What check should a technician perform to determine if the check valve of a flow control valve (FCV) is stuck open?

To ascertain if the check valve of a flow control valve (FCV) is stuck open, closing the needle valve completely and checking the metered flow is essential. When the needle valve is fully closed, there should be minimal or no flow through the system if the check valve is functioning correctly. However, if the flow continues even when the needle valve is closed, it strongly indicates that the check valve is not sealing properly and is, therefore, likely stuck in the open position. This method provides a clear indication of whether or not the check valve is performing its intended function of preventing backflow.

Monitoring the actuator for movement, visually inspecting the check valve, or measuring the flow rate with a gauge may not provide the conclusive results needed to assess if the check valve is stuck. Each of these alternatives could lead to ambiguous results, as they do not directly test the check valve's ability to block flow when required.