Floor Pump Problem - Air Loss after Pumping

[C.H. Luu]

Hi Guys:

My Topeak Joe Blow Sport pump took a dive on me after many years of
use. Instead of buying a new hose with fitting, I decided to buy a
new pump. I purchased a Topeak Joe Blow Pro with a flip lock switch
nozzle that is able to accomodate Shraeder & Presta valves with the
same nozzle.

Although it pumps very easily, I have noticed a very "annoying" side
effect. I pump my tires to 120psi and after unlock the head via the
flip lock switch, I remove the nozzle from my presta valve. I notice
that there is a loud hissing noise. At first I thought it was from
air inside the hose but after checking the pressure in my tires, I
find that the tire has lost 5-10 psi. Is there a way of preventing
this? I tried a Blackburn Air Tower 5 with a similar type of inflator
head and it has the same problem.

Any help is appreciated.

Thanks,
Claude

 

[[email protected]]

On Tue, 03 Jul 2007 04:54:10 -0000, "C.H. Luu" <[email protected]>
wrote:

>Hi Guys:
>
>My Topeak Joe Blow Sport pump took a dive on me after many years of
>use. Instead of buying a new hose with fitting, I decided to buy a
>new pump. I purchased a Topeak Joe Blow Pro with a flip lock switch
>nozzle that is able to accomodate Shraeder & Presta valves with the
>same nozzle.
>
>Although it pumps very easily, I have noticed a very "annoying" side
>effect. I pump my tires to 120psi and after unlock the head via the
>flip lock switch, I remove the nozzle from my presta valve. I notice
>that there is a loud hissing noise. At first I thought it was from
>air inside the hose but after checking the pressure in my tires, I
>find that the tire has lost 5-10 psi. Is there a way of preventing
>this? I tried a Blackburn Air Tower 5 with a similar type of inflator
>head and it has the same problem.
>
>Any help is appreciated.
>
>Thanks,
>Claude

Dear Claude,

At any significant tire pressure, a presta valve should close almost
instantly when the outside pressure drops.

If 120 pis pressure really does drop 5-10 psi when the pump head comes
off quickly and normally, then you have a defective presta valve.

But the dedicated gauge that you're using to measure the pressure
afterward may simply be reading low and thus disagreeing with the
inline gauges of your two air pumps.

If that's the case, the vote is two to one in favor of the higher
pressure. That is, you may be seeing this situation at a true 120 psi:

Topeak inline gauge: 120 psi
Blackburn inline gauge : 120 psi
unknown tire gauge: 110-115 psi

Of course, the dedicated gauge could be right, and your two inline
gauges could be reading 5-10 psi.

Another possibility is that you are mis-reading the inline gauges,
whose markings are not always as clear as dedicated gauges.

With a floor gauge, you can reattach the hose, pump up the dial
slowly, tapping the valve with a handy screwdriver, and note when the
presta valve breaks loose--if it settles at the same setting, then you
aren't losing 5-10 psi.

Cheers,

Carl Fogel

 

[Michael Warner]

On Tue, 03 Jul 2007 04:54:10 -0000, C.H. Luu wrote:

> At first I thought it was from
> air inside the hose but after checking the pressure in my tires, I
> find that the tire has lost 5-10 psi. Is there a way of preventing
> this? I tried a Blackburn Air Tower 5 with a similar type of inflator
> head and it has the same problem.

Unless the valve is defective and not closing quickly when the hose
is removed, it's merely a difference in the readings between the pump
gauges and whatever else you're using afterwards. Cheap gauges
aren't very accurate.

--
Home page: http://members.westnet.com.au/mvw

 

[Steve Gravrock]

On 2007-07-03, [email protected] <[email protected]> wrote:
> On Tue, 03 Jul 2007 04:54:10 -0000, "C.H. Luu" <[email protected]>

[ air loss when removing pump head from valve ]

> At any significant tire pressure, a presta valve should close almost
> instantly when the outside pressure drops.
>
> If 120 pis pressure really does drop 5-10 psi when the pump head comes
> off quickly and normally, then you have a defective presta valve.

