Uniflow scavenging

Uniflow scavenging clears exhaust from a two-stroke cylinder by admitting fresh charge air through ports low in the liner and venting through a single exhaust valve in the cylinder head, so the gas flows one way up the bore. It scavenges more completely than loop or cross scavenging, which improves charging and efficiency, and it suits the long-stroke, slow-speed crosshead engines that dominate deep-sea propulsion. The exhaust valve is hydraulically actuated and air-spring closed.