Cycling and bicycle discussion forums. 
   Click here to join our community Log in to access your Control Panel  


Go Back   > >

Bicycle Mechanics Broken bottom bracket? Tacoed wheel? If you're having problems with your bicycle, or just need help fixing a flat, drop in here for the latest on bicycle mechanics & bicycle maintenance.

User Tag List

Reply
 
Thread Tools Search this Thread
Old 05-15-08, 07:11 AM   #1
king-tony
Ninja don't wear flipflop
Thread Starter
 
king-tony's Avatar
 
Join Date: Aug 2007
Location: NE TN
Bikes: Specialized S-Works Roubaix SL3, BMC TM01...if it every ships
Posts: 1,443
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
valve extenders and pressure readings

I have a friend who just switched to tubulars and is using valve extenders. I believe that they are properly installed and when he uses his silica pump to inflate the tires, they do inflate, however the pressure gauge on the pump only moves while air is being pumped in (in other words on the down stroke of the pump the gauge will move to about 20psi and then fall back to zero). Any idea what would cause this?
king-tony is offline   Reply With Quote
Old 05-15-08, 07:19 AM   #2
kycycler
Senior Member
 
Join Date: Mar 2007
Location: Louisville, KY
Bikes: Trek Madone 5.5, Klein Q Pro Elite, Surley LHT
Posts: 469
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
most likely a leak in the extender, There is a o ring inside the extender for the seal. check to see if the extender is securely tightened to the valve stem.
kycycler is offline   Reply With Quote
Old 05-15-08, 07:32 AM   #3
pmseattle
Senior Member
 
pmseattle's Avatar
 
Join Date: Jun 2004
Location: Seattle, WA
Bikes:
Posts: 451
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Quote:
Originally Posted by king-tony View Post
I have a friend who just switched to tubulars and is using valve extenders. I believe that they are properly installed and when he uses his silica pump to inflate the tires, they do inflate, however the pressure gauge on the pump only moves while air is being pumped in (in other words on the down stroke of the pump the gauge will move to about 20psi and then fall back to zero). Any idea what would cause this?

With the valve extender on, the valve does not open until you start pumping since the inside of the pump head is not making contact with the valve stem and pushing it open. As you pump, the pressure inside the pump will force the valve stem to open.
pmseattle is offline   Reply With Quote
Old 05-15-08, 08:13 AM   #4
masiman
Senior Member
 
Join Date: Oct 2005
Bikes:
Posts: 1,735
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Quote:
Originally Posted by pmseattle View Post
With the valve extender on, the valve does not open until you start pumping since the inside of the pump head is not making contact with the valve stem and pushing it open. As you pump, the pressure inside the pump will force the valve stem to open.
I don't know about you but I don't push my pump head onto the valve enough press the valve open. In the end, it does not matter whether the pump head pushes the valve open or not. It only matters that you can build enough pressure between the pump check valve and the tire to inflate it. Any leaks in the system make inflation less efficient to impossible. With a leak in the extender, each pump will have to rebuild pressure in the hose and surpass the tube pressure to fill it. Meanwhile, the pressure is being lost by the leak in the valve extender, causing you to have to rebuild that lost pressure with the next pump. Eventually you'll reach equilibrium and will not be able to pump in any more air without changing the system.
masiman is offline   Reply With Quote
Old 05-15-08, 02:08 PM   #5
kycycler
Senior Member
 
Join Date: Mar 2007
Location: Louisville, KY
Bikes: Trek Madone 5.5, Klein Q Pro Elite, Surley LHT
Posts: 469
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
I beleive that you guys are talking about schrader valves. If I understand the problem correctly the extenders are for presta valves.
kycycler is offline   Reply With Quote
Old 05-15-08, 02:20 PM   #6
masiman
Senior Member
 
Join Date: Oct 2005
Bikes:
Posts: 1,735
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
I was talking about presta.
masiman is offline   Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off



All times are GMT -6. The time now is 12:53 PM.