Vacuum line control valves

A vacuum line control valve having a single vacuum input port and a pair of output ports to which vacuum is supplied alternately, each output port being vented to atmosphere when not at vacuum pressure. A reciprocating valve control member is carried by a resilient diaphragm which separates two internal chambers. A first valve control setting corresponds to the initial, rest position of the diaphragm. Differential pressures in the chambers first displace the diaphragm to the second valve control setting and then return it to the first. Frequency of alternation is determined by a bleed aperture between one output port and one chamber.