the flat that isn't punctured....?!??

PBo

Repaired a puncture.

Slowly went flat again.

Checked it - couldn't find a thing.

Reinstalled tube. went flat.

Replaced tube - checked old one - still no puncture to be found! Blew it up, and left it overnight - no noticeable deflation.

WTF? Any ideas? (i've pushed the valve in and out a few times in case there was some sort of blockage....)

ta

plowmar

Could be valve when under pressure.

You do not say when leaving tube overnight wether or not it was back on wheel, but assuming it wasn't then there would be very little pressure in tube to vent air through valve, when in tyre and therefore restrained higher pressure = deflation. (Boyles law ?)

No other logical explanation.

tywin1

Could be the valve needs tightening if its schrader?

wgwarburton

tywin1 wrote:

Could be the valve needs tightening if its schrader?

...or a Presta with a removable top (Schwalbe, IIRC). If it has flats at the end, try using them to tighten it. I suppose there could be grit in the valve, I remember reading that you should tap a Presta ("pshht!") to blow any debris out of the way before pumping to top up the pressure.
Otherwise- "pinhole" puncture that's leaking slowly when under pressure. You could try removing the patch and redoing it but in your shoes, I think I'd probably decide that the failed repair was enough to write off the tube. Not worth the hassle of fixing it again.

Cheers,
W.

The Rookie

I had a patched tyre that then went down, tested and leak was at patch, when fiddling with it it mysteriously sealed itself and hasn't leaked since! I've also had valves leak slightly due to muck (I assume) as after reinflating (presumably blowing the muck into the tube) it was fine.

I also had a tube that didn't leak when inflated out of the tyre, I ended up having to 'balloon' it to get it to leak through the tiny pinprick hole enough to find.

Simon

Fireblade96

the old-fashioned approach of removing the tube, inflating it and sticking it in a bucket/bath (delete as allowed) of water is fairly definitive in showing where any air leaks are coming from.