A hydraulic power unit, or HPU for short, consists of four main components: a prime mover (either an engine or electric motor), a pump, a valve, and a reservoir. Each of these components are constructed together and form the main component in a dump trailer?s hydraulic circuit. Together, these components provide the flow (movement) that the system needs to operate. In order to determine the appropriate HPU for your trailer, you need to consider the following: horse power (HP) of the engine or electric motor power supply (if electric motor), a single or double acting valve, flow (GPM) of the pump, PSI of the system, and capacity of the tank. Most dump trailers use 12V DC motor, which produces 2 HP. The rule of thumb is for every 1 HP you can provide 1 GPM flow at 1500 PSI. The tank of your power unit is sized based on the capacity of your cylinder. Review each component below to learn more.