Which test cocks must be open to test the differential pressure drop across check valve number one on a double check?

To test the differential pressure drop across the first check valve on a double check assembly, it's essential to leverage the appropriate test cocks. In this scenario, test cocks two and three are the ones that need to be open.

The double-check valve assembly consists of two check valves and test cocks connected to each. When testing the pressure drop across the first check valve, you strategically open test cock two (downstream of the first check valve) to measure the pressure downstream of the valve and test cock three (upstream of the first check valve) to measure the pressure upstream. By doing this, you can accurately calculate the differential pressure across the first check valve, which is critical for determining its operational efficacy.

Opening test cock one is unnecessary in this case because it is positioned upstream of the first check valve, while test cock four relates to the second check valve. Therefore, using the correct combination of test cocks allows for a precise assessment of the check valve’s performance, enabling potential issues to be identified effectively.