track pump head question

[velosam]

I know I am probably being really thick but hear me out.

I have a bontager track pump. When I go to inflate my tires, I undo the valve bit and then put the pump head on. Unfortunately for some reason this just manages to deflate the tire.  The valve in the pump seems to move up and down so I cant figure out what is wrong.  The only thing I did was to unscrew and then refasten the plastic cap that holds the valve in.

How do I fix this, if at all?

The pump in question is this

https://www.evanscycles.com/bontrager-charger-pump-00104765

thanks

[Ben T]

you do know the pump head should start off perpendicular to the spokes, i.e. as it is in the pic in the link, and the 'clamped on' position is with it parallel to the spokes - not the other way round.

[velosam]

Good point but yes. Pull up the lever when the pump head is on. What I am not sure about is, that it pops off when the lever is upright or not!!

[JonB]

Sounds like you're not pushing it on far enough, with mine (not Bontrager) I can get a bit of air release as I push it on but keep pushing and the air stops releasing as the inner valve is no longer being pushed down by the pump head at that point you can use the lever to lock. I find it works best if you undo the presta valve a good few turns (I presume the pump head is set for presta?).

[Ben T]

Check the spring in the valve is intact - i.e. does it hold air with it unscrewed. Usually does but I have seen tubes with the spring gone so air gushes out as soon as you unscrew.

Also do both of the same pump on different tube/wheel, and different pump on same tube/wheel tests, for diagnostic reasons.
Only then will you be able to conclude whether it's pump, tube/valve, both, or neither.

[Brucey]

some presta valves have inserts that screw into the valve stem. If the insert is loose, just unscrewing the dustcap just unscrews the insert and the air comes out of the tyre. Could this be happening ?

If you mean you unscrewed the parts from the pump head itself, then anything can have happened, before or after there was a problem.

IME pumps that 'conveniently' do more than one valve type commonly succumb to some trivial problem or another; the heads are more complicated than they need to be.

cheers

[Somnolent]

Is this a problem that has existed from new, or something that has just happened after a period of successful use?

My Joe Blow Sport has developed a similar sounding fault after several years of use.
Seems to be some sort of non-return arrangement in the innards that has failed.

[rafletcher]

Sounds like you're not pushing it on far enough, with mine (not Bontrager) I can get a bit of air release as I push it on but keep pushing and the air stops releasing as the inner valve is no longer being pushed down by the pump head at that point you can use the lever to lock. I find it works best if you undo the presta valve a good few turns (I presume the pump head is set for presta?).

This sound right

[Torslanda]

That last point is relevant. I take it that when you lock the lever it actually grips the valve stem?

[velosam]

Will try and push the head down more!!!  Will have a go after tomorrow as there seems to be enough air to get me to work and back.

I think it grips the valve stem - however it may not as I have to use the pump with the valve stem south I.e pointing up as otherwise the head falls off (if the valve stem is at the top of the wheel).

Yep Presta valve.

[zigzag]

if it falls off when locked it's definitely not gripping tight enough. my favourite position of the valve when inflating is around nine o'clock (or just below a mudguard).

[LittleWheelsandBig]

Bring it round and we'll check it out together. I need to unstick a faulty non-return valve on a Silca track pump too.

[Crepello]

I bought a Phaart track pump a while back for use as an emergency pump at my mums' house. So just when I needed a quick getaway, I went to pop the pump head onto the valve, which completely deflated the tyre.

I could see that the rubber collar inside the valve head had been set up for schrada valves, so i dug that out and flipped it round for presta (a narrower fit), went to insert the head onto the valve again and it just falls off. Several times. Well I could see that lifting the lock lever was pushing a centre pin downwards inside the head and this was causing the head to push off the valve. I took the head apart again and flipped this centre pin around, put it back together and VOILA! it worked.

[Gattopardo]

Replace pump head with a decent one. 

My bontranger one broke, so I replaced the pump with a lidl track pump.

[LittleWheelsandBig]

The plastic pump head was dismantled, the hose slightly shortened and overly-textured surfaces were smoothed out. The pump seemed to be coping easily with delivering 100psi after that.

[Brucey]

result!  A little judicious fettling works wonders!

cheers

[velosam]

Big thanks time to Littlewheelssmall and big for sorting it.