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I got a Diamondback Viper for Christmas. The tires got a bit deflated so I got a $5 bike pump and I attempted to pump up the tires. All went well for a couple of seconds then all the air from the tube went back out the pump. I'm not sure if its the pump or the valve. It's a Schrader valve.

I'm not sure what to try to fix the issue. I have tried pumping it up multiple times all the same result. I know it's normal to lose a bit of air when getting the pump off but I'm not sure about this.

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I know it's normal to lose a bit of air when getting the pump off but I'm not sure about this

The air you lose when taking the pump off should be just a very brief hiss. And, actually, it's mostly air coming out of the pump, not out of the tyre. You shouldn't lose any significant amount of pressure when taking the pump off. The only thing I can think of to do wrong when taking off the pump is if you have the type where a tube screws into the pump and onto the valve. You need to unscrew the valve end of the tube first, but surely that's what you'd do anyway.

Did the same thing happen to both tyres? If so, it's the pump. If one tyre inflates and the other one doesn't, it's the valve, and you need a new inner tube. I've never had a valve go bad but I guess it happens occasionally. Check if there's any grit visible, which might be holding the valve open or something.

If you want to try a different pump, go to a bike shop: they'll have one that you can use. Avoid gas station air pumps if you can: they're designed to fill the relatively huge volume of a car tyre so they dispense a lot of air very quickly and overinflate your tube before they even notice they've done anything.

A $5 pump probably isn't great but it should be fine for BMX tyres, which don't need to be inflated to high pressure.

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To find out whats wrong all parts must be tested separately. Take your bike to the nearest gasstation and try filling up your tires there. Schrader valves are the same ones that are used by cars.

If that works the problem is with the pump, if it's something wrong with the bike.

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    Be very careful with gas station air pumps. They're designed to dispense large volumes of air quickly (car tyres have enormous volume compared to bike tyres) and it's easy to over-inflate your little bike tyre before the pump even notices.
    – David Richerby
    Commented Apr 28, 2019 at 8:46
  • Seconding what David Richerby said, and adding that the issue is much more severe with wide, baloony bike tires than with thin road tires. The thin road tires can hold a lot more pressure while putting the same stress on the rim as the low pressure baloony tires do. If your gas stations pump uses a prepressure of 10bar, a thin tire rated for 6.5bar is likely to survive, as is the rim. With a thick tire rated for max 2bar, that same pump is very likely to explode either the tire or the rim.
    – cmaster - reinstate monica
    Commented Apr 28, 2019 at 10:57
  • Guess the gas station pumps differs from area to area then.. The ones I've been using have a mechanical button that you can tap or press carefully, I never had a problem doing it as long as you watch the pressure and fill up carefully
    – Bjathr
    Commented Apr 29, 2019 at 16:17

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