Definition
A manually operated hydraulic pump that moves fluid on both the forward and return strokes of its handle, producing a continuous flow of pressurized fluid in the system rather than only on one stroke direction.
Plain English
A hand-operated pump that pushes hydraulic fluid through the system on every movement of the handle — push or pull — instead of only one direction.
Context Anchor
Seen in aircraft hydraulic system discussions, especially for backup or emergency operation of equipment such as landing gear, flaps, or brakes.
Derivation
‘Double-acting’ describes a pump that does work in two directions of its stroke. The contrast is a single-acting pump, which only pumps fluid on one direction of the handle and rests on the return. Knowing this distinction is the whole point of the term.
Why Pilots Care
Allows hydraulic systems to be pressurized manually when engine-driven pumps are unavailable, supporting emergency gear extension or ground servicing.
Analogy
It is like a hand pump that sends water out when you push the handle and also when you pull it back, instead of wasting half the motion.
Intuition Check
Do not read “double-acting” as meaning the pump has two separate jobs. Here it means the pump moves fluid on both strokes of the handle.
Example Sentence 1
After the hydraulic pump failure, the pilot used the double-acting hand pump to lower the landing gear before landing.
Example Sentence 2
With the engine shut down, the double-acting hand pump supplied pressure to cycle the flight controls on the ground.