Originally Posted by
Good Morning
Tried the pump again on an empty tube, when i pump the presta valve, some air leaks out of the shrader valve. the tube still fills with air though, but i can't imagine getting a high psi or volume if some air keeps coming out during pumping.
The pump employs a slide valve that rides the air flow to the open port and closes it. Sometimes it can be sticky, and it's less effective at lower pressures. But once there's some resistance form the tube, the increased pressure closes the slide valve completely
If yours isn't working right, either it's a bit sticky and needs to be worked a bit, or you simply don't have enough back pressure to close it completely. You might test the valve by trying to pump against a screw or other plug of the PV port.