Originally Posted by
HillRider
I have a Park PFP-4 pump with a dual head that had the same problem, it developed an intermittent leak through the Schrader side when I tried to inflate a presta valve.
When I took it apart I found the head contains a rubber ball about 1/4" in diameter that is positioned between the two valve holes and acts as a check valve. When you push a presta valve into its opening the stem is supposed to push the ball toward the Schrader side and block that opening and vise-versa. It didn't always seal but cleaning the ball and the ball seats pretty much ended the problem.
Actually what really ended the problem for good was substituting a Hirame presta-only valve head for the OEM one but that's another topic all in itself.
Hey, I have PFP-4 pump too. That one works fine so far. As for Topeak, FBinNY was correct that the problem was the Presta side; I had been focusing on shrader side since thats where air was escaping. I tried loosening the PV cap and that helped but didn't completely solve the problem -- reduced leak but still leak. So I removed cap, pulled gasket out -- looked fine, but as I was pressing it back into the head, I felt and heard a click; like something inside the head that wasn't seated properly, snapped into place. Put cap on, no more leak.