Abstract: In an aspirator (10) for pumping air into an inflatable (16), initial delivery of an aspirating fluid extends a piston (68) and the piston (68) extends an aspirator tube (24) to open an ambient air inlet (30) and render the aspirator (10) operable. Aspirating fluid pressure acts on a valve plug (112) and moves it into a first position in which the aspirating fluid pressure is connected to the linear fluid motor (66) for extending the piston (68). When inflation is substantially completed, back pressure from the inflatable (16) acts on a movable wall (74) which is connected to the valve plug (112) to produce a force which overrides the force of the aspirating fluid pressure acting on the valve plug (112). The overriding force moves the valve plug (112) into a second position in which flow of aspirating fluid into the linear motor (66) is blocked and the piston (68) is vented. A spring (48) then retracts the aspirator tube (24 ) closing the ambient air inlet (30), and disabling the aspirator (10).