Phantom flat

[Morzedec]

Mick, your tube must be the only thing in Gunnislake that is flat ........................

Happy days,

[Mick F]

Out for a ride on Thursday. 27miles and 3,270ft of ascent.
That's 121ft per mile!

[Brucey]

.... connecting and disconnecting and doing nothing else, will deflate the tyre.

Pressure gauges included in this, but the Topeak Twinhead was terrible.

The Lezyne Airbleed unit is foolproof and doesn't deflate the tyre.

............. from actual experimentation.

I repeat, the Topeak Twinhead was terrible. It worked well as a connector, but the unit releases air each and every time you disconnect and far worse than a good quality pressure gauge.

I repeat, only if you push the thing on too far.


FWIW there is only a short list of things that can cause phantom deflations

1. Grit or debris in the valve causing it to leak (*)
2. Presta valve locknut not tight
3. Valve core not tight in valve stem; sometimes they don't have to move much in order to leak.
4. A problem at the joint (be it mechanical or bonded) between the valve stem and the tube
5. A patch (or other joint in the tube) which lifts, lets the air out and then reseals
6. A hole in the inner tube which is small enough to seal itself (eg with the object that caused it still in the hole)
7. A hole in the inner tube which is small enough to seal itself depending on exactly how the inner tube is refitted; e.g. if the hole is in part of the tube which is pressed hard against an intact part of the tyre, it may make almost perfect airtight seal

(*) NB It is always a good idea to let a little air out of a presta valve before connecting a pump to it. This both ensures that the valve is not jammed shut, and ensures that any grit in the valve is blown outwards and doesn't get a chance to foul the valve mechanism.

cheers

[Mick F]

I repeat, only if you push the thing on too far.

Utterly agree.

It needed to be "too far" to stay on when pumping to 120psi.
Bought new seals, and it was the same.

I don't think I still have the Twinhead, but when I'm next in the shed, I'll have a look.

FWIW there is only a short list of things that can cause phantom deflations

1. Grit or debris in the valve causing it to leak (*)
2. Presta valve locknut not tight
3. Valve core not tight in valve stem; sometimes they don't have to move much in order to leak.
4. A problem at the joint (be it mechanical or bonded) between the valve stem and the tube
5. A patch (or other joint in the tube) which lifts, lets the air out and then reseals
6. A hole in the inner tube which is small enough to seal itself (eg with the object that caused it still in the hole)
7. A hole in the inner tube which is small enough to seal itself depending on exactly how the inner tube is refitted; e.g. if the hole is in part of the tube which is pressed hard against an intact part of the tyre, it may make almost perfect airtight seal

(*) NB It is always a good idea to let a little air out of a presta valve before connecting a pump to it. This both ensures that the valve is not jammed shut, and ensures that any grit in the valve is blown outwards and doesn't get a chance to foul the valve mechanism.

All good advice.

[NATURAL ANKLING]

Hi,

I repeat, only if you push the thing on too far.

Utterly agree.

It needed to be "too far" to stay on when pumping to 120psi.
Bought new seals, and it was the same.

I don't think I still have the Twinhead, but when I'm next in the shed, I'll have a look.

I see now, the pump valve head was rubbish, and you used it incorrectly

[Mick F]

I used it in the ONLY way it would work to get enough air pressure into the rear tyre.
I experimented until I was blue in the face!

Maybe mine was defective in some way.

[NATURAL ANKLING]

Hi,
Mick, We share a similar flaw
I hate abandoning things until I can get them to work, even if that means filling the house with useless devices

[philvantwo]

Had mine for about 8 years now, never had a problem with it. When you take the hose off the blast of air is from the hose, not the innertube. You did slide the lever across?

[Mick F]

The Twinhead had to be pushed on far enough for the locking mechanism to secure the rubber seal so when the pressure increased it didn't blow off.

With a Presta valve, the top end is narrower than the shaft. Where the Twinhead was supposed to go on, was at the narrow portion just below the valve ...................... that you have to unscrew first.

The Twinhead had to be positioned onto the the parallel shaft below the narrow bit to secure it to withstand 120psi plus.

By having it there, the Presta valve was depressed a little bit.
That was fine when inflating, but when releasing the Twinhead, air was released due to the valve being depressed.

PLEASE believe me, I did lots of experimentations to prove what I was finding.

[Mick F]

25-559-26-x-10-inch-inner-tube-with-40mm-presta-valve-light.jpg (7.98 KiB) Viewed 213 times

[philvantwo]

More than likely you've contaminated the valve with grease!