My new 29er came with Presta valves instead of the old school schrader valves that were on all my older bikes. I understand that they hold air better, but I'm having a hard time getting them filled up with either my bike pump, or my air compressor. I have the small aluminum converter that screws into the pump, but there always seems to be air escaping on both tires, no matter how hard I push it down. So, I can't get an accurate gauge on my tire pressure, and it's driving me crazy. I know this seems like a stupid question, but is there a trick to these valves? I simply unscrew the valve stem, press down my gauge to pump air, and close the valve to clamp onto the valve stem. Am I missing something?