GB/T 25178-2020Reduced-pressure type backflow preventer (English PDF)

Foreword

This standard was drafted in accordance with the rules given in GB/T 1.1-2009.

This standard replaces GB/T 25178-2010 "Decompression Backflow Preventer", compared with GB/T 25178-2010, except for editorial changes The main technical changes are as follows:

---Modified terms and definitions such as "pressure-reducing backflow preventer", "zero flow" (see 3.1~3.5, 3.1~3.5 in 2010 edition);

--- Deleted the terms and definitions of "independently acting check valve" and "PN (nominal pressure)" (see 3.6 and 3.7 of the 2010 edition);

---Added the terms and definitions of "initial release pressure difference" (see 3.6);

---The content of Chapter 5 of the 2010 edition was changed to Chapter 4, and the model designation was revised (see 4.2, 5.1 of the 2010 edition);

---The contents of Chapter 4 and Chapter 6 of the 2010 edition are merged into Chapter 5, and the requirements for detecting ball valves are modified (see 5.2.3, 6.2, 2010 edition 4.1.2);

---Modified the online maintenance requirements (see 5.2.4, 4.1.3 of the 2010 edition);

---The structural design requirements of the drain valve have been moved from 7.10.1 in the 2010 edition to 5.2.5 (see 5.2.5 and 7.10.1 in the 2010 edition);

---The requirements for the shut-off valve in Appendix A of the 2010 edition have been moved to 5.2.6, and the sealing form requirements of the shut-off valve have been added (see 5.2.6, Appendix AA 2 of the 2010 edition);

---Modified the connection form requirements in the structural form (see 6.2.4, 4.2 in the 2010 edition);

---The appearance and painting requirements and test methods have been revised (see 6.1, 7.1, 2010 edition of 7.4, 8.1.2);

---Modified the strength requirements (see 6.3, 7.7 in the 2010 edition);

---Modified the performance requirements of the check valve (see 6.4, 7.8 in the 2010 edition);

---Modified the hydraulic characteristics requirements (see 6.5, 7.9 in the 2010 edition);

---Revised the pressure loss requirements (see 6.6, 7.9.3 of the 2010 edition);

---Modified the performance requirements of the drain valve (see 6.7, 7.10 in the 2010 edition);

---Added the sensitivity performance requirements and test methods of the drain valve (see 6.7.2, 7.7.2);

---Added cyclic test, hygiene requirements and test methods (see 6.9, 6.10, 7.9, 7.10);

---Modified the water inlet pressure during the hydraulic characteristic test, pressure loss test, and discharge valve opening and closing performance test. The test device diagram was moved to the attached Record B (see 7.5, 7.6, 7.7.1, Appendix B, 8.3~8.9 of the 2010 edition);

---Modified the factory inspection items (see 8.2, 9.1 of the 2010 edition);

---Modified the type test and sampling rules (see 8.3, 9.2, 9.3 of the 2010 edition);

---Modified the product mark (see 9.2, 10.2 of the 2010 edition).

1 Scope

This standard specifies the terms and definitions, classification, model marking, materials and structure, requirements, test methods, and inspections of pressure-reducing backflow preventers Rules, signs, packaging, storage and transportation.

This standard is suitable for conveying the nominal pressure not greater than PN16, the nominal size DN15~DN400, and the medium temperature not higher than 65°C decompression type backflow preventer for water use (hereinafter referred to as "backflow preventer").

2 Normative references

The following documents are indispensable for the application of this document. For dated reference documents, only the dated version applies to this document. For undated references, the latest version (including all amendments) applies to this document.

GB/T 196 basic size of ordinary thread

GB/T 1047 Definition and Selection of Nominal Dimensions of Piping Components

GB/T 1048 Definition and selection of nominal pressure of pipeline components

GB/T 1732 Test Method for Impact Resistance of Paint Film

GB/T 3098.1 Mechanical properties of fasteners bolts, screws and studs

GB 5135.11 Automatic sprinkler system Part 11: Groove type pipe joint

GB/T 5210 Paint and varnish pull open adhesion test

GB/T 6739 Paint and varnish pencil method for determination of paint film hardness

GB/T 7306.2 55° Sealed Pipe Thread Part 2: Conical Internal Thread and Conical External Thread

GB/T 9124.1 Steel pipe flanges Part 1: PN series

GB/T 12220 Industrial valve mark

GB/T 12225 General Valve Copper Alloy Casting Technical Conditions

GB/T 12227 Technical conditions for general valve ductile iron castings

GB/T 12230 General valve stainless steel casting technical conditions

GB/T 13452.2 Determination of film thickness of paints and varnishes

GB/T 13927 Industrial valve pressure test

GB/T 17219 Safety evaluation standard for drinking water distribution equipment and protective materials

GB/T 17241.6 Integral cast iron flange

GB/T 17241.7 Technical conditions for cast iron pipe flanges

GB/T 20878 Stainless steel and heat-resistant steel grades and chemical composition

GB/T 21873 Rubber Sealing Material Specification for Interface Sealing Rings for Water Supply, Drainage and Sewage Pipes

GB/T 24588 Stainless steel spring wire

GB/T 26640 Specification for minimum wall thickness of valve housing

CJ/T 216 Soft Seal Gate Valve for Water Supply and Drainage

JB/T 7927 Appearance quality requirements of valve steel castings

JB/T 7928 Industrial valve supply requirements