I want to use an external gear pump to pump air into a combustor at a design pressure of 3 atm.

Unless i use a valve that opens at threshold pressure there is no compression - the air exists the pump at close to atmospheric pressure.

Normally in this situation one would use a spring loaded valve.

But since the combustion at the combustor is isobaric, a spring loaded valve won't open when the engine is running cause there would be no pressure difference between the sides of the valve so no net force to compress the spring.

Is there a valve that will only open when input pressure is above 3 atm when the downstream pressure is atmospheric but also when the downstream pressure is also 3 atm?

  • $\begingroup$ Find a way to change the pressure. $\endgroup$
    – Solar Mike
    Oct 30, 2021 at 19:01
  • $\begingroup$ i don't understand $\endgroup$
    – Francis L.
    Oct 30, 2021 at 19:44
  • $\begingroup$ you could set something up with a pilot actuated valve (e.g. with the pilot pressure raised by the pressure relief valve and relieved by a flow restriction like an orifice). There is probably already an existing valve designed for this application $\endgroup$
    – Pete W
    Oct 30, 2021 at 21:25
  • 1
    $\begingroup$ you are talking about a pressure control valve. It isn't any more complicated than that. $\endgroup$
    – Tiger Guy
    Oct 31, 2021 at 0:15
  • $\begingroup$ I think you might need to buy a gas pressure regulator. As long as you don't need a large flow rate, it shouldn't cost you too much money. The regulator has a chamber which senses both the upstream and downstream pressure and opens the valve depending on the pressure set by the engineer and the pressure delta. Then just put a check valve and service valves after the regulator. You could also use a bang-bang pressure control system if you only need a quasi-isobaric situation, and precision is not core to this device. $\endgroup$ Oct 31, 2021 at 23:41

1 Answer 1


Thete are 12-24 automatic valves at Amazon, reasonably priced.

You could set them for the pressure or temperature, or programable. the price range is $60-100.


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