Which valves need to be closed to perform testing on a DCVA?

To perform testing on a Dual Check Valve Assembly (DCVA), it is necessary to close both check valves. This is because the purpose of the testing is to ensure that both check valves are functioning properly and preventing backflow. Closing both valves allows for an accurate assessment of the integrity of the assembly under test conditions.

When performing these tests, if only one valve is closed, the system cannot be adequately evaluated for backflow conditions, which could lead to undetected failures or issues. The testing process typically involves verifying that each valve can effectively seal against backpressure, and this requires isolating the assembly from the system entirely by closing both valves. Thus, closing both check valves is essential for comprehensive and reliable backflow prevention testing.

The other choices suggest actions that would not provide the necessary control over the backflow situation for a complete evaluation. For example, closing only one valve would not allow for a full understanding of how the complete assembly functions under pressure.