The hydraulic power unit (HPU) is the assembly consisting of the electric motor, hydraulic pump, oil tank, control valves, and pressure relief devices that generate and regulate the hydraulic pressure used to drive a hydraulic elevator. It is typically installed in a machine room adjacent to the shaft or in the pit. The HPU controls the up and down travel speed through proportional valves and includes temperature monitoring and over-pressure protection. Energy efficiency improvements in modern HPUs include variable-speed pump motors.