Troubleshooter
Closed circuit
In a hydraulic system closed circuit the pump take oil directly from return line.
Pumps have high and low pressure sides and these change depending on the direction of load.
As a result of the expansion of pipes under pressure and internal leakage from the pumps and motors need to be added certain other components in the circuit. A feed or booster pumps which suction oil from a common reservoir and supplies to the close circuit.
A feed pump was introduce in the hydraulic system. This pump controls the main pump and fed the circuit with oil and make up for the leakage.
The components comprise the closed circuit shown are:
- Variable displacement pump (1) rotates in one direction. The pump swivel angle may be smoothly adjusted through zero, direction of flow may be changed.
- Variable displacement motor (2) rotates in both directions, may swivel one side of centre and is also adjustable.
- System flow (3)
- Pressure relief valve (4) for protection against overload
- Drain case line (5) To protect the shaft seals from being over pressurized variable displacement motors are normally drained externally.
- Tank (6) the flow which is not required is returned by feed or boost pump via boost pressure relief valve to the tank.
- Auxiliary pump vacuum (8) fluid from a common tank and fed to the closed circuit via check valve to the low pressure side of the circuit. The excess flow (fluid) is return to tank by pressure relief valve.
- Components – filter and cooler – (9) complete the hydraulic closed circuit
- Feed or boost pressure relief valve (10)
- Check valves (11) serve to separate the high pressure side from low pressure side and enable refill of the oil fed into the close circuit, irrespective of which side is under high pressure.
