Dual checks, on the other hand, are not normally supplied with valves or test cocks. Most are repairable, but many must be removed from service in order to be repaired or tested. For approval, double check valve assemblies must meet rigorous specifications and pass extensive tests including a one-year field evaluation. By contrast, dual check valves are not field tested and are not subjected to the same rigorous testing required of approved backflow preventers. Proponents of reuse systems frequently point out that there is a big difference in the initial cost of dual checks and double checks.
Some manufacturers market dual checks that can be tested and serviced in-line.
However, the costs increase significantly when test cocks and shut-off valves are added to these devices. Some resetters are designed to make servicing dual checks more convenient, but again, this increases the cost of the installation. Approved backflow prevention assemblies should be tested at least annually, as outlined by AWWA M14, the Foundation, and all manufacturers' literature. It seems logical that dual checks should receive more frequent testing, since they do not have to meet the same rigorous approval requirements. A number of them indicated that there were no plans to test or replace these valves.