Pumping up bicycle tyres - what am I doing wrong?

I am a complete novice at bike tyre pumping.  Ashamed to say I have never done it before - I don't even own a bike.  Now need to sort out son's bike tyres as they've gone really soft, but I must be doing something wrong.

I have a pretty straightforward pump (I think).  I screw on the pump to the valve on the tyre, pump it up, then unscrew it.  But as I'm unscrewing, all the air seems to come back out, and leave me back at square one.  So what am I doing wrong?  I've tried loads of times, but I just can't get the pump off the tyre without losing air.

Have tried google, but there only seems to be much more advanced info than what I'm looking for.

Buy a track pump (google for pictures).  Lidl are doing special offers on bike stuff tomorrow and I think you can pick one up for a fiver.

Correction - offers start on Thursday.

http://www.lidl.co.uk/uk/home.nsf/pages/c.o.20090723.p.Floor_Pump.ar5

Sorry to be frighteningly dense, but how will that help?

I can see that a track pump is different looking, but other than that I'm clueless.

They clip into the valve and unclip quickly, plus it's far easier to pump up the tyre to the right pressure (a hand pump simply won't go it unless you're planning on entering world's strongest man).

Gotcha.  Thanks very much.  That makes sense.

 I'm assuming that I'm not doing anything wrong then - it's just that unscrewing the pump from the valve takes too long and lets air out as it's doing it.

I would agree with Baron on this...these pumps do make life much easier. I run my tyres at around 80-120psi and this is impossible with a standard pump.

One thing you have'nt mentioned is what type of valve the tyres have.....knowing this this may hold the answer to your problem and us being able to best advise......

Peter