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My bike has sat over the winter, and the tires went flat. I used my foot pump to inflate the tires (front and back) and both tires inflated to 30 psi. I have shraeder valves. The pump continued to working with the same amount of resistance, but the psi on both tires would not go above 30. I am assuming that since the tires did inflate up to 30 psi, the valve connected, air is getting into the tire, and the pin is not stuck. Maybe I am wrong. Hoping someone else has had this issue and can share the fix.

Update. There is no sound of air escaping anywhere. I left the pump connected to the valve over night, and the psi did not decrease. The Gauge on the pump goes up to 100psi.

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    It might be that the pump is working, but the gauge on it is not. Use an alternative gauge (e.g. another pump or a standalone one) to get a second opinion, or at least knock slightly the one on the pump to make sure it is not friction or a broken gauge. What sort of a pump are you using? Disclosing that might help answering the question. – Grigory Rechistov Jul 27 '20 at 7:06
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    @GrigoryRechistov In that case, you would expect the resistance of the pump to increase as the pressure in the tire rises. However, the question says: "The pump continued to working with the same amount of resistance." So, a broken gauge is not the answer. – cmaster - reinstate monica Jul 27 '20 at 7:52
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    Your main tool to debug pump problems is your ear. Listen to the sounds of air streaming into the tire, or out of the valve, and try to understand what precisely the air is doing. This can give you valuable clues what the problem could be. – cmaster - reinstate monica Jul 27 '20 at 7:55
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    It may be that some of the seals inside the pump or the chuck are dry or cracked, deformed or something alike, causing a small leak and it just happens to limit pump's capacity to 30 psi. If you have access to another pump, try and see if you can achieve higher pressure. Also try to inflate something else using your pump and see if it can go over 30 psi. (many car tires can hold mucho more than 30 psi. A test can be made and then return the pressure to normal) – Jahaziel Jul 27 '20 at 17:25
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    Here is another test you can make: Pour a little amount of soapy water over the chuck when connected to your tire and use the pump. If at some point bubbles develop then the cause is a leak so small that is inaudible. With this you can also test the pump´s hose and the connections. – Jahaziel Jul 27 '20 at 17:29
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I don't think it's likely that there's a problem with the valve or tube. You should check it with a separate pressure gauge and try a different pump.

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I'd suspect the pump seals, having had trouble before. I've had this with my Mini Morph, and ended up replacing the O-ring; regreasing is another option and the first thing to try.

Sometimes the inlet seal is OK statically but leaks dynamically when you pump. The peak pressure inside the pump is considerably higher than the pressure in the tyre, as it has to overcome the valve spring and push air down a narrow tube. You wouldn't hear the air escaping because it only does so when you're putting in effort and moving parts against each other, so masking the sound.

Sometimes it's a seal where the hose leaves the body, that might need greasing and/or tightening.

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