Definition
The pressure setting at which an unloading valve in a hydraulic system stops directing pump output to the system and begins routing it back to the reservoir at low pressure. When the system reaches kick-out pressure, the pump is effectively unloaded so it does not have to work against full system pressure when no demand is present.
Plain English
It is the pressure at which a hydraulic pump stops pushing fluid into the system and starts sending it back to the tank instead. Once the system is full and pressurized, the pump is given a break until the pressure drops again.
Context Anchor
Seen in aircraft hydraulic system maintenance, especially when checking pump control, pressure switches, or unloading valves.
Derivation
The term comes from the everyday sense of 'kick out' meaning to push something away or send it elsewhere. At this pressure the valve 'kicks' the pump's output away from the system and sends it back to the reservoir.
Why Pilots Care
Kick-out pressure protects the hydraulic system from over-pressurization and reduces wear on the pump. A pump that does not unload properly will run constantly against full pressure, generating heat and shortening component life.
Analogy
It is like an air compressor that shuts off when the tank reaches its set pressure. The pump has done enough, so the control stops it from building more pressure.
Intuition Check
Kick-out pressure does not mean a sudden failure or a part being physically kicked out. It means the normal pressure point where the system automatically stops adding pressure.
Example Sentence 1
When the hydraulic system reached kick-out pressure, the unloading valve opened and routed pump output back to the reservoir.
Example Sentence 2
Low kick-out pressure prevented the landing gear from extending fully because the pump unloaded too soon.