[cooperino]

In your first thread you say you purchased new ones. My question is, are they new? or rebuilt? I ask because when rebuilding you need to weld the tip back on after changing internal parts and o-rings. If this is not done with the finest of welds the valve would not bottom out correctly in the pump. Also, If the welder gets the valve a little too hot during welding it could begin to melt the new o-ring as well. This might cause it to work for a little while as you said but fail prematurely.