My pump got little rusty from rain. So i tried gear oil on it. But now its not pumping, just sliping all the way down. Is it because of oil or the valve is damaged? I tried removing the oil with detergent. But its not working.

  • Generally it's a bad idea to use conventional petroleum products around rubber pieces such as the piston seal and chuck valve. It sounds like the piston seal is the problem, so you need to disassemble the pump and thoroughly clean the seal at the end of the piston and the interior of the cylinder with detergent. Probably the best readily-available lubricant is automotive brake fluid. – Daniel R Hicks Mar 30 '19 at 18:52
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    Note that if the problem were that you pressed down and the air went into the tire, but as soon as you stopped pressing the air came back out, that would be a problem with the valve in the chuck. But if the pump presses all the way down with little resistance the problem is with the seal (and possibly a small valve) on the end of the piston. – Daniel R Hicks Mar 30 '19 at 18:54
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    @DanielRHicks is there a valve in a bicycle pump? I have not used a pump where the air from the tyre would not push the piston back when the pump is not correctly connected and the inner tube's valve cannot close. (Doesn't mean there is no such thing, hence the question.) – gschenk Mar 30 '19 at 21:07
  • @gschenk - Depends on the pump (and the tire valve). Some pumps depend on the tire valve as a "check" valve, while others (especially your more "general purpose" pumps) incorporate their own check valve, either in the chuck or in the fitting at the bottom of the pump. A lot of Schrader pumps, in particular, have a pin in the chuck which holds the tire valve's pin depressed while the chuck is installed. – Daniel R Hicks Mar 30 '19 at 21:19
  • What happens if you just block the chuck with a finger? Is there build-up of pressure? Check the piston. If it has been disassembled check for correct re-assembling (damaged seal?). – Carel Apr 3 '19 at 14:59

I have found that cleaning the internals, and light lubrication with a light silicon grease works wonders. Silicon won't hurt the rubber

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