Power transfer unit

In aviation, a power transfer unit (PTU) is a device that transfers hydraulic power from one of an aircraft's hydraulic systems to another in the event that second system has failed or been turned off.

Modern airliners have separate, independent hydraulic systems powered by engine-driven pumps. The PTU is used when, for example, there is right hydraulic system pressure but no left hydraulic system pressure. The PTU transfers hydraulic power from the right hydraulic system to the left hydraulic system; there is no intermixing of hydraulic fluid between the left and right hydraulic systems during PTU operation.