shock pump that does not lose air when you unscrew

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  • shock pump that does not lose air when you unscrew
  • wiggles
    Member

    Pump it 20psi higher than you want before taking the pump off.

    Premier Icon scotroutes
    Subscriber

    It doesn’t.

    The air you hear is what is trapped in the shock pump/hose.

    When you reconnect it, the air from the shock has to fill that space again – hence you appear to have lost pressure in the shock.

    Premier Icon mikewsmith
    Subscriber

    What he said, or buy a normal shock pump new that does the same. How did you measure the 20psi loss?

    toys19
    Member

    Scotroutes, I understand that, but in this case it actually does I promise. I have a £70 digital gauge that is repeatable and testable that shows it does.
    The pump works fine on my rp23, but not on my marz forks.

    khani
    Member

    Try one of these, it stops any air loss from the pump..

    toys19
    Member

    There are lots of pumps that advertise the no loss feature, I just wonder if anyone has got one that they know works good.

    Khani, thats a good idea cheers, will try that.

    mikey74
    Member

    There are lots of pumps that advertise the no loss feature, I just wonder if anyone has got one that they know works WELL.

    I use this:

    http://www.wiggle.co.uk/topeak-pocket-shock-dxg-shock-pump-with-gauge/

    It works.

    johnners
    Member

    The pump works fine on my rp23, but not on my marz forks

    Maybe not the pump then? Could be something shonky about the Marzocchi valve.

    Pete B
    Member

    On a standard shock pump the idea is that during removal the shock valve closes before the pump/valve seal is broken. The air you then hear escaping is that from the tube as the seal is broken.
    Maybe on the Marz fork the valves release pin is longer meaning the pump/valve seal is broken before the valve seats allowing shock air to escape.
    Something like the Topeak DX might solve this.
    Bugger! This is the internet – it definately will solve it regardless of any lack of proof!

    Junkyard
    Member

    Topepak
    IME some valves can stick and release air as you unscrew though in theory it should just be air from the pump.
    Toppeak removes this issue and is not much more expensive than other pumps

    toys19
    Member

    My lovely Marzocchi 55Cr forks take a normal shock pump (as opposed to the old marz special adaptor thingy.
    The only problem is that with my shock pump (an old progressive one that came free with my bullet frame, remember those days, something free with a frame purchase…) is that it releases about 20psi every time I unscrew it..

    Any recommendation for a lossless release pump?

    toys19
    Member

    cheers peeps. Appreciate your exp.

    coatesy
    Member

    I recently bought an SKS USP for workshop use, it has a two stage adaptor to limit air loss, might be what you’re looking for if you can find one (they’ve just been discontinued). Very nicely made, head and shoulders above all the other shock pumps i’ve worn out over the years.

    bencooper
    Member

    I use a DT one – it has an outer barrel that screws onto the valve, and an inner pin that pushes the valve open. So you can close the valve before undoing the outer barrel, so it doesn’t lose any air.

    I got a cheap shock pump off ebay for about a tenner. It has a second screw that screws in a pin that pushes the valve open. So you screw the pump onto the valve then screw in the second screw that pushes open the valve, pump your shock to your desired pressure, then release the second screw to close the valve and release the main screw where you do get a release of air from the hose. Works a treat. Aren’t they all like that?

    Maybe on the Marz fork the valves release pin is longer meaning the pump/valve seal is broken before the valve seats allowing shock air to escape.

    I had this on the piggyback on a Marz Rocco shock. Pump would dump the air and impossible to pressurise. Ended up removing the core and grinding down the valve core pin.

    STATO
    Member

    Scotroutes, I understand that, but in this case it actually does I promise. I have a £70 digital gauge that is repeatable and testable that shows it does.

    There is no way your pump can be releasing only 20psi every time it is removed, if it were losing pressure the amount lost would depend on how fast you unscrewed it. As has been said the design of the pump should prevent any air being lost from the fork/shock chamber, the air released is the pressure in the pump.

    If your clever gadget is showing a 20psi difference to what you pumped it to, then the gauge on your pump is wrong.

    toys19
    Member

    Thanks for your wisdom STATO.
    To test the pump I have done this numerous times:

    1)apply gauge to fork, reads 100psi.
    2)take gauge off
    3) put gauge back on reads 100psi
    4) apply pump to fork, reads 100 psi
    5) take pump off fork
    6) apply gauge to fork reads 80psi
    7) apply pump to fork reads 80psi
    8 ) pump fork back up to 100psi
    9) remove pump
    10) apply gauge to fork, reads 80 psi
    11) take gauge off
    12) put gauge back on, reads 80 psi

    johnners
    Member

    So just put in an extra 20.

