problem with joe blow

moggy12

i recently bought a secondhand joeblow pro floor stand pump with the smarthead connector the problem is when i put connector on my presta valve and start pumping pressure guage goes up but as soon as i stop pumping pressure guage starts going back down and eventualy to 0 i thought once i had started pumping guage should read what actual pressure is and stay there this way i can't get a aqurate pressure reading i also tryed on my shrader car tyres and it does the same any ideas what is causing this ? will i need to replace a part ?

CrookedCucumber

Check that the head is making a proper seal over the valve. If there is already pressure in the tyre, the gauge on the pump should jump up as soon as a good seal is established. I find that I sometimes have to press the head on really hard to get a good seal.

Some of the Joe Blow pumps have some sort of air outlet right down at the bottom on the other side of the stem from the gauge. It's covered with a screw-on cap. I don't know what this outlet is for, to be honest, but the cap can work lose, and then the gauge won't read properly. So if your pump has one, check the cover is screwed down good and tight.

Of course, if you bought it second-hand, it's possible that it's simply broken

Alibran

I've had a similar problem with my pump, and I know in my case it's down to the head not opening the valve properly, so the air I think I'm pumping into the tyre is just getting trapped in a small gap between the head and the valve, then slowly leaking out again. I know my pump isn't faulty, and it's down to the original inner tubes that came with my bike having dodgy valves. I've already changed one of them, and it's fine on the new one.

If you're having the same trouble on schrader valves, it sounds like you've got a problem with the pump. It could be just a bit fiddly, or it could be broken.