Hydraulic cylinder circuit
A basic circuit: pump, relief valve, a 3-position directional control valve and a double-acting cylinder. Set the bore, rod, pump flow, relief setting and load, then shift the valve to extend, centre and retract. Watch the oil, the gauge and the rod, and see why the same cylinder pushes harder one way and moves faster the other.
Open full screen · Exam preparation only: always check the machine's hydraulic schematic, the manufacturer's data and your site lockout procedure.
What this calculator works out
The force a double-acting hydraulic cylinder can push or pull, the pressure a load needs, the rod speed from the pump flow, the hydraulic power, and when the relief valve makes the cylinder stall. Imperial and metric.
The formula in words
Force equals pressure times piston area. Extending, the area is the full bore; retracting, it is the bore area minus the rod area. Rod speed equals flow divided by area: in inches per minute, 231 times the flow in US gallons per minute, divided by the area in square inches. If the load needs more pressure than the relief setting, the cylinder stalls and the pump flow goes over the relief valve as heat.
Worked example
- Imperial: a 4 in bore extending against 15,000 lbf: area = π × 4² ÷ 4 = 12.566 in², so the load needs 15,000 ÷ 12.566 = 1,194 psi. With 10 gpm, speed = 231 × 10 ÷ 12.566 = 183.8 in/min, or 3.06 in/s.
- Metric: a 100 mm bore extending against 60 kN: area = 78.54 cm², so the load needs 60 × 100 ÷ 78.54 = 76.4 bar. With 40 L/min, speed = 10 × 40 ÷ 78.54 = 5.09 m/min, or 84.9 mm/s.
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Rigging, hydraulics, shaft alignment and pumps. The same simulators used in the lessons and the videos.