The valve positions used in this description are defined as follows:
Back-Seated – Valve stem turned all the way out (fully counterclockwise).
Front-Seated – Valve stem turned all the way in (fully clockwise).
NOTE: The port numbers shown have been arbitrarily assigned for the purpose of this description.
Used for normal system operation. Valve is fully opened. Flow of the system refrigerant is unrestricted through the valve via ports 1 and 2. The direction of flow through the valve depends on its placement (low side or high side) in a system. A Schrader valve service port is at the prevailing system pressure, but is closed off.
Access to the system is provided through the Schrader valve. This allows measurement of the system pressure that exists at the valve. It also allows access to the system components on both sides of the valve for the purpose of evacuation, recovery, and charging.
Path between ports 1 and 2 is closed, resulting in no refrigerant flow through the valve.
System components on the port 1 side of the valve are isolated from those on the port 2 side. However, the enlarged area around the valve plug enables the refrigerant at port 1 to be applied at the Schrader valve. This allows the measurement of the system pressure that exists on the port 1 side of the valve. It also makes the system components on the port 1 side of the valve accessible for the purpose of evacuation and refrigerant recovery or charging.