Wilkins Backflow Preventers: Models and Applications

Wilkins, a brand operating under Zurn Industries, manufactures a broad line of backflow prevention assemblies used across residential, commercial, and industrial water systems in the United States. This page covers the principal Wilkins product lines, their mechanical designs, applicable hazard classifications, and the regulatory and installation contexts where each model is typically specified. Wilkins assemblies are tested and listed under ASSE International standards and evaluated through the USC Foundation for Cross-Connection Control and Hydraulic Research, making them eligible for specification under the plumbing codes adopted by water authorities nationwide. The Backflow Listings section of this resource provides additional context on assembly approvals and installer qualifications.

Definition and scope

Wilkins backflow preventers are mechanical assemblies designed to protect potable water supplies from contamination caused by reverse flow events — either backpressure or backsiphonage — at cross-connection points in a distribution system. The brand's product catalog spans four primary assembly types recognized under ASSE International standards and the USC Manual of Cross-Connection Control:

  1. Reduced Pressure Zone (RPZ) Assembly — governed by ASSE 1013
  2. Double Check Valve Assembly (DCVA) — governed by ASSE 1015
  3. Pressure Vacuum Breaker (PVB) — governed by ASSE 1020
  4. Atmospheric Vacuum Breaker (AVB) — governed by ASSE 1001

Listing under the USC Foundation for Cross-Connection Control and Hydraulic Research (USC FCCCHR) is a prerequisite for approval under the plumbing codes adopted by most US water authorities and municipalities. Wilkins assemblies are also evaluated against standards published by ASSE International, whose product performance standards define the minimum mechanical requirements for each device class.

The U.S. Environmental Protection Agency's Cross-Connection Control Manual identifies device selection as contingent on hazard degree — a classification boundary that separates high-hazard applications (requiring RPZ protection) from low-hazard applications (eligible for DCVA or vacuum breaker protection). Wilkins product lines map directly onto this classification framework.

How it works

Wilkins assemblies function by interrupting reverse flow at a cross-connection point using one or more internal check mechanisms. The specific mechanical approach differs by device type.

Reduced Pressure Zone (RPZ) — Wilkins 975XL and 375 series
The RPZ assembly contains 2 independently acting, spring-loaded check valves separated by a reduced pressure zone. A differential pressure relief valve vents to atmosphere if the pressure between the two checks falls below supply pressure by a specified threshold — typically 2 pounds per square inch differential (psid). This relief mechanism provides a physical break in the water column, qualifying the RPZ as the highest protection class under ASSE 1013. The Wilkins 975XL is designed for 2½-inch through 10-inch pipe sizes; the compact 375 series addresses ¾-inch through 2-inch applications.

Double Check Valve Assembly (DCVA) — Wilkins 950XL and 350 series
The DCVA uses 2 independently acting check valves in series, without a relief valve or reduced pressure zone. Both checks must fail simultaneously for backflow to occur, but the assembly lacks the redundant venting protection of an RPZ. ASSE 1015 governs this class. DCVAs are approved only for low-hazard cross-connections; they are not acceptable where a health hazard (toxic or biological contamination potential) exists.

Pressure Vacuum Breaker (PVB) — Wilkins 720A series
The PVB incorporates a spring-loaded check valve and an air inlet valve that opens under negative pressure conditions, breaking the siphon. Governed by ASSE 1020, PVBs must be installed at least 12 inches above the highest downstream outlet and are not approved for continuous pressure applications. The Wilkins 720A is commonly specified for irrigation systems.

Atmospheric Vacuum Breaker (AVB) — Wilkins 70 series
The AVB is the least protective device class — governed by ASSE 1001 — and functions only where pressure is not continuously applied. A single air inlet opens when supply pressure drops, preventing backsiphonage. AVBs are not testable in the field and are not approved for high- or low-hazard health risk applications.

Common scenarios

Wilkins assemblies appear across a broad range of installation contexts. Device selection in each scenario depends on the hazard classification assigned to the cross-connection by the authority having jurisdiction (AHJ).

Irrigation and landscape systems: PVBs (Wilkins 720A) are the predominant device type for residential and light commercial irrigation where the downstream piping is not subject to continuous pressure. Where a health hazard exists — such as a fertilizer injection system — an RPZ is required regardless of system size.

Fire suppression systems: Wilkins 950XL DCVAs are widely specified for sprinkler systems where the fire suppression water does not contain antifreeze or other chemical additives. Where chemical additives are present, the AHJ typically requires RPZ protection under NFPA 13, the Standard for the Installation of Sprinkler Systems (NFPA).

Commercial and industrial process connections: High-hazard cross-connections — chemical feed lines, cooling towers, medical equipment supply — require RPZ assemblies. The Wilkins 975XL series covers large-diameter commercial mains from 2½ inches through 10 inches.

Multifamily residential service lines: DCVAs at the service entry point are specified for residential buildings where the hazard classification is low. Local water authority requirements govern whether a DCVA or RPZ is mandated at the meter.

For guidance on how assembly types connect to tester qualifications and utility programs, the backflow directory purpose and scope provides a structured overview of how the service sector is organized.

Decision boundaries

Selecting the correct Wilkins assembly requires resolving four decision points in sequence:

  1. Hazard classification — The AHJ determines whether the cross-connection presents a health hazard (high hazard) or a non-health hazard (low hazard). High-hazard connections mandate RPZ assemblies; low-hazard connections may qualify for DCVA or vacuum breaker protection. The EPA Cross-Connection Control Manual and USC FCCCHR Manual of Cross-Connection Control provide the standard reference frameworks for this determination.

  2. Backflow mechanism — Backsiphonage-only risk (as in non-pressurized irrigation downstream) permits vacuum breaker solutions. Backpressure risk requires either a DCVA (low hazard) or RPZ (high hazard), as vacuum breakers provide no backpressure protection.

  3. Continuous pressure requirement — PVBs and AVBs are prohibited where continuous pressure exists downstream. Any application with valves downstream of the device constitutes a continuous pressure condition and eliminates vacuum breaker eligibility under ASSE 1020 and ASSE 1001 respectively.

  4. Pipe size and pressure rating — Wilkins product lines are segmented by pipe diameter and working pressure. The 975XL series is rated to 175 psi working pressure in sizes 2½ inches through 10 inches. The 375 series addresses ¾-inch through 2-inch applications in the same pressure class. Mismatching pipe size to product series is a common installation error that affects testability and code compliance.

Field testing requirements are a separate compliance obligation from device selection. RPZ and DCVA assemblies must be tested at installation and on a periodic schedule — typically annually — by a certified backflow assembly tester (BAT) recognized by the AHJ. AVBs are not field-testable and cannot satisfy test-on-installation requirements. The how to use this backflow resource page describes how tester listings and certification verification are structured within this reference network.

References

📜 1 regulatory citation referenced  ·  ✅ Citations verified Feb 26, 2026  ·  View update log

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