Definition
The pressure at which a pressure-controlled device, such as an engine-driven hydraulic or pneumatic pump unloader valve, automatically activates and begins delivering pressure back into the system. It marks the lower setting of a regulated pressure range, with the system cycling between this kick-in value and a higher kick-out value.
Plain English
The pressure level that is low enough to switch the pump back on. When system pressure drops to this number, the device starts pumping again to bring pressure back up.
Context Anchor
Seen in aircraft system descriptions and maintenance checks for hydraulic, pneumatic, or other pressure-controlled systems.
Derivation
From the everyday phrase 'kick in,' meaning to start working or come into action. The pressure 'kicks in' the pump.
Why Pilots Care
Knowing the kick-in pressure helps technicians and pilots verify that a hydraulic or pneumatic system is cycling within its correct operating range. A kick-in pressure that drifts low or high signals a regulator problem and can lead to weak system performance or component damage.
Intuition Check
Kick-in pressure is not a pressure spike or a physical kick. It is the set point where the system starts a pump or compressor.
Example Sentence 1
After the gear was retracted, hydraulic pressure dropped to the kick-in pressure and the pump cycled on to recharge the system.
Example Sentence 2
If system pressure falls too low, the pump engages at its kick-in pressure to prevent loss of flight control authority.