Bicycle Mechanics - 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?

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.

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.

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.

I beleive that you guys are talking about schrader valves. If I understand the problem correctly the extenders are for presta valves.

I was talking about presta.