Exam Question
With reference to a rotary vane steering gear
(a) State, what symptoms would indicate leakage across vane seals (8)
(b) State what steering gear tests you would carry out before a voyage begins (8)
Class 4 (4th Engineer)
MEP
📅 Aug 2022
Reference Answer
### (a) Symptoms of Leakage Across Vane Seals in a Rotary Vane Steering Gear
Leakage across the vane seals (both fixed housing seals and moving vane seals) signifies internal bypassing of hydraulic oil from the high-pressure chambers to the low-pressure chambers within the actuator. This is a critical defect that compromises steering effectiveness. The following symptoms would indicate such a failure:
1. **Rudder Creep or Drift**: With the helm set to a specific angle (e.g., amidships) and the hydraulic pumps stopped, the rudder will not maintain its position. External forces from the sea and propeller wash will cause the rudder to slowly move, as oil leaks internally from the chamber holding the rudder against the force to the opposing chamber. This necessitates frequent corrections by the autopilot, leading to increased 'hunting'.
2. **Increased Running Time of Hydraulic Pumps**: To compensate for the internal leakage and maintain the ordered rudder angle, the control system will frequently start the hydraulic pumps to replenish the pressure in the high-pressure side. This leads to an abnormally high duty cycle for the pumps, causing increased power consumption, heat generation, and accelerated wear of the pump and motor components.
Leakage across the vane seals (both fixed housing seals and moving vane seals) signifies internal bypassing of hydraulic oil from the high-pressure chambers to the low-pressure chambers within the actuator. This is a critical defect that compromises steering effectiveness. The following symptoms would indicate such a failure:
1. **Rudder Creep or Drift**: With the helm set to a specific angle (e.g., amidships) and the hydraulic pumps stopped, the rudder will not maintain its position. External forces from the sea and propeller wash will cause the rudder to slowly move, as oil leaks internally from the chamber holding the rudder against the force to the opposing chamber. This necessitates frequent corrections by the autopilot, leading to increased 'hunting'.
2. **Increased Running Time of Hydraulic Pumps**: To compensate for the internal leakage and maintain the ordered rudder angle, the control system will frequently start the hydraulic pumps to replenish the pressure in the high-pressure side. This leads to an abnormally high duty cycle for the pumps, causing increased power consumption, heat generation, and accelerated wear of the pump and motor components.
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