A pump having adjustable pumping pressures includes a tube, first and second chambers and a channel extending from the first end to the second end of the tube, and an orifice extending through the tube and opening to the channel. A base connected to the second end of the tube includes a first passage opening to the first and second chambers and a second passage opening to the first passage and the channel. A switching device includes a rod disposed in the channel and a shaft received in the orifice for selectively moving the rod to a first position for permitting air flow through the second passage to the channel and a second position for preventing air flow through the second passage to the channel.