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I've googled this, but found no satisfactory answers. I've found a diaphragm pump on amazon for $20, but it has one problem- it's designed for water. I specifically need a diaphragm pump/compressor, but they all appear to be expensive and achieve a low psi. For my application, I need a PSI of around 100, but I don't need a high flow rate. In short, Can a water pump be used to compress air? Thanks in advance.

closed as off-topic by Daniel Griscom, mmathis, Machavity, ThreePhaseEel, JPhi1618 Jan 19 '18 at 16:06

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  • if you moved the water in front of air the air will increase pressure. it depends on the flow you need, hopefully not much/any, but you might be able to rig something up. – dandavis Jan 7 '18 at 21:14
  • Because there's no such thing as a water compressor. Those words do not go together. – Harper Jan 7 '18 at 21:17
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    @Rafael - Based on your comment, this sounds like a really bad idea. Can’t you just buy a conventionally fueled torch? – Mark Jan 8 '18 at 1:58
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    ok, i'm the least cautious guy on here, but that is really dangerous. Remember boyle's law? What happens to hydrogen if the amount stays the same and volume decreases? How does a diesel engine ignite vapors w/o a spark plug? Exothermic packing aside, it's just a dangerous gases to use for fuel because it's scentless, reactive, and displacing. don't, just don't. – dandavis Jan 8 '18 at 6:06
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    I'm voting to close this question as off-topic because it is not about Home Improvement. And, I concur with the other comments: trying to save a few bucks while compressing hydrogen to 100psi seems like a great way to enrich the beneficiaries of your estate (assuming they don't live with you). – Daniel Griscom Jan 8 '18 at 12:57
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Yes, you can use a water pump to indirectly pressurize a gas with water pressure if you use a water tank with an internal air bladder. First, you drain the water from the tank. Second, you fill the air bladder with your gas through the Schrader valve. Third, you pump water into the water tank to the pressure you want your gas. Fourth, your gas in the air bladder is now the same pressure as the water in the water tank and you can remove it from the tank.

The opposite can also be done by using air pressure to create water pressure if you ever have an air compressor and need to make water flow instead.

Most tanks have a maximum rating of 100-120 psi pressure, and hydrogen fuel tanks operate at a working pressure of 5,000-10,000 psi, so I think you'll be fine using a water tank to indirectly compress hydrogen to 100 psi. Direct contact with an electric pump is the last thing you should do with hydrogen, so use this technique and you'll be safe.

Alternatively, you could replace the water pump with an air compressor like a bicycle pump and achieve similar results using this method. I would use this or a combination of both water and air in the water reservoir if your small water pump can't create the necessary pressure. Essentially you're using one bladder to pressurize a second bladder, which works because they're both trapped inside of a container with a fixed volume.

water tank air bladder

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    Thanks! This is a little complicated for me, but just one question- This doesn't seem like it can be done continually; is that correct? – Rafael Jan 10 '18 at 2:33
  • Correct, this won't work continuously. – Dotes Jan 10 '18 at 14:56

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