Help: tube valve issue

My 36" foss tube starts leaking as soon as I connect the pump. I can only pump so fast that the inflation balances the deflation, resulting a net zero psi increment. The tube does not leak if I remove the pump, and the pump is proved working well on other tubes. So I guess it’s due to a faulty valve?

I can change the tube as the last sort but I’d like to see if there is an easy way to get it fixed first. Thanks!

Maybe the problem is with the pump? Try a different pump. If it’s the same, the only option I see is to use a valve wrench to tighten the pin in the middle if it’s loose. But I don’t think it’s the problem, then the valve would always be leaking. I’m assuming it’s an AV valve ? Otherwise I wouldn’t waste my time and thought but buy a new tube.

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Thanks! Yes it’s a schrader valve. I’ll try another pump, although this one works well on my other unis.

The connection between the pump hose and the valve stem is leaking. You are trying to pump a tube with a Schrader valve using a pump hose that has a Presta fitting or you have not tightened the hose connector to make a leak-tight fit with the valve stem.

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Today as I tried again the valve magically healed itself. It’s still a bit leaking, but I can easily outrun it. I guess something was loose, and now it’s tightened a bit either by the vibrations of my ride yesterday, or contraction from temperature change. Still I think it will come back, but it’s good for now.