What is this lump in the picture and how does it work?

enter image description here

I have another pump, which physically is the same but minus the bulge. The one in the picture seems to perform better, ie less work to reach the same pressure.

  • 5
    It would appear to be a pressure reservoir, so that when you push down on the pump and all that air can't immediately flow through the narrow hose and into the tube, some of it is stored in the reservoir to be released more slowly. This would make it easier to pump up a tire, since if the air wasn't stored it would just increase the pressure pressing back on the pump handle. May 22, 2015 at 11:36
  • How does it work?
    – Old Geezer
    May 24, 2015 at 0:41
  • 1
    It's fairly passive. It just a holding tank that absorbs the excess air when you press down hard and fast, then releases it more slowly. May 24, 2015 at 0:59

1 Answer 1


This from an old article circa 1996 it references a Medai floor pump. "Screwed into the base near the compression tube is an air tight steel chamber. This chamber is known as a reservoir and holds a volume of the compressed air to assist in equalizing the pressure of the pumps compression chamber and the inner tube. This feature gives the tire a small assist in time as it "seats" on the rim."

  • How does it work?
    – Old Geezer
    May 24, 2015 at 0:41

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.