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Old 02-23-11, 04:29 PM   #1
DOS
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My Topeak Twinhead leaks

I have a relatively new twinhead on my Topeak pump (6 months). It worked fine at first but now leaks when using it on presta valves. Specifically, when pumping, air escapes out of the schrader side. Its not that big a deal because air still goes into the tire, and if I put my thumb over the schrader side, I get a pretty reliable pressure reading on the gauge. Its just annoying. I made sure all the caps are tight, and I happened to have twinhead rebuild kit so I replaced all the seals; still it leaks. It does not leak when using it on schrader valves. ANy other troubleshooting tips would be appreciated.
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Old 02-23-11, 10:56 PM   #2
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The thumblock lever in the head doubles as a diverting valve. When the lever is locked it opens the air path to the used end and closes it to the unused end.

Possibly the valve seat or O-ring are nicked and leaking. Or you have the PV end cap too tight so you can't throw the lever to the end of the it's stroke when you close the thumblock and it's still leaving the diverting valve open slightly to the unused end.

Before taking it apart again test the head by closing the lever all the way as if for a PV, then blocking the hole with a pencil point and seeing if any air leaks out the back. If not you're OK and just need to adjust the PV gasket so you can close the lever far enough.
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Old 02-24-11, 05:28 PM   #3
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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.
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Old 02-24-11, 06:27 PM   #4
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Quote:
Originally Posted by HillRider View Post
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.
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