Hydraulic Systems A centralised hydraulic system sy stem consists of:
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Duplicated
oil pumps and motor
Accumulator Filters Oil
reservoir ( oil tank)
Control
valves
Pipework Pressure
regulators
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Hydraulic system components Hydraulic valves & indicator Hydraulic valves group
-close up.
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Hydraulic system components Hydraulic pumps
Electric motor drive
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Hydraulic system components Hydraulic oil tank
Hydraulic pumps
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Hydraulic Systems Open Loop System The system takes oil from the tank and pumps it into the hydraulic motor. A control valve is positioned in parallel with the motor. When it is open, the motor is stationary; when it is throttled or closed the motor will operate. The exhaust oil returns to the tank Commonly used in low pressure system and are simple in design as well as reliable. •
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Open Loop System
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Hydraulic pump
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Closed Loop System In the system, the exhaust (low pressure) oil is returned direct to the pump suction. •
Since the oil does not enter an open tank, the system is considered closed. •
Suitable for medium pressure system in marine application . •
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Closed Loop Systems
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Centralised Hydraulic Power System
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Hydraulic Systems
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Hydraulic Systems Spool Valve Pilot operated four port directional valve.
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Valve is available with either two or three operating positions with choice of spring offset, spring centered, detent control or free spool •
Flows depending on valve size.
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Maximum pressure 210 bars.
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Hydraulic Systems - Spool Valve
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Hydraulic Systems Accumulators To maintain circuit pressure by compensating for pressure loss due to leakage or temperature rise. To supplement pump delivery where multiple circuit operation have wide flow variations. To absorb shock by cushioning circuit pressure rise as a result of sudden valve closure. To provide a high energy power source where there is high energy discharge after relatively long charging period. •
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Accumulator
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Hydraulic System Hydraulic oil Properties Low pour point ( -50 degree centigrade)
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Low viscosity ( 30 sec Redwood I at 600 C)
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High flash point ( closed flash point 1500 C)
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Non corrosive
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Non sludge forming
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Factors affecting Hydraulic System Operation Temperature
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Cleanliness
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Hydraulically Operated Hatch Cover Two hydraulic rams actuated by an external power source and controlled locally on side of hatch coaming The rams are used to turn one pair of hatch covers, at their hinges, through 180 degrees. Each pair of hatch covers are linked together by hinges When the covers are opened by rolling back, they are moved into the vertical position automatically. •
