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Exhaust valve control

Sulzer RT-flex. Exhaust valve control

The exhaust valves are operated by a hydraulic “push rod”, being opened by hydraulic oil pressure and closed by an air spring, as in the Sulzer RTA engines with mechanical camshafts. But for RT-flex engines the actuating energy now comes from the servo oil rail. There is one exhaust valve actuator (also known as the partition device) for each cylinder.

In the exhaust valve actuator, fine-filtered servo oil acts the underside of a free-moving actuator piston, with normal system oil above the actuator piston for valve actuation. The adjacent hydraulic control slide is precisely activated by a Sulzer rail valve and controls the flow of servo oil to the actuator piston so that the exhaust valve opens and closes at precisely the correct time with appropriate damping. The exhaust valve actuator employs the same Sulzer rail valves as are used for the ICU.

Fig 8. The exhaust valve actuator with the large-diameter actuator piston on the left and the hydraulic control slide in the right
The exhaust valve drive on top of the valve spindle is equipped with two analogue position sensors to provide a feedback on valve operation to the WECS.
The electronically-controlled actuating unit for each cylinder gives full flexibility for exhaust valve opening and closing patterns. At the same time, the actuating unit provides a clear separation of the clean servo oil and the normal system oil. Thus the exhaust valve hydraulics can be serviced without disturbing the clean servo oil circuit.

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