A curious Zefal HPX issue

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ultraburner
Posts: 60
Joined: 20 Feb 2010, 4:27pm

A curious Zefal HPX issue

Postby ultraburner » 9 Jan 2020, 9:46pm

I have a seldom used, in fact I think I've pumped up three tyres with it Zefal HPX.

It let me down, no pun intended in a non spectacular way on a towpath in the middle of nowhere. I had retrieved it from its perch in my frame confident that it would get me up and running in jig time compared to those wee mini pumps.

Indeed I had somewhat sanctimonously used it on a chums bike the previous day with no issues.

Not on this day though everything started ok then any pressure that I generated was being forced back into the pump with the result, the handle fully extended and any air I had managed to inflate into the tube mysteriously disappeared.

A kindly passing cyclist saved my blushes with a minipump. :?

It was too cold and wet to investigate at the time but yet another puncture a couple of days later found me on the same position.

Has anyone else experienced this?

Brucey
Posts: 36763
Joined: 4 Jan 2012, 6:25pm

Re: A curious Zefal HPX issue

Postby Brucey » 9 Jan 2020, 10:10pm

you don't say if you were pumping presta or Schrader

if Schrader then the check valve in the pump has failed

If presta then the check valve in the pump has failed and you managed to hold the pump at a funny angle or something and thus jam the presta valve open. [NB with new seals in good condition, presta valves should not be 'held open' by a HPX pump. If you push the head too far over the valve, the seal wears double-quick and the valve jams open. Not good.]


You can service the check valve (it probably just needs cleaning, and you should try flushing it in situ first ) thusly

1) remove the piston rod from the pump
2) using a very long screwdriver (which can/must have a broad tip, ~2.5mm thickness, ~1/2" wide) unscrew the check valve assy.
3) fettle
4) reassemble

IME unless the chuck is kept well lubricated (ideally with silicone grease) the 'O' ring on the cam follower tends to wear or be damaged eventually. If small shavings of rubber appear in the mechanism, these can jam the check valve open, with effects much as you describe. If the pump is stashed somewhere on the bike where the chuck will get muddy, you need to fix that, else more bad things will happen.

FWIW you can make a tool to unscrew the check valve by using a length of 1/2" OD tubing. Simply cut the end so that two protrusions about 2.5mm wide remain; these ought to be enough to gain purchase (using mole grips or something on the other end of the tube) on the screw, provided the tube is held central in the bore of the pump.

cheers
Last edited by Brucey on 9 Jan 2020, 10:23pm, edited 1 time in total.
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freiston
Posts: 691
Joined: 6 Oct 2013, 10:20am
Location: Coventry

Re: A curious Zefal HPX issue

Postby freiston » 9 Jan 2020, 10:12pm

Could it be that the coupling of the HPX and the tube valve was awry and the valve had been forced open?

Edit - beaten to it!
Disclaimer: Treat what I say with caution and if possible, wait for someone with more knowledge and experience to contribute. ;)

rotavator
Posts: 269
Joined: 6 Jun 2016, 9:50pm
Location: North Wales

Re: A curious Zefal HPX issue

Postby rotavator » 9 Jan 2020, 10:15pm

It sounds as if the valve on your bike's tube was stuck open when you were trying to pump it up but it was unstuck and acting normally when the Good Samaritan took over.

However, I don't know anything about the Zefal HPX pump but I assume that it does not have a no-return valve in it.

Edit: also beaten by Brucey

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ultraburner
Posts: 60
Joined: 20 Feb 2010, 4:27pm

Re: A curious Zefal HPX issue

Postby ultraburner » 9 Jan 2020, 10:25pm

Should have stated, presta.

Now checked on various tubes all with the same effect. Sounds like this one way check valve may be the culprit.

Will disect and report back tomorrow.

Thanks for the pointers!

I'm scunnered but determined to resolve.

Brucey
Posts: 36763
Joined: 4 Jan 2012, 6:25pm

Re: A curious Zefal HPX issue

Postby Brucey » 9 Jan 2020, 10:31pm

NB even if the check valve in the pump has failed, you should still be able to pump presta valved tubes OK. If you can't, it means you have the pump connected to the presta valve in a way that jams the presta valve open. This is not correct, as described above.

[when I started cycling the most common pump had a barrel about 1" diameter and no check valve. Tubs were (with no small difficulty) often inflated to about 130psi. You soon learned not to jam the presta valve open, since otherwise the pump piston could fly out of the pump and travel about a hundred yards or so. If it didn't hit you in the stomach first, of course....]

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

MikeDee
Posts: 584
Joined: 11 Dec 2014, 8:36pm

Re: A curious Zefal HPX issue

Postby MikeDee » 10 Jan 2020, 3:42pm

Maybe that plastic piece in the chuck is oriented for Schrader and the valve is being jammed open.

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ultraburner
Posts: 60
Joined: 20 Feb 2010, 4:27pm

Re: A curious Zefal HPX issue

Postby ultraburner » 11 Jan 2020, 10:56am

Brucey called it.

It was the wee red ball jammed in place.

Visible after taking the top section apart. A quick poke with a sharp tool forced it back and then copious amounts of silicone spray.

Quick test confirms that was the problem.

Many thanks.