Hydraulic power pack (HPU)

A hydraulic power pack (HPU), or hydraulic power unit, is a self-contained skid of pumps, motor, reservoir, and valves that supplies pressurized oil to deck and steering machinery. It holds one or more variable-displacement axial-piston pumps driven by electric motors, a filtered oil tank, accumulators, relief and directional valves, and a cooler, delivering oil at 150 to 350 bar to actuators. On a ship the HPU powers the steering-gear rams, hatch covers, deck cranes, windlasses, and watertight doors, with duplicated pumps and power feeds so a single failure does not lose steering.