ASCO 3-WAY Valve Operation

Three-way valves have three pipe connections and two orifices. When one orifice is open, he other is closed, and vice versa. They are commonly used to alternately apply pressure to and exhaust pressure from a valve actuator or single-acting cylinder.

Three Types of Operations Apply

Normally Closed (NC) – When the valve is de-energized, the pressure port is closed and the exhaust port is connect to the cylinder port.  When the valve is energized, the exhaust port is closed and the pressure port is connected to the cylinder port.

Normally Open (NO) – When the valve is de-energized, the pressure port is connected to the cylinder port and the exhaust port is closed. When the valve is energized, the pressure port is closed and the cylinder port is connected to the exhaust point.

Universal (Univ) – This allows the to be connect in either the Normally Closed or Normally Open position.  It can also be used to select one of two fluids, or to divert low from one port to another.

ASCO Engineering Guide (PDF)