Pumps, Compressors and Fluid Power Systems
Pumps
Centrifugal pumps deliver flow that falls as head rises, and each has a best efficiency point worth running near. Positive displacement pumps move a fixed volume per revolution and must never be dead-headed - they need a relief path. Cavitation shows as noise, vibration and falling flow and is prevented by keeping available NPSH above required NPSH: cool liquid, short suction line, no air leaks, suction valve open.
Compressors
Reciprocating, rotary screw and centrifugal machines differ in duty and control; all need a correctly set safety valve, inlet unloading, cooling and condensate removal. Intercoolers improve efficiency; blocked coolers raise discharge temperature and shorten lubricant life.
Fluid power
Pressure is set by the load, not by the pump. Flow sets actuator speed. Force equals pressure times effective area, and relief valves, filters, accumulators and correctly rated hoses protect the circuit. Contamination causes most hydraulic faults, so cleanliness at every opening matters.
Worked example
A cylinder with a 100 mm bore sees 10 MPa. Area = π/4 × 0.100² = 0.00785 m². Force = 10 000 000 Pa × 0.00785 m² ≈ 78.5 kN. On the rod side, subtract the rod area first - forgetting that is a common trap.
Traps
Throttling a positive displacement pump's discharge to control flow; diagnosing cavitation as a worn impeller; using pump pressure rating as the circuit's working pressure; ignoring rod area when calculating retraction force.