The Double Check Valve Device Assembly – Test Cocks and Check Valve Springs

Test Cock # 1 is located upstream of the upstream #1 shut-off valve and is not necessarily used in measuring the differential pressure across the check valves but is use for maintenance purposes and to measure the supply or line pressure. For example, if repairs are need, both the upstream and downstream will need to be shutdown. If water is needed to clean the body of the DCVA or other parts, test cock #1 can be used since it is located on the inlet side of the upstream shut-off valve. In addition, test cock #1 can be used to introduce water slowly into the body of the DCVA during start-up or after a repair. Introducing water slowly into the body of the backflow prevention device will reduce the possibility of introducing debris into the body of the DCVA, which could foul the check valves.

Test cock # 2 is located upstream of first check valve. Test cock # 3 is located between the first and second check valve, downstream of the first check, or upstream of the second check valve. Test cock # 4 is located downstream of the second check valve. This arrangement allows for the measurement of pressure on each side of the check valves. Each check valve shall have a minimum spring load of at least 1 PSI.

Since the DCVA is equipped with spring loaded check valves there is a pressure loss in a static state and a greater pressure loss in a dynamic state (as water flows through the DCVA). The pressure loss through the DCVA is dependent on the size and flow rate of the device. The American Water Works Association maximum allowable pressure loss through the device is 10 PSI for ¼ inch to 12 inch.