Slow puncture which doesn't show under water

[LittleGreyCat]

I have an old inner tube replacing one which was punctured by a thorn.
Different tyre so the original thorn isn't an issue.
They tyre slowly deflates over a couple of days.
I've just taken the tube out, pumped it up slightly, and then submerged it bit by bit in the kitchen sink.
There is no tell-tale stream of bubbles from anywhere?
How might I diagnose?

I note that if the problem was with the Presta valve then water might have got in to lubricate the valve rubber and stopped the leak for the moment.

Anyway, I have new inner tubes so I shall fit one of those and see how it goes.

[Eyebrox]

Put more air into the tube and the hole will be eventually become apparent when the tube is squeezed under water.

[mig]

are you checking the valve?

[Nearholmer]

Sometimes it’s a valve leaking so slowly that it is agonising waiting for a bubble to eventually form.

[2_i]

Sometimes it’s a valve leaking so slowly that it is agonising waiting for a bubble to eventually form.

Yes, but such a leak deflates the tube over weeks, not a couple of days. To see the bubbles coming out, wipe any bubbles left from submerging the tube and wait for any new bubbles to form.

[wjhall]

Gave up using water long ago, there always seem to be too many bubbles stuck on the tube to eliminate.

I have usually found that leaks can be detected with a reasonable pressure in the inner tube, but not enough to explode it, by listening, looking and holding the tube close to a sensitive part of my face, cheeks or lips for example. But I suppose there must be punctures too slow to be detected that way.

However I do confess to a so far undetected slow puncturing tube hanging up in the garage. I suppose I should now go and apply my own advice again. I suppose that points to another solution - forget about it, concentrate on feeling the inside of the tyre to detect anything stuck in it. After that put some sealant in the tube and hope it seals the hole.

[mattheus]

I have usually found that leaks can be detected with a reasonable pressure in the inner tube, but not enough to explode it, by listening, looking and holding the tube close to a sensitive part of my face, cheeks or lips for example. But I suppose there must be punctures too slow to be detected that way.

I've just found one of these! ;-P

It wasn't easily visible even in the bath, but the evidence says it's letting enough air out to deflate inside 24h. With the tube out of the bath and dry it was vv near impossible to see the hole. Absolutely no way I could hear it.

Incidentally I find these very slow leaks to only be caused by thorns (which are mainly on my commute, being a typical Sustrans excursion). The majority of my flats are from flints - anywhere in Europe - and they are always much faster.

(the above was part of a batch of 4, all patched on Sunday afternoon. So a much "welcome" chance to make comparisons! )

[Paulatic]

I've just taken the tube out, pumped it up slightly, and then submerged it bit by bit in the kitchen sink.
There is no tell-tale stream of bubbles from anywhere?
How might I diagnose?

Blow it up til it’s thicker than your arm.

[slowster]

Wiggle the valve from side to side and forwards/backwards. Sometimes that is necessary to open up a small split around the base of the valve sufficiently for air to be able to escape through the hole.

[wjhall]

In fact I had a fairly slow puncture on Friday, it first went down over about 20 min, reaching the stage where I could feel little bumps in the road, then stayed up for an hour and 20 km after I pumped it up, and then a further hour taking the train home before becoming noticeably softer. The hole was a pin prick, took a while to find, but detection was helped by the bright green colour of the sealant in the pin prick. So a further suggestion: put some bright coloured sealant in and see if that makes the hole obvious.

The other indicative factor on that one was finding the cause of the puncture in the casing, something very thin, by feel, which narrowed the search area.

[andrew_s]

Blow it up til it’s thicker than your arm.

This is the answer.
If the tube is blown up to treble the thickness, the hole will be stretched to 9x the size, leak much faster, and be fairly easy to find.

The only thing to watch for is that the tube inflates evenly. If you get a bubble growing at one point, it's a weak spot and the bubble will burst before the thinner bits of the tube are stretched enough to show the leak. It that happens, give up on over-inflation and revert to alternative methods.

[pwa]

I've just taken the tube out, pumped it up slightly, and then submerged it bit by bit in the kitchen sink.
There is no tell-tale stream of bubbles from anywhere?
How might I diagnose?

Blow it up til it’s thicker than your arm.

Yep. Make it far bigger than it gets when in use. Then look for the leak. Personally, if it turns out to be the valve, I would ditch it, unless it is just a case of screwing the valve in a bit harder.

[pjclinch]

Sometimes it’s a valve leaking so slowly that it is agonising waiting for a bubble to eventually form.

Yes, but such a leak deflates the tube over weeks, not a couple of days.

Usually, yes, but when I got a new bike back in May the tyres were going noticeably softer over a couple of days and it turned out to be the cores in the valves were not in quite as tightly as they should have been!
These were also failing to show any leakage stream when submerged.

Pete.

[Barrowman]

Might be a grandmother/egg situation...

Did you remove the thorn after the initial puncture? (A few of my CUK colleagues have fallen for this, including me once)

If it's a pin prick as has already been suggested ,you will have to approximate the pressure when it's inside the tyre ( which will render it surprisingly large when not constrained by the tyre) as has already been suggested.

[sjs]

I've just taken the tube out, pumped it up slightly, and then submerged it bit by bit in the kitchen sink.
There is no tell-tale stream of bubbles from anywhere?
How might I diagnose?

Blow it up til it’s thicker than your arm.

Then throw it away and buy another one.