(under the class definition) Apparatus comprising two or more pump chambers there being provided means for separately controlling the inlet of fluid to each chamber and each chamber being provided with a relatively movable wall portion (e.g., piston) for changing the chamber volume; there being
additionally provided a flow path for establishing intercommunication between said chambers which is distinct from the normal pump fluid inlet flow paths, said flow path being controlled as a result of the wall portion reaching a predetermined position in one of said pumping chambers.
(1) Note. For purposes of this definition, the plural pumping chambers may be formed by a single cylinder having a single piston therein providing oppositely facing pumping faces for dividing the cylinder into plural chambers.
