Pilot-operated safety valves
1 Scope
This standard specifies the terms and definitions, the design, material and construction requirements, the test, the determination of the theoretical discharge capacity, the calculation of certified discharge capacity and examples for calculation of flow area, and the marking and sealing of the pilot-operated safety valves.
This standard is applicable to pilot-operated safety valves having a set pressure not less than 0.1 MPa and a flow diameter not less than 6 mm. This standard does not place limitation on the applicable temperature of the pilot-operated safety valves.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GB/T 7306.1 Pipe threads with 55 degree thread angle where pressure-tight joints are made on the threads—Part 1: Parallel internal and taper external threads (GB/T 7306.1-2000, eqv ISO 7-1: 1994)
GB/T 7306.2 Pipe threads with 55 degree thread angle where pressure-tight joints are made on the threads—Part 2: Taper internal and external threads (GB/T 7306.2-2000, eqv ISO 7-1: 1994)
GB/T 9113 Integral steel pipe flanges
GB/T 12224 General requirements for industrial steel valves (GB/T 12224-2005, ASME B16.34a: 1998, NEQ)
GB/T 12241 Safety valves—General requirements (GB/T 12241-2005, ISO 4126-1: 1991, MOD)
GB/T 12716 Pipe threads with the thread angle of 60 degrees where pressure-tight joints are made on threads (GB/T 12716-2002, ASME B1.20.1: 1992, EQV)
GB/T 17241.6 Integral cast iron flanges
GB/T 21465 Terminology for valves
JB/T 2769 Components of valves—High pressure threaded flanges
ISO 4126-7: 2004 Safety devices for protection against excessive pressure—Part 7: Common data
3 Terms and definitions
For the purposes of this document, the terms and definitions given in GB/T 12241 and GB/T 21465 and the following apply.
3.1 Types of pilot
3.1.1
flowing pilot
pilot in which the fluid flows throughout the relieving cycle of the pilot-operated safety valve
3.1.2
non-flowing pilot
pilot in which the fluid flows only during the opening and/or closing of the pilot-operated safety valve
3.2 types of action of the pilot-operated safety valve
3.2.1
open/close
action characterized by stable operation resulting in fully open or fully closed main valve position
3.2.2
modulating
action characterized by a gradual opening and closing of the disc of the main valve which is a function of the pressure, proportional but not necessarily linear
3.3 Pressure
3.3.1
maximum allowable pressure
maximum pressure for which the equipment is designed as specified by the manufacturer
3.3.2
opening sensing pressure
pressure at which the pilot commences to open in order to achieve the set pressure
3.4 Discharge capacity
3.4.1
theoretical discharge capacity
calculated capacity expressed in mass or volumetric units of a theoretically perfect nozzle having a cross-sectional flow area equal to the flow area of a main valve of the pilot-operated safety valve
3.4.2
coefficient of discharge
value of specific discharge capacity divided by the theoretical discharge capacity
4 Design, material and construction requirements
4.1 General
4.1.1 Design, materials and construction of pilot-operated safety valves shall meet the requirements of GB/T 12241.
4.1.2 A guide mechanism shall be designed to ensure the reliability of action and sealing.
4.1.3 The seat and body of the main valve may be integral or split. The split seat shall be reliably fixed on the body, and the seat shall be free from looseness when the valve is opened and closed.
4.1.4 Means shall be provided to lock and/or to seal all external adjustments and no adjustment shall be made to the pilot-operated safety valves without the permission of the manufacturer.
4.1.5 In the case of main valves with restricted lift, the lift restricting device shall limit the main valve lift but shall not otherwise interfere with the operation of the main valve. The lift restricting device shall be designed so that, if adjustable, the adjustable feature can be mechanically locked and sealed. The lift restricting device shall be installed and sealed by the valve manufacturer. Valve lift shall not be restricted to a value less than 1 mm.
4.1.6 Pilot-operated safety valves for toxic or flammable fluids shall have the pilot vented to a safe place.
4.1.7 The main valve shall be provided with a drain connection at the lowest point where liquid can collect unless other provisions for draining are provided.
4.1.8 The design stress of load carrying parts shall meet the requirements of relevant standards.
4.1.9 In the case of failure of any sealing elements, the pilot-operated safety valve shall discharge its certified discharge capacity at not over 1.1 times the maximum allowable pressure of the equipment to be protected.
Foreword i
1 Scope
2 Normative references
3 Terms and definitions
3.1 Types of pilot
3.2 types of action of the pilot-operated safety valve
3.3 Pressure
3.4 Discharge capacity
4 Design, material and construction requirements
4.1 General
4.2 Main components
4.3 End connections
4.4 Spring
4.5 Materials
5 Test
5.1 End-of-manufacturing test
5.2 Tests to determine operating characteristics and discharge capacity
6 Determination of the theoretical discharge capacity
6.1 Determination of the coefficient of discharge
6.2 Critical and subcritical flow
6.3 Discharge capacity at critical flow
6.4 Theoretical discharge capacity at subcritical flow
6.5 Theoretical discharge capacity in the turbulent zone where the Reynolds number is equal to or greater than 80,000
7 Calculation of certified discharge capacity and examples for calculation of flow area
7.1 General
7.2 Calculation of certified discharge capacity
7.3 Examples for calculation of flow area
8 Marking and sealing
8.1 Marking
8.2 Sealing
Annex A (Normative) Symbols and units
Annex B (Informative) Examples for calculation of flow area for various media
Annex C (Informative) Comparison between references
Annex D (Informative) Correspondence between this standard and ISO 4126-4: 2004
