Diaphragm Pumps for Gas

[MadMan]

I've been messing around with a diaphragm I've gutted from an old keurig machine.

I'm trying to learn more about gas compression methods, and the transportation of gasses.

I believe the pump was intended more for water than air (gasses), which might be much of why I am having a hard time achieving higher psi through this pump.  In what I've gathered so far: the weak point seems to be the actual diaphragm itself.  The check valves should operate the same no matter what pressure is applied because of the counteracting forces.  I believe I foolishly tried to increase the area of expansion and contraction of the diaphragm by replacing it with a balloon.  It appears the flexibility of the latex inhibits the suction and repulsion needed to actuate the compression.

Whether with the balloon, and some manual fiddling, or with the original diaphragm: I can only seem to get up to ~10 psi; if the pump is wet/damp, and ~8 psi; if the pump is dry.

I've had trouble finding help online.  I've mostly ran into people selling their pumps.  I'd like to more deeply understand what is going on here, and if I'm missing anything.

Any suggestions on what I could do to either improve my current process, or what fundamentals I'm missing to study up on to further my understanding would be greatly appreciated.

Thanks in advance.

[exchemist]

9 hours ago, MadMan said:

I've been messing around with a diaphragm I've gutted from an old keurig machine.

I'm trying to learn more about gas compression methods, and the transportation of gasses.

I believe the pump was intended more for water than air (gasses), which might be much of why I am having a hard time achieving higher psi through this pump.  In what I've gathered so far: the weak point seems to be the actual diaphragm itself.  The check valves should operate the same no matter what pressure is applied because of the counteracting forces.  I believe I foolishly tried to increase the area of expansion and contraction of the diaphragm by replacing it with a balloon.  It appears the flexibility of the latex inhibits the suction and repulsion needed to actuate the compression.

Whether with the balloon, and some manual fiddling, or with the original diaphragm: I can only seem to get up to ~10 psi; if the pump is wet/damp, and ~8 psi; if the pump is dry.

I've had trouble finding help online.  I've mostly ran into people selling their pumps.  I'd like to more deeply understand what is going on here, and if I'm missing anything.

Any suggestions on what I could do to either improve my current process, or what fundamentals I'm missing to study up on to further my understanding would be greatly appreciated.

Thanks in advance.

Im not an expert on this but I wonder if the valves may not work so well with a compressible medium as they do with an incompressible one. If the %volume change of the pump chamber over its operating cycle is not that great, the pressure differences it creates may be too small to actuate the valves properly. This could explain why, when the pump is wet, you get  better pumping, due to the moisture helping to seal round the edges of the valves, or else that it lubricates them so they function more smoothly. Whereas, when the pump is operating with a liquid medium, the pressure from whatever actuates the diaphragm will be instantly transmitted in full to the valves, because the fluid is incompressible, making the valve action more positive.

But this is only speculation on my part, based on dimly remembered experience of dismantling an SU electric fuel pump on a Morris Minor I owned in the mid 1970s, when I was a student.  

Edited November 26, 2022 by exchemist

[sethoflagos]

14 hours ago, MadMan said:

I've been messing around with a diaphragm I've gutted from an old keurig machine.

I'm trying to learn more about gas compression methods, and the transportation of gasses.

I believe the pump was intended more for water than air (gasses), which might be much of why I am having a hard time achieving higher psi through this pump.  In what I've gathered so far: the weak point seems to be the actual diaphragm itself.  The check valves should operate the same no matter what pressure is applied because of the counteracting forces.  I believe I foolishly tried to increase the area of expansion and contraction of the diaphragm by replacing it with a balloon.  It appears the flexibility of the latex inhibits the suction and repulsion needed to actuate the compression.

Whether with the balloon, and some manual fiddling, or with the original diaphragm: I can only seem to get up to ~10 psi; if the pump is wet/damp, and ~8 psi; if the pump is dry.

I've had trouble finding help online.  I've mostly ran into people selling their pumps.  I'd like to more deeply understand what is going on here, and if I'm missing anything.

Any suggestions on what I could do to either improve my current process, or what fundamentals I'm missing to study up on to further my understanding would be greatly appreciated.

Thanks in advance.

When you refer to 'an old keurig machine' are we talking about a coffee machine?

In which case it will probably be the air purge pump. Google tells me that these typically have a maximum rated air output pressure of 350 mmHg. 

[MadMan]

6 hours ago, exchemist said:

Im not an expert on this but I wonder if the valves may not work so well with a compressible medium as they do with an incompressible one. If the %volume change of the pump chamber over its operating cycle is not that great, the pressure differences it creates may be too small to actuate the valves properly. This could explain why, when the pump is wet, you get  better pumping, due to the moisture helping to seal round the edges of the valves, or else that it lubricates them so they function more smoothly. Whereas, when the pump is operating with a liquid medium, the pressure from whatever actuates the diaphragm will be instantly transmitted in full to the valves, because the fluid is incompressible, making the valve action more positive.

But this is only speculation on my part, based on dimly remembered experience of dismantling an SU electric fuel pump on a Morris Minor I owned in the mid 1970s, when I was a student.  

To see if I'm understanding what you're saying, let me try to rephrase it.

If the pump is made for liquids (a much less compressible medium), then the seals for the check valves may have a reverse breakdown at a lower pressure with gas (a much more compressible medium).  This being due to the seals not being as strong.

That makes sense to me.  I figured that the way check valves function this wouldn't be the source.  However, less effective seals around the valve would explain it somewhat.

 

41 minutes ago, sethoflagos said:

When you refer to 'an old keurig machine' are we talking about a coffee machine?

In which case it will probably be the air purge pump. Google tells me that these typically have a maximum rated air output pressure of 350 mmHg. 

Yes, that is what I'm talking about.

So the actual use of this pump in the machine is a vacuum, which involves different forces than compression (if I'm understanding correctly).  According to my tests, that spec seems to match.  However, I did also save a separate check valve that was somehow connected to this pump, as well as a smaller pump (the actual name of it escapes me currently).  It doesn't seem to create enough negative or positive pressure to overcome this valve, but I may be overlooking how it was implemented.  I vaguely remember how it was attached to the machine.  Different tubes stemmed off a 4 output plastic tee, one of which has the check valve on it.

Although it may have not been your intent: I thank you for giving me somewhere to look.  Although it probably should have been obvious: if I can find some schematic of how this pump was incorporated into the machine, I could deepen my understanding of it.

Still doesn't define how I could increase the power of it, but it's something to go to.

Edited November 26, 2022 by MadMan

[OldChemE]

You may not have fully understood one of the subtle points of Exchemist.  He mentions compressible and incompressible fluids.  With water, when the diaphragm moves it creates an instant large pressure change because the water cannot compress or expand.  This is what gives good flow.  With a gas, when the diaphragm moves the gas simply expands or contacts to fill the space, and you get a significantly smaller pressure change.  This is the fundamental problem with trying to use a diaphragm pump to move gasses.  It doesn't man it won't work, but the efficiency will be poor compared to pumping water.

[npts2020]

If you can get a (relatively) low pressure water pump to get anywhere near 10 PSI with air, you are doing quite well, IMO. In general, water pumps don't make very good air pumps but air pumps *may* make fine water pumps (if you don't mind a bit of leakage and can keep from burning the pump out). In a closed system, air pumps are made primarily for compression of fluid (air) whereas water pumps are primarily for transport of fluid (water). Pumps made to do both air and water compromise a bit either way and are not as efficient as one or the other but are apparently efficient enough for certain uses.