The diagram shows the telemotor/control transmitter -> duplicate hydraulic pump units (port and starboard pumps, each with its own motor and relief valve) -> the four-ram steering gear: two double-acting rams in each actuator, i.e. four cylinders/rams (two cylinders of two rams, or two double-acting cylinders). Each cylinder is connected via the pipe line to the pump delivery on both sides of the ram. The valve arrangement comprises:

• Relief valves (s) on the pump delivery/high-pressure side that open at a set pressure to protect the system (e.g. above the working pressure) and by-pass excess oil back to suction/tank.
• Make-up (charging) valves: pilot/charging valves that admit oil from an expansion/charging tank to maintain the circuit full of oil and make up any leakage.
• Isolating valves: gate valves at each cylinder/ram so that a cylinder (e.g. a fractured one) can be shut off (bypassed) without losing the whole steering gear.
• By-pass valves: a by-pass (short-circuit) arrangement so that when one cylinder is isolated its rams are connected to allow oil flow/return (the disabled ram is bypassed and its oil flows freely) so it does not lock or resist.

A single-line diagram shows: charging/make-up tank -> make-up valves -> pump (duplicate) -> relief valve -> isolating valves -> cylinder A and cylinder B -> bypass valve linking the two sides of each disabled cylinder. Telemotor control operates the pumps.

If one cylinder/ram is fractured (e.g. the cylinder casing has developed a crack/leak), the corresponding isolating valves are closed to cut off that cylinder from the main system, and the by-pass valve on that cylinder (or the isolating/by-pass arrangement) is opened so that the ram can still move freely and oil displaced by it returns through the by-pass instead of building up pressure in the broken cylinder. This removes the damaged cylinder from service while the remaining rams continue to operate the rudder (with reduced torque). The relieving valve and make-up valves maintain the pressure/level. The vessel then continues steering on the reduced capacity until repairs are made, with due care of rudder loads.

A low-level alarm is provided by a sight glass/level switch in the charging/expansion tank (the make-up tank). If oil leaks from the system, the level in the charging tank falls; a level switch/float activates an alarm (lamp and audible alarm, and a low-level indication at the steering gear and at the bridge). Additionally, a pressure switch on the circuit may raise an alarm if the oil pressure falls, and the relief/by-pass flows would normally restore but the loss of oil shows as falling level in the make-up tank. This gives immediate warning of leakage so that the crew can isolate the leaking circuit.