King Solenoid Valves: Prevention of Liquid Trapping

In many industrial refrigeration systems, the main liquid feed shut off valve (King Valve) can be remotely controlled as a solenoid valve that is interlocked with the computer control system. The typical configuration of a king solenoid valve assembly includes the following four (4) components, listed in the direction of flow:

• Upstream Isolation Valve
• Strainer
• King Solenoid Valve
• Downstream Isolation Valve

This arrangement can offer many advantages over a manually-operated King Valve, but it is important to consider the proper operation of the valve assembly should one of the two manual valves need to be operated in an emergency.

When asked to manually close the King Valve, the impulse of many first responders will be to close the isolation valve closest to the High Pressure Receiver (upstream isolation valve). Careful review of the flow through the solenoid valve, however, illustrates that this will allow liquid ammonia to become trapped between the isolation valve and the solenoid valve if the solenoid valve were to be closed.

Because the solenoid valve is designed to allow for reverse flow when closed, a safer approach to closing the King Valve is to close the downstream isolation valve. When operated this way, liquid cannot be trapped, even if the solenoid valve were to close.

Since it is important that the King Valve be clearly labeled, we suggest installing the label on the isolation valve downstream of the solenoid valve to aid first responders who are not likely to be familiar with the nuances of solenoid valve flow.