Help! Tyre deflating after being pumped up.

[dodd82]

Hi all

I've arrived at work this morning, and decided to pump my tyres up so that I don't need to do it before I leave later.

The front is fine, but after pumping up the back tyre and removing the pump, the tyre completely deflates.

It has been missing a cover for the bit where the pump goes on as the last one broke, and I am waiting for some spares to arrive in the post.

Any ideas what might be causing it to deflate, and what I can do about it, so that I can get home?!

Thanks!

 

[Nathjh]

I only pump up mine in emergencies now. After last time I decided to treat mine to a topup I managed to split the tube at the valve where it was wobbling about hope this isn't the case for you. Don't know why else it would happen sorry...

 

[MossCommuter]

Has the valve core come out/loose? (they screw in)

http://k0lee.com/wordpress/wp-content/uploads/2009/10/presta-valve-11.jpg

 

[compo]

Has the valve core come out/loose? (they screw in)

http://k0lee.com/wordpress/wp-content/uploads/2009/10/presta-valve-11.jpg

The same also applies to Schrader (car type) valves. The cores can come loose. A tweak up with a valve key usually cures it. A blob of spit on the valve will create a bubble if air is escaping.

 

[dodd82]

When I put the pump back on, it pumps up again and holds the air.

It's only when I remove the pump that it deflates?

 

[grumpyoldgit]

Deffo a valve problem,which type is it?http://sheldonbrown.com/brandt/presta-schrader.html

 

[Cubist]

Then it does sound like a valve problem. What sort of valve is it?

 

[dodd82]

I'm not 100% sure but from the pictures I'd say a Schrader valve.

Hope there's a way it can be easily fixed?!

Thanks for your help guys.

 

[compo]

If a schrader any car shop or Halfords will sell you a valve tool that has a key on it to tighten the valve core. They are very cheap. You can also buy new cores for a few pence and the simply screw into the valve body. Also with a schrader valve, what happens if while you pump up the tyre you let go of the pump handle. If the valve core is leaking it can push the pump handle out as the air leaks into the pump body.

 

[Davidc]

Some dust caps (car and bike) have a valve key molded into the top (two little prongs) which will tighten it back in. If not a pair of long nosed pliers can be used (with a little care).

The valve bit that screws in has 2 little prongs sticking up, one either side, which are where the (small) tightening force needs to be applied.

And what compo says

 

[sidevalve]

If it's a shrader borrow a valve cap from a nearby car [it would be nice to ask of course]. Most workmates would lend a valve cap to get you home, [if not I'd try finding some new mates].

 

[dodd82]

If a schrader any car shop or Halfords will sell you a valve tool that has a key on it to tighten the valve core. They are very cheap. You can also buy new cores for a few pence and the simply screw into the valve body.

Thanks. So is that a case of just applying a key to it whilst it is on the wheel, or do I need to take it apart?

 

[Davidc]

On the wheel

 

[dodd82]

If it's a shrader borrow a valve cap from a nearby car [it would be nice to ask of course]. Most workmates would lend a valve cap to get you home, [if not I'd try finding some new mates].

So put the cap on after I've pumped it up?

As soon as I take the pump off, the air shoots out!

 

[compo]

Thanks. So is that a case of just applying a key to it whilst it is on the wheel, or do I need to take it apart?

All the key is is a thin hollow tube with a couple of slots in it to locate on the valve core. There is no need for any dismantling, simply insert the key aad turn it until you feel it locate then just turn it to tighten the core. Same procedure to change the core, unscrew the old one and it will drop out and screw in the new one.