Expilot is a term used to describe a solenoid-pilot directional control valve utilizing an external pilot signal. A pilot signal, often referred to as the pilot pressure, creates the force required to do work in the main body pilot valve. Solenoid-pilot valves utilize an internal or an external source for its pilot signal.
An internal pilot source utilizes the main body media as the source of the pilot signal. A valve that uses an external pilot source does not utilize the main body media rather requires a separate, external pressurized source for the pilot signal.
An expilot design is common when the pressure of controlled media does not meet the minimum pressure requirement of the main valve or where the control media need to be separated from the main body media.