Type-II bypass valve explained

What is a Type-II Bypass?

A type-II bypass is used on a detector backflow assembly, which consists of a main valve, with 2 checks, and a bypass valve, with either 2 checks (standard type-I bypass) or 1 check (modern type-II bypass). The type-II bypass valve connects upstream and downstream of the main second check valve. Although it has fewer components, the type-II bypass provides the same backflow protection as the type-I.

The type-II bypass is always a ¾” pipe, no matter the size of the backflow assembly main valve. The same repair kit can be used for any size Deringer 30 or 50. Also, less components means the check valves are easier to access and remove. Testing is streamlined too, since all type-II bypass valves are the same. We have videos for how to test a type-II bypass for both USC testing and ASSE testing.


How does a double check detector assembly work?

Type-II Bypass Explained

Benefits of a type-II bypass

  • Less check valves = less friction loss and more pressure
  • All type-II bypasses are ¾” = the same testing and repair procedures for any type-II bypass
  • Less components = less potential points of failure and easier maintenance and repair


Why does a backflow preventer need a bypass valve?

The bypass valve diverts some of the flow of water from the main valve, through the bypass valve. Attached to the bypass valve is a bypass water meter, which detects unusual flow of water. Hence, why we call them detector assemblies.

Detector assemblies will tell you if there is a leak or if someone is stealing your water. They’re mostly used in fire sprinkler systems, because putting a water meter on the system can cause pressure loss, and fire sprinkler systems have stringent requirements for water pressure. Detector assemblies are also used more often in cities, where it’s more likely that someone would steal water from your system.  

Typically, your fire marshal or water district decides whether your project needs a detector assembly or a standard DC or RP assembly.


Watch the videos below on our YouTube channel, to learn more about DCDA-II and RPDA-II, including how to fill out a test report for a type-II bypass backflow assembly. 

About the DCDA-II Backflow Preventer

About the RPDA-II Backflow Preventer