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I have two containers of air, one at 100 kPa and rising, the other at 30 kPa and decreasing. I need a valve that lets air through when the pressure difference is >70 kPa. Where would I find a valve like that? If nowhere, do you have any pointers on how to make one?

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Check Valves are available with adjustable cracking pressures, using a preload spring to control the poppet force, for example: http://www.my-ssp-usa.com/products/valves/check-valves/adjustable-cpa

It's important to note, however, that there is a degree of histeresis with these valves, and once open, they will not close if the pressure difference drops a bit - it will have to drop lower than your application may allow. A Back Pressure Regulator may be more suitable.

Adjustable Check Valve:

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  • $\begingroup$ Thanks, that's what I was looking for. Although the industrial ones are insanely expensive. I found these: solenoid-valve.world/other-products/FRL/… bes.co.uk/… Is any of these two what I'm looking for? $\endgroup$ – Peter Poláček Oct 22 '18 at 14:31
  • $\begingroup$ No - a pressure regulator sets a downstream pressure when given a high upstream pressure, but a back pressure regulator sets an upstream pressure when given a low downstream pressure. $\endgroup$ – Jonathan R Swift Oct 22 '18 at 14:53
  • $\begingroup$ But isn't a pressure regulator essentially a check valve? If it relieves pressure on the other side after reaching a critical value, that would work for me (I now realize I misspoke, I don't care about the lower pressure, I just need the pressurized chamber to stay close to 100 kPa). Although it would still depend on the pressure on the other side? $\endgroup$ – Peter Poláček Oct 22 '18 at 15:32
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    $\begingroup$ A pressure regulator doesn't care what the upstream pressure is. If the downstream is lower than the setpoint, it will open to let more gas in. If it's higher, it will close. This doesn't sound like what you want? $\endgroup$ – Jonathan R Swift Oct 22 '18 at 15:58
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    $\begingroup$ I also thought I'll get a pressure sensor in the high pressure chamber, ass a valve and open it periodically to let air out. It will all be controlled by an arduino so might still work. Thanks for your help! $\endgroup$ – Peter Poláček Oct 22 '18 at 19:29

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