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Hissing sound coming out of bike valve?

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Hissing sound coming out of bike valve?

Old 02-15-14, 10:49 PM
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Hissing sound coming out of bike valve?

Hi all,

Every time I pump the flat tire on my bike, there's a hissing sound coming out of the valve. The valve is screwed on tightly but there's always a hissing sound. I don't know if it's a slow leak in the tube or something wrong with the valve?

There doesn't seem to be a hole in the tube either last time I checked.
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Old 02-15-14, 10:53 PM
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It sounds like the tube is bad, whatever the reason, but if you really want to track down where the hissing is, take the tube out, inflate it and submerge it under water. You will be able to tell where the leak is from the bubbles.
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Old 02-15-14, 10:54 PM
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The hissing is air leaking out someplace. If the tire is filling effectively, it's probably in the connection between the pump head and the valve. The fact that you're successfully filling the tire means it's not that bad, but you are working a bit harder than necessary. Possibly the pump head needs a new gasket, or you're not fitting it properly, but I can't diagnose from here.

If the tube is not filling the tire stays flat despite your efforts, it could be a problem between the pump head and valve, or the valve is leaking at the base where it joins the tube. You might try painting the pump head and valve with soap solution and see if you can blow bubbles to pinpoint the source of the leak.
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Old 02-16-14, 08:16 AM
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If this is a Schraeder valve, is the valve core screwed in tight?

Is this your first experience with a flat?
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Old 02-16-14, 09:08 AM
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It sounds to me that the connection between your pump's head and the Presta valve may be the source. I've seen some situations where tubes will be taking in air and bleeding a small amount at the same time. As long as you stay ahead, you'll get to the desired inflation, just with harder work.

Try fully inserting your pump on to the Presta valve and see if that makes a difference. Some tubes have longer valve stems and require you to more fully insert the head on the valve. Just for kicks, before you put your pump head on the valve, press down the Presta valve a little and see if it's a bit gummed up. They sometimes need a drop of lube themselves. Might not solve your problem, but it won't hurt anything either.
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Old 02-16-14, 09:28 AM
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Not infrequently you can get intermittent leaks where the stem meets the tube
It will kinda seal-but will obviously leak-hiss-when a pump head is on it and your "bending" the stem
Frankly I doubt this is the current problem
Put your ear down there -see if it is coming out of the pump head valve connection-or from the rim hole
You should be able to hear and feel the difference
Bend the pump head stem connection- any hissing?
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Old 02-16-14, 09:43 AM
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Ether the valve stem or the tube... or the area where the stem connects to the tube... you got a leak. Replace the tube then track down the leak to see if the tube is repairable. Fill the tube with a bit of air pressure and slip the stem under water to see where the air bubbles out.

A common air loss flat is damage/wear around where the stem attaches to the tubes body. This is often caused by pulling off the pump from the stem.... pulling the stem to the rim. If that is the case here... you can resolve the sticky pump pulling problem.

First put a tiny dab of light/white grease in the pump head. Then if you didn't put the threaded washer on the valve... do that now (but don't screw it tight). Then if the pump head sticks to the valve... slip a small wrench between the washer and the pump head. Hold the wrench firmly with one hand... but don't press the wrench/valve into the tube. With the other hand pull the pump head off against the wrench... and not the valve/tube.

I keep a small combination wrench tied to my pump.

Last edited by Dave Cutter; 02-16-14 at 09:49 AM.
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