Marine Engineering Study Materials

Relief Valves

Relief valve to be fitted to any part of the hydraulic system, which can be isolated if required. The setting of relief valve shall not exceed the design pressure. Relief valve shall be of adequate size and so arranged as to avoid an undue rise in pressure above the design pressure. Relief valve protect piping and hydraulic system against over pressurizing.

• Relief valve setting should not be less than 1.25 times the working pressure.
• Discharge capacity of relief valve should not be less than 110% of the total capacity of pumps.
• Rise in pressure should not exceed more than 10% of the set pressure, this safeguards against the excessive torque on rudder stock in rough seas.
• Relief valve also should function in case of maladjustment of hunting gear in case rudder coming in contact with some foriegn objects or rudder movement gets restricted.
• Relief valve of the pumps cannot be substituted for the shock valves.

Steering Gear Control

• Control for main steering gear should be provided from both navigation bridge and steering compartment.
• In case of chemical tankers and gas carriers two independent hydraulic tele-motors shall be fitted.
• Auxiliary steering gear shall be operated independently from the wheel house.
• There should be two independent power supply for the control circuits, one from main switch board and one from emergency switch board.
• If no emergency generator is there, then two independent connections to be fed to the controller circuits from port and starboard side of the main switch board, so that in case of fire, one can be isolated.
• In case of failure of main steering gear, second one should start within 45 seconds.
• Audio and visual alarms to be provided in wheel house for failure of power to the steering gear and control system.
• Only short circuit protection to be provided on main supply and control system, by means of fuses.
• There should not be any overload trips, only overload alarms to be provided.
• Rudder angle indicator to be fitted in wheel house, bridge wings and steering compartment.
• Ensure dedicated communication system in place, between wheel house and wheel house.
• Gyro repeater to be fitted in steering gear room so that ship can be steered on desired course from steering room.
• On wheel house control of steering gear, it should be in position to operate under manual mode (Follow up and Non-Follow up) and auto pilot mode. Change over switch to be provided in wheel house so that in case of emergency operator can change over control to steering room if necessary.