead” in between the two (aka retaining pressure), and the 2nd valve functions identical to the normal setup (and therefore can’t be the cause of retaining pressure on its own).
In either case, I could absolutely see this being a conversation with an inspector where we have to essentially prove that it’s fine.
My primary concern was that there’s a functional limitation in these valves (e.g. that they REQUIRE pressure to be applied to the standard inlet port in order to actuate) that would prevent this from working due to the flipped valve. If there’s no rule this would violate, then I could certainly do a quick benchtop test of this.
Yeah, this was what I came up with after a solid 45 minutes of staring at it. With solenoids oriented the “normal” way, there always seems to be something bleeding to atmosphere.
I didn’t get too crazy with it though, like having the output of one feeding into the exhaust port of the other or whatever… mostly because that kinda makes my head hurt…
Plumb the higher pressure to the valve then the outlet to the shuttle valve. Plumb low pressure to shuttle valve. Plumb outlet of shuttle valve to other solenoid. Now you can turn the high pressure on/off, and the shuttle valve directs the higher pressure to the control solenoid.
edit: We used this general setup to save some additional air for climbing in seperate tanks we could trigger at the endgame. Also, something I saw above was about using a solenoid on the high pressure side, which is not allowed.
Sorry, mincing terms. For the sake of clarity, “high pressure side” refers to the higher of the two working pressure segments. This entire system would be downstream of the 60psi (max) regulator to be compliant with the rules. “high” pressure in this case would refer to, say, 60psi, whereas “low” might refer to 30psi.
The shuttle valve is a nice touch. This is where I lack experience (I’m primarily a software guy), so I didn’t even know that was a thing.
So if I understand correctly, the two-position solenoid is functionally an on/off switch for the “high” pressure circuit. In the “off” state, the shuttle valve will allow things to equalize at the “low” pressure. Then the second solenoid functions exactly as normal (same as mine) in controlling the cylinder. Correct?
Yeah, that pretty much is it. Yeah by high pressure, mean before any regulator. 120 psi approx. I think Eric might have said something about the solenoid there, so was clarifying that before regulators you can put just a few restricted parts (i.e. relief valve, pressure switch, exhaust valve).
Just to add to any potential confusion, I’m also “Eric”… I should probably update my display name on here, but so many people already know me as Fletch…
