Hydraulic Systems: Components and Indications
The basic circuit
A hydraulic system needs a reservoir, a pump, a pressure regulator or relief valve, an accumulator, filters, selector valves, actuators and a return path. Know the difference between an open-centre and a closed-centre system, and which one suits a system with continuous pump output. Understand that the relief valve protects the system from overpressure while the pressure regulator controls pump output.
Accumulators and pumps
An accumulator stores hydraulic energy in a compressed gas or spring and damps pressure pulses. Traps include the precharge question: precharge is set with no hydraulic pressure on the fluid side, and a low precharge gives poor pressure holding and possible pump cycling. Know engine-driven pumps, electric pumps and hand pumps, and why a check valve prevents backflow through a failed pump.
Actuators and valves
Be able to distinguish single-acting from double-acting actuators, and explain the role of a shuttle valve, sequence valve and priority valve. A selector valve directs flow; a check valve permits one-way flow; a flow-control valve limits rate. Traps include confusing a sequence valve (operates in a set order) with a priority valve (gives one consumer flow first).
Indications and worked example
System indications typically show pressure, quantity and sometimes temperature. Worked example: if a system shows normal pressure but slow actuator movement, suspect a flow restriction or a failing pump delivery rather than low pressure, because the accumulator can hold pressure while flow is inadequate. Rule of thumb: pressure tells you the system is charged; flow tells you it can do work.