It's frustrating getting a flat tire on your bike and finding your bike pump doesn't work. Of course the worst time to discover the problem is out on the road, miles from help. Check to be sure your pump works correctly before you venture out. Problems with bike pumps include incorrect valve type, a stuck check valve, and worn or dirty seals.
Valve Problems
Bicycle inner tubes come with two valve stem types: Presta and Schrader. Your bike pump must fit the tube type. Presta valves are smaller, lighter and supposedly seal better, but require an adapter to fit most pumps. Schrader valves are the most common type of valve stem, and the vast majority of bike pumps will fit without issue. Problems with the valve stem seal are common. Keep dirt out of the valve stem fitting by wiping the valve stem clean before pumping. Press the pump's air fitting firmly down over the valve stem and flip the lock lever closed. This creates a tight rubber seal around the stem and opens the valve inside the valve stem of the inner tube. Some pumps are adjustable so you may have to experiment with the valve attachment to get it to seat properly. Air escaping means you have a poor seal.
Internal Pump Problems
Inside your bike pump is a check valve that allows air to flow in only one direction. If corroded or dirty, this valve can be stuck into position. If the valve is stuck open, any air you pump into the tire will simply rush back out. The valve can also stick in the closed position, in which case you will feel a great deal of resistance but air will not inflate the tire.
Air Seal Problem
Problems arise when dirt is in the orifice of the valve or on the valve stem. Your bike pump has to form a tight seal around the valve so that the air you pump goes into the tire instead of the atmosphere. Dirt or wear in the seal area will leave you pumping until you wear out and leave your tire flat. A less common problem is the seals inside the pump. If these are worn out, air escapes past the seals instead of flowing through the valve and into your tire. You will notice less resistance while you are pumping and the tire inflating very slowly.
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