The HANST Interface valve is a two-position, three-position normally closed valve that uses a low-pressure pilot to control the opening of the high-pressure circuit and a spring-return flow control valve. Its function is to use a relatively low pilot pressure to control the high-pressure hydraulic output. When the pilot pressure is released, the inlet is closed and the pressure in the control circuit is relieved. The hydraulic three-way valve is commonly used to control the opening or closing operation of subsurface safety valves (SCSSVs) or surface safety valves (SSVs).