Originally Posted by
recursive
QFT.
I have devised a procedure to figure it out for real though. Repeatedly remove and replace the pump head from the valve stem, taking a measurement each time. Do this at various pressures. After your data is collected, you can calculate the average pressure lost as a function of temperature and beginning pressure.
Easy.
The problem is that you're also measuring the amount of air lost when you replace the pump head. There's no way to know how much of your measurement is from replacement vs. removal. I think a VERY small amount is lost from removal, and almost all of what you're seeing is from replacement.
Also, with my pumps, attaching the head doesn't pressurize the pump since it's at a lower pressure than the tube. So I lose some air getting the thing attached, but I have to pump it a bit to equalize the pressure and get a reading. If you're provides a reading upon connection, then you're pressurizing the pump with air from the tube, which lets air out of the tube. Inconsistencies with this process will also greatly affect the measurements.
The real way to do this would be to set up a rig made from PVC with a pressure gauge attached to it. Then pump it up to 100psi and see what happens to the fixed gauge when you remove the pump.