inflating tyres
 

Hi,

I've been given an old bicycle for my son to use. When I inflate the tyres they go up fine, however as I unscrew the pump from the valve all the air escapes from the tyre. The bicycle has a Schrader valve and I'm using a pump like this :
http://www.halfords.com/webapp/wcs/s...egoryId_165661

Do I just need to replace the valve or inner tube? Should I get a better pump?

thanks in advance (from a noob)
Mike

Mike, Could be either the tire or the pump. I suspect the pump design if you're having to unscrew it as there really isn't much air by volume in a bike's tire. A floor pump with a clamping device is a better choice for home maintenance.

Brad

Hi,

I know the pump. You have to undo it off the valve as fast as possible.
There is nothing wrong with the valves in your tubes. Its a crude pump.
You will always lose some air getting it off, you need to be quick.

Its a crude modification of a pump designed for Dunlop valves to
work with Scraders. The latter the valve needs opening by force
whilst a Dunlop doesn't. Pumps better designed for Schraders
have a lever to open and shut the Schrader valve.

http://i.ebayimg.com/t/Mini-Portable...+Bg~~60_12.JPG

Yuo can get these from a £1 or 99p shop. The lever is pulled out to open the valve
and pump up the tyre, you close it before removing the pump. Therefore no air loss.

rgds, sreten.

All car foot pumps have the lever for Schrader valves.
The lever at the same time compresses a rubber bung onto the valve thread locking it.

Many thanks for your responses ;)

If the air is escaping as you unscrew the pump, but the valve holds whatever's left when your done, it's neither the pump or valve, but an unfortunate combination of the two.

Pump heads (hoses) have a valve depressor that opens the valve so air can flow. If the valve stem or depressor are high the valve opens before the gasket seals the top of the tube, so air can leak out. The fix is fairly easy. Add an O-ring or rubber washer to the gasket, so the seal happens sooner, and releases later with respect the valve being open.

Go to the hardware store and buy a 5/16" (8mm) OD O-ring, and drop it into the pump head, and things will get better. Toy might have to tighten the head on hard to compress the O-ring enough to engage the valve depressor.

Question, perhaps I'm just not reading this right, does the air CONTINUE to escape after the pump is released from the tube? If so it sounds like it may also be a stuck or loose valve core. You can get a valve core tool nearly anywhere, I got mine with a pack of replacement cores. Place the tool inside the stem, interlock the core and try and tighten it gently, if it moves much at all then it was loose, try pumping again. If it holds now it's fixed, if it leaks again try replacing the core. Unscrew the core with the tool and remove it and replace it with a new one. If it still gives you issues then it must be damaged somehow. Could it be a tear in the tube near the stem?

Hi,

I dug out the pump I have. Following FB's fix :

I moved the rubber ring on the other end of the
"hose"into the "head" and improvised a washer
for where the hose attaches to the pump.

It did work a lot better in terms of the amount
of air lost as you take it of the valve.
Not a lot of thread goes onto the valve though.

rgds, sreten.

TBH I think the pump is too cheap. The part that
allow the head to spin on the hose disintegrated
on mine with only a few uses. Its only usuable
now because I glued up the head to the hose.

Maybe being hamfisted on my part but cross
threading is something you need to be careful
to avoid, otherwise then its almost inevitable.

With it all working its very hard to get decent
pressure, its useful for completely flat though.

The £1/99p minipumps are much better IMO.

You don't need lits of threads to hold the head on since there's virtually zero load. One to two turns will do it. If needed add another O-ring or gasket until the valve depesser pin is below the rim of the gasket, so it seals before opening the valve, and unseals after the valve is closed when removing.

Yes, it is a cheap and not so great oump, and I wouldn't suggest buying on. But once you already have one, spending a few pence to make it work makes sense.

the air escapes as I unscrew the connector to the valve, once it's off the air stops escaping (but the tyre is virtually flat). I'll pick up the other kind of pump this week and try that, otherwise I'll look at replacing the inner tube. It's quite an old bike, wouldn't be surprised if it was a bit knackered

once again, thanks for all the responses - much appreciated ;)