Compact manual air pump having selectable high volume and high pressure modes

摘要

A pump comprises a pair of coaxial pistons, one slidably positioned in the other for simultaneous compression causing oppositely directed air flow, a passage having a valve for permitting air flow from one such piston to enter the other such piston for increased air flow, and a switching device for selectively opening the passage to ambient for preventing air flow between the pistons. The pump thus has two modes, namely, a high volume mode when the two pistons operate simultaneously to direct combined air flow and a high pressure mode when the passage is opened to ambient to direct air flow from only one of the two pistons having a smaller bore.