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Valve that vents when the pressure of another inlet is high

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Valve that vents when the pressure of another inlet is high

Unread postAuthor: btrettel » Tue Sep 08, 2009 10:39 am

I'm looking for a valve that will vent (or redirect as that can be used to vent) one inlet when another inlet's pressure reaches a certain (ideally user defined) level. Does anyone know anything like this? I'm looking for something in 10-32, 1/8" NPT, or 1/4" NPT (preferably 1/8" NPT).

The closest thing I've found are some air piloted valves (by Clippard) that when used in combination with an orifice (for timing) can do basically the same thing. I'd have to do some simulation to figure out what diameter orifice would get the desired effect, but that shouldn't be too difficult. I'd still prefer buying one item that acts when the pressure reaches a certain level.

I also could redesign what I want to do such that the chamber I want to vent is always leaking (when a different valve is activated, at least) and is simply refilled, but this would likely be too slow to be practical.

Building a valve like this shouldn't be too difficult... however I don't have the patience or time to make one at the moment.

If anyone's interested, this is for a novel water gun idea I've had.
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Unread postAuthor: cannon monkey » Tue Sep 08, 2009 12:51 pm

do you mean like one of these?

http://www.spudtech.com/detail.asp?id=45

sorry but it the only picture i could find it vents the air out of ( any thing it screwed into can buy at differnt pressure ratings this one will open at 125 psi

you can buy them at any store ace lowes homedepot
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Unread postAuthor: btrettel » Tue Sep 08, 2009 1:01 pm

No. A pop-off valve vents from the same place that detects the pressure. I want venting from a different chamber completely from the one where the pressure reaches a certain level.
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Unread postAuthor: cannon monkey » Tue Sep 08, 2009 1:03 pm

ok so u want say
chamber A
and
chamber B???

when chamber A gets to ( let just say 100 psi) u want chamber B to vent?
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Unread postAuthor: btrettel » Tue Sep 08, 2009 1:04 pm

Precisely. I'd also prefer the pressure level to be adjustable on the fly as I do not know what level is appropriate yet.
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Unread postAuthor: cannon monkey » Tue Sep 08, 2009 1:05 pm

mm well do u want all of chamber b to be empty?
or is it like

ur fillin A once you hit X ( unsure what pressure so X ) x psi u want chamber B to shot out all of the water?
using pressure from A?
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Unread postAuthor: btrettel » Tue Sep 08, 2009 1:07 pm

Both chambers will contain gas. Water is in a different part.

I want the valve to stay open as long as chamber A's pressure is above X. Chamber B does not necessarily need to vent completely but should be mostly vented.
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Unread postAuthor: cannon monkey » Tue Sep 08, 2009 1:09 pm

would a normal sprinkler valve work? and have it opened by a pressure switch?

the valve on chamber b and the switch on chamber A

at X pressure the switch is turned on opening the valve?
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Unread postAuthor: btrettel » Tue Sep 08, 2009 1:13 pm

Probably. But I'd prefer to avoid electronics completely and that seems more complicated than the air pilot valve and orifice combination I mentioned.

Similarly, you could probably do something like what I want with a QEV and the right logic, but it'd be more complicated than the already complicated solution I thought of.

To be more explicit, I'm wondering if there's a single off-the-shelf valve (or at least simpler or cheaper combination of components than what's already been considered) like what I want.
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Unread postAuthor: cannon monkey » Tue Sep 08, 2009 1:16 pm

that i do not know i was thinking like them 50 gallon air compressors once they hit X psi in the tank they turn off
so idk i tried tho :D sorry i couldnt give you the valve you needed i keep thinking how to do that using air
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Unread postAuthor: POLAND_SPUD » Tue Sep 08, 2009 1:16 pm

it would be really easier if you say what you need it for...

from your description it seems that you are looking for a regulator...
:wink:

is it really all about pressure or do you want to build a pneumatic timing circuit with it?

EDIT
you could use a pneumatically actuated valve with spring return

open it up and replace the spring with a stronger one... it should switch at a higher pressure


there are pressure dependant valves...

http://www.coastpneumatics.com/festo/Pr ... Valves.pdf

I even think that clippard has them but I don't have the patience to download their PDF and it crashes mozilla when I open it...
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Last edited by POLAND_SPUD on Tue Sep 08, 2009 1:51 pm, edited 1 time in total.
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Unread postAuthor: Technician1002 » Tue Sep 08, 2009 1:43 pm

A simple double acting pneumatic cylinder connected to a valve will do the trick. Or even a pneumatically operated valve without a spring return and double acting cylinder will work.

The two cylinders are connected to the "actuating" cylinder. When on port is higher than the other, the valve operates on direction. When the pressures are reversed the valve moves the other direction. You pick open or closed.

Hook one of these double acting actuators to your valve.
http://www.abzvalve.com/PDF/227%20DA%20Torque.pdf
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Unread postAuthor: btrettel » Tue Sep 08, 2009 2:01 pm

I need a valve as described is all that's necessary to understand. I'll make a diagram later today of the setup, but the explanation of how the water gun works will likely complicate matters further. This basic cycle isn't too complicated; the problems come from attempts to make it more gas efficient.

I'm not looking for a regulator. Pneumatic cylinders actuating a valve would do the trick, but it is more complicated and bulky than an air-pilot valve and an orifice for timing. (Note that the similar approach of a valve with a small pneumatic cylinder opposed by a spring with the position of one end set by a screw with the cylinder pushing on a spool valve is how I'd make one of these valves if I were going that route. Sorry if that's hard to understand.)

It's less about pressure and more about the position of a piston. But, the piston will stop due to a pressure differential; so by extension it's also about pressure. Making a switch that notes the position of a piston is far more complicated than measuring the pressure of a chamber.

I suppose the valve I want doesn't exist (yet). I'll get an explanation up later today anyway. Maybe someone can make the design avoid this problem completely.
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Unread postAuthor: Ragnarok » Tue Sep 08, 2009 2:05 pm

Yes, such valves can be bought. To the best of my knowledge, they're normally called air actuated valves, and you'll probably want a double acting one so you can feed a fixed pressure to the closed side to act as an air spring.

Try looking at this page and see if that matches what you want:
http://assuredautomation.com/VA/index.php

Prices are not normally very pleasant though.
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Unread postAuthor: btrettel » Tue Sep 08, 2009 2:17 pm

Thanks Ragnarok. That does exactly what I need.

Shame that the prices and sizes are wrong, but it definitely sets my research in the right direction.
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