working and pumping pistons forming stepped piston

Full Title

Engines characterised by provision of pumps for charging or scavenging > Engines with reciprocating-piston pumps; Engines with crankcase pumps > with reciprocating-piston pumps other than simple crankcase pumps > with the pumping cylinder situated between working cylinder and crankcase, or with the pumping cylinder surrounding working cylinder > working and pumping pistons forming stepped piston