To test check valve #2 for tightness against backpressure, both the high control valve (which measures pressure downstream of check valve #2) and the bypass control valve (which allows flow around the check valve) must be open. This setup allows the tester to observe whether check valve #2 holds pressure against backpressure conditions, indicating its effectiveness in preventing backflow.
If the tester must open the low control valve more than ¼ turn to achieve the relief opening point, it suggests that shut-off valve #2 is leaking. In a properly functioning assembly, only a slight adjustment should be needed to open the relief valve. A significant turn indicates that the pressure is not being maintained as expected, likely due to a leak in shut-off valve #2.
In a reduced pressure assembly, test cock #3 is typically used to measure pressure downstream of the second check valve, while test cock #2 measures pressure upstream of that valve. If the high side hose is connected to test cock #3 and the low side hose to test cock #2, there should be no pressure difference (differential) indicated on the gauge if both check valves are functioning correctly and there is no backpressure. This means that the assembly is effectively preventing backflow.
If the tester observes that the gauge drops to the low end of the scale and there is discharge from the relief valve after closing shut-off valve #2, it indicates that the assembly is not functioning properly. The relief valve should not discharge under normal testing conditions, as this suggests that there is a failure in the assembly (likely due to a leaking check valve). Consequently, the tester would stop the test and fail the assembly, as it is not compliant with backflow prevention standards.
Regulatory standards typically require that double check valve assemblies be tested at least annually (every 12 months) to ensure they are functioning properly. This routine testing helps prevent contamination of the potable water supply by ensuring that the valves are sealing correctly and preventing backflow.
