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Track pump pressure...

  • 18-09-2013 10:20PM
    #1
    Statler
    Registered Users, Registered Users 2 Posts: 894 ✭✭✭


    Think I remember a thread about something similar before but can't find it, if anyone remembers it would appreciate a link. Anyway, using a Joe Blow turbo trackpump with smart head attachment, it opens the presta valve when you flip the lever on attaching the pump head, unlike the non smart head version which only seems to open the valve when you push down on the pump. Anyway, this means, I assume, that the pressure in the tyre and pump hose are the same, as the valve is open while the pump is attached, when I take the pump head off, there's the usual blast of air coming out of the hose, but there seems to be some air loss from the tube as well, when I reattach the pump head it seems to have dropped by 5-10psi. What I would up doing was overinflating by 5psi, but having thought about it I've gone a bit OCD on it and want to make sure I have the pressure right. Anyone have a similar problem or am I just over analysing it?


Comments

  • #2
    Cee-Jay-Cee
    Registered Users, Registered Users 2 Posts: 12,235 ✭✭✭✭Cee-Jay-Cee


    I think your over analysing it. The recommended pressure for my tyres is 90-120. I pump them to 110psi, if they lose abut, so what, they're still inflated to 100+


  • #3
    jinkypolly
    Registered Users, Registered Users 2 Posts: 514 ✭✭✭jinkypolly


    Isn't it a case of when you reattach the pump the air in the tube is now filling the pump hose and therefore the readable pressure is dropping. And yes you're over analysing it.


  • #4
    07Lapierre
    Registered Users, Registered Users 2 Posts: 8,385 ✭✭✭07Lapierre


    Yes definitly OCD...and to add to it...are you sure the pump gauge is accurate? :)


  • #5
    Idleater
    Registered Users, Registered Users 2 Posts: 6,176 ✭✭✭Idleater


    07Lapierre wrote: »
    Yes definitly OCD...and to add to it...are you sure the pump gauge is accurate? :)

    Never mind accounting for temperature and atmospheric pressure


  • #6
    07Lapierre
    Registered Users, Registered Users 2 Posts: 8,385 ✭✭✭07Lapierre


    U should really put nitrogen in your tyres...its much more stable than boring old Air!


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  • #7
    redmaxi
    Registered Users, Registered Users 2 Posts: 297 ✭✭redmaxi


    When you attach the hose then the volume of air required to fill the hose back to the gauge will cause a reduction in pressure (Boyle's Law). But when you have pumped to the correct pressure and turn the lever, the air escaping is the volume in the hose not the tube so depending on the accuracy of the pump gauge the pressure remains correct until you re-attach the hose of course...


  • #8
    Statler
    Registered Users, Registered Users 2 Posts: 894 ✭✭✭Statler


    Air going back into the hose would explain it alright, (I really should have thought of that) and thanks for the suggestion re temperature and atmospheric pressure but I think I've put enough thought into this one and should move on!


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