Linear piston air pump loses pressure over time?

[a date with nature]

So i recently got a linear piston air pump from my grandpa. finally got it hooked up to all the sponges today and turned it on. At first, it works perfectly, i even had to open a few bleed offs. i come back ten or so minutes later and all of them have lost a significant amount of pressure, a few of them had even stopped completely. I checked the taps, all of them were on full blast. I checked all the joints in my pvc, the hose from the pump to pvc, etc. I felt the pump and it was pretty warm, but not burning me by any means. I turned the pump off and then back on about ten minutes later, and the exact same thing happened, I'm thinking it has something to do with it's warming up. But i thought that was something it was expected to do? What am i supposed to do? any suggestions?

[jwcarlson]

I do not know what the inside of one of these pumps looks like, but it sounds like it could be a clearance issue once things get warmed up.  So if there's a seal on the piston (which I would assume there is, or maybe a diaphragm), it could be that when it's cool, the seal/diaphragm is working alright.  But as soon as it gets to operating temperature, it's no longer sealing well.  I think there's also check valves kind of built into the construction of these and those could be similarly affected by the temperature.

You could look into seeing if you can locate a rebuild kit.

Edited January 2 by jwcarlson

[tike]

Check out some of the maintenance videos on youtube and see if that helps the problem.