    You’re welcome.

    toys19
    Member

    Johhners, whilst this may seem like a good idea, unfortunately its not 20 every time, varies from 10-30.
    It does seem to be to do with how fast I unscrew, but its still not a good system, no matter how fast I do it I still lose a lot of air.
    It must have been a problem found by other people hence the demand in the market place for these types of valve connector.

    Premier Icon scotroutes
    Subscriber

    It must have been a problem found by other people hence the demand in the market place for these types of valve connector.

    Want to buy some homeopathic “medicine”?

    Premier Icon Northwind
    Subscriber

    I use Beto ones, they’re really good, and inexpensive. But you’ve got to wonder if a change will help here, since it’s presumably the fork not the pump. I’d do as Gravity Slave suggested myself.

    Premier Icon johnhe
    Subscriber

    The Pressure Rite connector looks worth a try.

    Suggsey
    Member

    The Topeak one is great and is identical to the Cane Creek pump. No air loss at all but I’m not totally convinced on the accuracy of the gauge! I feel it may be reading over or my old rockshox one is reading under or my old marazochi one is reading under too. For the price you pay for these items I think they should come with a calibration certificate of accuracy.

    Premier Icon Northwind
    Subscriber

    The actual accuracy doesn’t matter much as long as it’s repeatable, unless you use a bunch of different pumps

    oldnick
    Member

    Try changing the valve core, they are just bog standard car ones.

    I got a handful for free just by asking at the local tyre place.

    Premier Icon Rusty Spanner
    Subscriber

    Wrong thread.

    Pump it up 30 psi too high then release air with the gauge until its at the pressure you want.

    petrieboy
    Member

    You lose the pressure when you reconnect the pump not when you disconnect it.

    trail_rat
    Member

    “It must have been a problem found by other people hence the demand in the market place for these types of valve connector.”

    Or and invention made to sell to the gulible.

    What petrieboy said.
    Perhaps the OP might have an issue with his shock but most people who buy these special shocks are very gullible.

    abductee
    Member

    You lose the pressure when you reconnect the pump not when you disconnect it.

    when you connect the pump it has to fill the hose up to the same pressure as the reservoir. This will cause a small amount of air to be lost. This air will be lost even with a zero loss connector. On the other hand it could be the rubber seal compressed and leaking before the valve is released.
    These have a zero loss connector
    http://www.rutlandcycling.com/101662/products/raleigh-shock-pump.aspx

    Premier Icon Speeder
    Subscriber

    The one that used to come with Magura forks used to have a clever valve so you could release the valve ore before unscrewing the pump – not sure if they’re available separately though. Been watching eBay for one for ages and they jut don’t come up.

    I do believe the pressure drop theory as on a valve that imply unscrews there’s nothing to stop air escaping as you unscrew.

    STATO
    Member

    I do believe the pressure drop theory as on a valve that imply unscrews there’s nothing to stop air escaping as you unscrew.

    There is, the pump head has a seal. As you unscrew the valve on the shock is closed before the seal on the pump is broken. So in effect you have 100psi is the fork, sealed, and 100psi in the pump which will be released when you finally unscrew enough to break the pump seal.

    Im the OP case it could simply be the pump is old and the o-ring seal is not holding pressure like it should.

    1)apply gauge to fork, reads 100psi.
    2)take gauge off
    3) put gauge back on reads 100psi
    4) apply pump to fork, reads 100 psi
    5) take pump off fork
    6) apply gauge to fork reads 80psi

    I dont understand how step 4 gets you 100psi, as has been said when you attach the pump it need to be pressurised by the fork, this is the step where many think they ‘lose air’. So it should be showing 80psi when you attach, hence why i thought your pump was reading 20 above your guage. Im not doubting you, i just dont understand how.

    unfortunately its not 20 every time, varies from 10-30.
    It does seem to be to do with how fast I unscrew, but its still not a good system, no matter how fast I do it I still lose a lot of air.

    I think you might be best looking at a marzocchi pump, might be worth looking at a lower pressure pump rather than a 300psi shock pump as they can be less accurate outside the nominal working range.

    Possibly change the o-ring in the current pump first.

    Premier Icon mikewsmith
    Subscriber

    If its doing all that (the explanation as to how the pump disconnects above is a good one too) replace the valve core, done it a couple of times when they got sticky with one from an old inner tube.

    carlosg
    Member

    I have a Magura shock pump that has a little flip lever that you use to depress the valve core after you’ve screwed the shock pump on then lift again before removal . I had one of those topeak adapters but didn’t’ get on with it, no problems with my Magura pump at all.

Viewing 37 posts - 1 through 37 (of 37 total)

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