Definition
A manually operated hydraulic pump that delivers fluid under pressure on both the forward and return strokes of its handle, producing a near-continuous flow rather than pumping only in one direction.
Plain English
A hand pump that pushes fluid out on both the push stroke and the pull stroke of the handle, so you get pressure with every movement instead of only half of them.
Context Anchor
Seen in aircraft hydraulic system descriptions, especially for manual or emergency operation of equipment such as landing gear, brakes, or flaps.
Derivation
Double-acting describes a pump in which both sides of the piston do work — fluid is moved on each direction of travel. A single-acting pump only pumps on one stroke and idles on the other.
Why Pilots Care
Provides a reliable backup method to operate hydraulic systems such as landing gear when engine-driven pumps are unavailable.
Analogy
A simple pump may only do useful work on one movement, like pushing down. A double-acting pump does useful work on both movements, like getting a result from both the push and the pull.
Intuition Check
Do not read “double-acting” as meaning there are two separate pumps. It means one pump delivers fluid on both the push and pull of the handle.
Example Sentence 1
After the main hydraulic pump failed, the technician used the double-acting hand pump to build pressure and extend the landing gear.
Example Sentence 2
During the hydraulic system test, the double-acting hand pump delivered steady pressure on each stroke of the handle.