SpudFiles

Well, I've cast a piston, turned an o ring retainer (it's floating o ring et cetera), cut my aluminum stock to size and found a hardened steel rod for the pump shaft. Tomorrow I'll head to Nev's and buy an elbow for the bottom of the pump. Adapter may be schrader or quick connect, dunno. QD is easier but schrader is more convenient for me.

Basically the check valve has me stumped. I was originally going to use a small ball based check valve with a plastic body ripped from a ball pump Next option is a schrader valve, the ones I buy for 60c each here crack at 40-50 psi. Which isn't brilliant, but not awful. However, I can buy the long valve stems with the exterior spring and mod them for 0 psi cracking pressure. Is there a problem with this? Will it work? Will it fail to seal when I start pumping at low pressure? (backflow)

Any opinions on those upper two options- standard pressure will be around 300 good ol' psi, up to even 400 psi.

Thanks doodz.

should have just pm'd gippetto on this one
i'm no expert but i would think if pressure was pushing on one side of the schrader and it was higher than the other side it should seal it and act as the spring does in returning after each pump.I think it might have some problems at lower pressures maybe to could use part of the springs they have in pens to create a lower cracking pressure idk if it will work but its worth a shot

It takes a certain amount of pressure to seat them. I suppose that if I fit it up with a QD (fem) on the pump, and male with a check valve on the gun..

I could then use the compressor to pump the first 110 psi, which will be a godsend to my arms as it's no low volume gun.

Failing that, I'll buy a check valve or make one.

Totally unrelated to your question, but important in the check valve, is the amount of total dead space. I mentioned this due to the pressure mentioned.

For example if your dead space (including in the check valve and pipe to it) is 20% of the pump volume, then at 20 bar, there will be no air delivered. Air will simply compress to 1/20th the space and then re-expand. Plan your checkvalve, piston, seals, etc to have as little as possible dead space so the compressed air is pushed out the check valve, not left in a space to re-expand.

400 PSI is 27.5 bar. Compressing to only 20 bar won't get any out the check valve. It won't pump to 27 bar in the example given.

The above does not account for compression heating which does help get more through the valve.

Technician1002 wrote:Totally unrelated to your question, but important in the check valve, is the amount of total dead space. I mentioned this due to the pressure mentioned.

For example if your dead space (including in the check valve and pipe to it) is 20% of the pump volume, then at 20 bar, there will be no air delivered. Air will simply compress to 1/20th the space and then re-expand. Plan your checkvalve, piston, seals, etc to have as little as possible dead space so the compressed air is pushed out the check valve, not left in a space to re-expand.

400 PSI is 27.5 bar. Compressing to only 20 bar won't get any out the check valve. It won't pump to 27 bar in the example given.

The above does not account for compression heating which does help get more through the valve.

actually, 20% is 1/5, not 1/20, so your max would be 5 bar. but the idea of deadspace is important.

ramses wrote:

Technician1002 wrote:Totally unrelated to your question, but important in the check valve, is the amount of total dead space. I mentioned this due to the pressure mentioned.

For example if your dead space (including in the check valve and pipe to it) is 20% of the pump volume, then at 20 bar, there will be no air delivered. Air will simply compress to 1/20th the space and then re-expand. Plan your checkvalve, piston, seals, etc to have as little as possible dead space so the compressed air is pushed out the check valve, not left in a space to re-expand.

400 PSI is 27.5 bar. Compressing to only 20 bar won't get any out the check valve. It won't pump to 27 bar in the example given.

The above does not account for compression heating which does help get more through the valve.

actually, 20% is 1/5, not 1/20, so your max would be 5 bar. but the idea of deadspace is important.

Thanks.. got me.. 5 AM post.. Nightshift. I was thinking 20:1 and typed 20%.

Check valves are pretty simple if you've got a lathe.

There is one I modified to make it seal positively in this thread. Essentially I added an o-ring and a stainless (what I had) retainer sleeve for the o-ring. Cracking pressure is 3 psi.

http://www.spudfiles.com/forums/piston- ... ter,0.html

There is another check valve built into the base of the stirrup pump in the how to. (The pictures in the second half are still in the reverse order,...I have to remember to fix that.)

http://www.spudfiles.com/forums/easy-st ... ter,0.html

This could be greatly improved upon if you have a lathe.