A pilot valve is an auxiliary valve,Split-body valve

A pilot valve is an auxiliary valve used to actuate the control mechanism of other valves or components.
Common features of pilot valves:
1)
Together with a fixed hydraulic resistor they form a pilot control bridge that governs the main valve, secondary valve or variable lever according to the input signal.
2)
Flow rate of the primary pilot valve is usually about 1 L/min, maximum 3 L/min; flow of a secondary pilot valve is determined by actual requirements.
3)
Input signals are generally small.
4)
They can accept various input modes: manual, electric, hydraulic, pneumatic, mechanical cam, electro-proportional, etc.
5)
In variable-pump control and similar applications, multiple pilot valves can be combined in modular configurations, allowing easy selection of functions.
6)
A pilot valve itself is often a miniature control valve, most commonly a pressure-control valve.