My Silca floor pump has been acting up. When I stick it onto the presta valve it fits fine but when I pump the needle doesn't stay up at to where the tire pressure is but goes back down to 0. Normally after the first pump the needle points to and stays at the pounds of pressure that the tire is filled to then with each pump it rises to the desired pressure. But now it just rises during pumping and then lowers as I lift the pump handle to refill the air. I've replaced the rubber end washer AND the leather inner washer. Any ideas???

Sounds like you have a leak in the tube (flat tire).

It can't be the tubes. I tried the pump on 3 different bikes, none of them have bad tubes.