Sprinkler Age A Publication of the American Fire Sprinkler Association
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A Type-II bypass valve is a modern enhancement used in detector backflow assemblies. These detector assemblies are crucial because they divert a portion of flow through a bypass that includes a water meter, allowing system operators to detect hidden leaks or unauthorized water use. Unlike traditional Type-I bypasses where both the main assembly and the bypass line include two check valves, the Type-II layout uses just one check valve in the bypass. This streamlined configuration connects upstream and downstream of the main assembly’s second check valve, providing equivalent protection to the older Type-I design but with fewer components.
Consistent Size, Unified Maintenance
One of the most practical benefits of the Type-II bypass is its uniform sizing: the bypass line is always ¾ inch, regardless of the mainline assembly’s size. This standardization simplifies installation and maintenance, as technicians can rely on the same repair kits and testing procedures across all Type-II assemblies. This consistency results in more efficient fieldwork, easier stocking of parts, and faster service turnaround.
Lean Design and Enhanced Flow
By eliminating one check valve in the bypass line, the Type-II configuration reduces friction loss, allowing for more efficient water flow. In fire protection systems, where maintaining optimal pressure is essential, this improved hydraulic performance translates into better reliability during emergencies. Additionally, with fewer parts to manage, there are fewer potential points of failure, contributing to long-term system reliability.
Why a Bypass Is Needed
Detector assemblies use meter-equipped bypass lines primarily in fire sprinkler systems. Since sprinklers require steady, high pressure, installing a meter directly on the mainline can compromise system readiness. Instead, the bypass arrangement lets water flow through the meter only when needed, making it possible to detect leaks or unauthorized use without impeding pressure. This setup is especially beneficial in urban systems where such misuse is more likely.
Regulatory Approval and Testing Standards
The Type-II bypass design was adopted in the mid-2000s when both the American Society of Sanitary Engineering (ASSE) and the USC Foundation for Cross–Connection Control and Hydraulic Research (Foundation) updated their detector assembly standards, introducing RPDA-II and DCDA-II configurations that incorporate a single check valve in the bypass. These bodies treat the Type-II detector assembly as a single unit, with one test report covering the entire system (rather than separate reports for the mainline and bypass).
RPDA-II tests include: Check Valve #1, Check Valve #2, Relief Valve opening, and the Single Bypass Check. DCDA-II tests include: Check Valve #1, Check Valve #2, and the Single Bypass Check.
Specifically, the Foundation requires the bypass’s single check to hold a minimum of 1.0 psi differential, while ASSE standards mandate that it hold tight against backpressure (with a minimum of 0.5 psi for DCDA-II).
Summary of Benefits
By adopting the Type-II bypass design, fire protection systems gain:
- Simplified testing and documentation — one standardized report for the entire assembly.
- Easier maintenance and parts handling thanks to a uniform bypass size of ¾ inch.
- Improved hydraulic efficiency due to fewer check valves in the bypass.
- Lower risk of failure, with streamlined assembly and access.
- Full regulatory approval under modern ASSE and Foundation standards.
A Modern Solution for Detector Assemblies
The Type-II bypass valve represents a refined approach to detector assembly design. By integrating a single check valve into a simplified bypass layout and adhering to uniform sizing, it maintains robust protection while enhancing serviceability and performance. For engineers, inspectors, and maintenance professionals tasked with ensuring fire system integrity, embracing Type-II detector assemblies is a practical and forward-looking choice.
Why Choose Backflow Direct for Type-II Bypass Valves
Backflow Direct makes it easy to take advantage of the performance and reliability benefits of Type-II bypass valves. Our assemblies, including the Deringer 30 and 50 series, are built with a ¾-inch standardized bypass, single check design, and field-friendly features that simplify testing and maintenance. By purchasing directly from Backflow Direct, you gain access to industry-leading products, straightforward online ordering, and expert technical support. Whether you are an engineer specifying assemblies, a contractor installing them, or a water authority overseeing compliance, Backflow Direct provides the trusted solutions you need to protect your systems with confidence.