I have the same problem with my floor pump as Claude does with with his,
and at least in my case the pump head seems to be at fault. The problem
is that some pump heads open the valve when pushed on but don't seal
around it until the lever is flipped up. I have a Bontrager floor pump
that works that way. Air escapes from when I push the head onto the
valve until I flip the lever up and again from when I flip it down until
I pull the head off the valve. Pumping to 90 PSI, removing the pump
head, and putting it back on consistently gives me 80 PSI. On the other
hand, my Road Morph and my friend's Specialized floor pump both seem to
use the lever only to hold the head on the valve. I don't lose any
pressure with those pumps.

I also have a shock pump with the same problem. It uses a thread-on
Schraeder valve. The faster you unscrew it, the less pressure you lose.

 

[C.H. Luu]

Hi Carl:

Thanks for the advice. Reinstalling the head of the same pump onto
the presta valve, consistently reveals a pressure drop. I might just
go back to my Joe Blow Sport with the Twin Head nozzle. However,
pumping a little more to compensate for the drop isn't too drastic of
a cure.

Many thanks for your insight.

Claude

 

[[email protected]]

On Thu, 05 Jul 2007 02:11:03 -0000, "C.H. Luu" <[email protected]>
wrote:

>Hi Carl:
>
>Thanks for the advice. Reinstalling the head of the same pump onto
>the presta valve, consistently reveals a pressure drop. I might just
>go back to my Joe Blow Sport with the Twin Head nozzle. However,
>pumping a little more to compensate for the drop isn't too drastic of
>a cure.
>
>Many thanks for your insight.
>
>Claude

Dear Claude,

Whatever's causing the problem, it ain't right, butit's hard to see
anything wrong f you can pump to 125 psi, drop to 120 psi, and are
happy with the adjustment.

Something must be pushing the presta valve down and holding it open
after the head is pulled off enough that the seal opens.

You may have a bent or badly manufactured presta valve that somehow
shuts slowly and grudgingly. Or your pump heads could be poorly
designed (or even defective).

If you're curious, you could borrow a few pumps and test your tubes,
or try your pump on a few other tires.

My cheap yellow floor pump with a dual head seems to work well on
700x26 at 120 psi. In fact, I use it as a gauge to save time--put the
pump head on, pump up until the valve breaks, and replace the tube if
it's lost more pressure than seems right. Usually I find a slow leak
from a goathead thorn, partly sealed by slime.

Cheers,

Carl Fogel

 

[Dennis Ferguson]

On 2007-07-05, [email protected] <[email protected]> wrote:
> On Thu, 05 Jul 2007 02:11:03 -0000, "C.H. Luu" <[email protected]>
> wrote:
>>Thanks for the advice. Reinstalling the head of the same pump onto
>>the presta valve, consistently reveals a pressure drop. I might just
>>go back to my Joe Blow Sport with the Twin Head nozzle. However,
>>pumping a little more to compensate for the drop isn't too drastic of
>>a cure.
[...]
> Whatever's causing the problem, it ain't right, butit's hard to see
> anything wrong f you can pump to 125 psi, drop to 120 psi, and are
> happy with the adjustment.
>
> Something must be pushing the presta valve down and holding it open
> after the head is pulled off enough that the seal opens.

The pump he has is this one (I have one too):

http://www.topeak.com/2007/products/floorpumps/jbpro.php

The pump's head doesn't have dual holes, one for each valve type, it
instead has one single hole which accomodates both Schrader and Presta
valves without any adjustment. Inside the head is the pin needed to
open Schrader valves. This pin moves into and out of the head fairly
freely when the locking lever on the head is open (it is pushed out
by a very light spring), but is pushed all the way out into the valve
when the locking lever is closed.

The problem with the pump when used on Presta valves seems to be that
when you've finished inflating the tire and have openned the locking
lever, for the Presta valve to close, the valve must push the pump head's
pin back into the pump head against the force of the pin's spring. This
seems to slow the closure of the valve enough (with the valves on the
tubes I use, at least) that the tire loses a few psi before the valve
manages to entirely close.

I've done alright with the pump for 2 or 3 years now by the same method,
inflating the tire 5 or so psi higher than I actually want it to end up.
I wouldn't mind if something happened to the pump which gave me an excuse
to buy something else, however.

Dennis Ferguson