Hydraulically Operated

Hydraulically actuated marine check valves are used in piping systems where reverse-flow prevention must be combined with a controlled hydraulic response. Unlike basic swing or lift check valves, their operation relies on line pressure and an internal or auxiliary hydraulic control arrangement so that closure occurs when forward flow stops or when backpressure develops.

This category includes Cla-Val 81PM-1, 181M-EP, 181M-2, and 181PM-EP. These valve types are referenced for AFFF fire-fighting systems on surface vessels to prevent reverse flow of foam solution during system operation. The 181M-2 functions as a check valve that permits flow in one direction and closes when backpressure is established. The 181M-EP and 181PM-EP are described as being manufactured in accordance with MIL-F-20042 / MIL-F20042 requirements for AFFF service.

Valve selection should be based on the fire system operating sequence, available actuation pressure, compatibility with seawater and foam concentrate solution, required closing speed, and interface with pumps, proportioners, manifolds, and AFFF distribution lines. In critical service, the valve should be evaluated as part of the hydraulic control logic of the network rather than as a standalone non-return component.

Maintenance should include inspection of the seat, diaphragm or hydraulic control element, internal passages, elastomers, and fluid cleanliness. Foam residue, salt deposits, or suspended solids can affect shutoff tightness and response time, particularly in systems that remain on standby for extended periods.