GB/T 28778-2023Pilot operated safety valves (English PDF)

Foreword

This document was issued on 7 September 2023 by the State Administration for Market Regulation; Standardization Administration of the PRC and takes effect on 1 April 2024.

It is a GB/T standard: recommended rather than compulsory, but it is the text a Chinese reviewer applies when assessing a submission.

1 Scope

GB/T 28778-2023 covers pilot operated safety valves, in which a pilot senses system pressure and drives the main valve instead of a spring loading the main disc directly. It runs from design — the general requirements, the main parts and assemblies, the end connection, the spring and the materials — through the tests a valve passes before it leaves the works: the shell hydraulic test and the shell air pressure test, the adjustment of the cold test differential pressure, the seat sealing test and the airtightness test. Type testing then covers motion performance, the discharge test, and the determination and rating of the coefficient of discharge, which in turn feeds the determination of discharge capacity and the calculation of rated discharge capacity and flow area. Marking and sealing close the document. That order matters because a safety valve is the last barrier when a vessel or a line goes over pressure: one that opens late, chatters, or passes less flow than the sizing calculation assumed leaves the system exposed, a seat that leaks in normal service wastes product and cuts itself, and an unsealed adjustment lets set pressure be moved in the field with nothing left to show it. Written for valve makers, for pressure vessel and pipeline designers sizing relief, for test houses and for inspection bodies.

This document specifies the design, material and structural requirements, ex-factory

tests, type tests, determination of discharge, calculation of rated displacement and flow

area, as well as marking and sealing of pilot operated safety valves.

This document applies to pilot operated safety valves with set pressure not less than 0.1

MPa and flow channel diameter not less than 4 mm.

2 Normative references

The following documents are referred to in the text in such a way that some or all of

their content constitutes requirements of this document. For dated references, only the

version corresponding to that date is applicable to this document; for undated references,

the latest version (including all amendments) is applicable to this document.

GB/T 1047, Pipework components - Definition and selection of nominal size

GB/T 12241, Safety valves - General requirements (GB/T 12241-2021, ISO 4126-

1:2013, MOD)

GB/T 36588, Safety devices for protection against excessive pressure - Common

data (GB/T 36588-2018, ISO 4126-7:2013, MOD)

3 Terms and definitions

Terms and definitions determined by GB/T 1047 and GB/T 12241, as well as the

following, are applicable to this document.

3.1

pilot operated safety valve

A safety valve that is driven or controlled by discharging medium from a pilot valve.

Note: The pilot valve controls the action of the main valve according to the pressure

of the fluid medium. When the medium pressure that keeps the main valve

closed decreases, the pilot safety valve will open. When the medium pressure

closes the pilot valve again, the pilot operated safety valve will close.

3.2