GB 3446-2026 Siamese connection English, Anglais, Englisch, Inglés, えいご
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ICS
CCS
National Standard of the People's Republic of China
GB/T 3446-2026
Siamese connection
消防水泵接合器
Issue date: 2026-01-28 Implementation date: 2027-02-01
Issued by the General Administration of Quality Supervision, Inspection and Quarantine of the People's Republic of China
the Standardization Administration of the People's Republic of China
Contents
Foreword
1 Scope
2 Normative References
3 Terms and Definitions
4 Classification
4.1 Types and Specifications
4.2 Model Designation
5 Technical Requirements
5.1 Construction
5.2 Materials
5.3 Appearance Quality
5.4 Threads
5.5 Connection Methods
5.6 Handwheel
5.7 Lifting Height
5.8 Sealing Performance
5.9 Hydrostatic Strength Performance
5.10 Valves
5.11 Fire Fighting Coupling
6 Test Methods
6.1 Construction Inspection
6.2 Material Inspection
6.3 Appearance Quality Inspection
6.4 Thread Dimension Inspection
6.5 Handwheel Test
6.6 Lifting Height Test
6.7 Sealing Performance Test
6.8 Hydrostatic Strength Performance Test
6.9 Safety Valve Opening Pressure and Opening/Closing Differential Pressure Test
6.10 Fire Fighting Coupling Performance Inspection
7 Inspection Rules
7.1 Type Inspection
7.2 Factory Inspection
8 Marking
9 Packaging
Siamese connection
1 Scope
This document defines the terms for siamese connection, specifies classification, technical requirements, inspection rules, marking and packaging, and describes the corresponding test methods.
This document applies to various types of siamese connection used in fire protection piping systems.
2 Normative References
The contents of the following documents constitute essential provisions of this document through normative reference. For dated references, only the edition cited applies. For undated references, the latest edition (including all amendments) applies.
GB/T 197 General purpose metric screw threads — Tolerances
GB/T 1176 Cast copper and copper alloys
GB/T 1348 Spheroidal graphite iron castings
GB/T 1804-2000 General tolerances — Tolerances for linear and angular dimensions without individual tolerance indications
GB/T 4423 Copper and copper alloy drawn rods
GB 5135.11 Automatic sprinkler system — Part 11: Grooved fittings
GB/T 7307 55° non-sealing pipe threads
GB/T 9124.1 Steel pipe flanges — Part 1: PN series
GB/T 9439 Grey iron castings
GB 12514 (all parts) Fire fighting coupling
GB/T 17241.1 Cast iron pipe flanges — Part 1: PN series
JB/T 7273.3 Handwheels
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1 siamese connection
A connection device fixedly installed outside a building, used for fire trucks or mobile pumps to deliver fire water and other liquid fire extinguishing agents into the building's internal fire protection water supply system.
Note: Hereinafter referred to as "connection".
4 Classification
4.1 Types and specifications
4.1.1 The installation types of siamese connection are classified as above-ground type, underground type, wall type and multi-purpose type.
4.1.2 The installation types of multi-purpose siamese connection are classified as above-ground multi-purpose type and underground multi-purpose type.
4.1.3 The nominal sizes of the outlet ports of siamese connection are classified as DN100 and DN150.
4.1.4 The rated working pressures of siamese connection are classified as 1.6 MPa, 2.5 MPa and 4.0 MPa.
4.1.5 The connection types of siamese connection are classified as flanged type and grooved type.
4.2 Model designation
The model designation method for siamese connection is as follows:
Example 1: An above-ground type siamese connection with a nominal size of DN100, a rated working pressure of 1.6 MPa and a flanged connection is designated as: SQS100-1.6.
Example 2: An above-ground multi-purpose type siamese connection with a nominal size of DN150, a rated working pressure of 2.5 MPa and a grooved connection is designated as: SQSD150-2.5G.
5 Technical requirements
5.1 Construction
5.1.1 The siamese connection shall consist of a body, fire fighting couplings, a safety valve, and non-return and shut-off devices. The construction shall ensure that residual water between the fire fighting coupling and the non-return device is completely drained after use.
5.1.2 For multi-purpose siamese connections, the non-return device shall be installed on the body and shall not affect the normal use of the fire fighting couplings.
5.1.3 The construction of the siamese connection shall ensure that the minimum internal flow area of the connection in use is not less than the total flow area of all inlet fire fighting couplings.
5.2 Materials
5.2.1 For siamese connections with a rated working pressure of 1.6 MPa, the body and the handwheel of multi-purpose siamese connections shall be made of grey cast iron HT200 conforming to GB/T 9439, or other metal materials with mechanical properties not lower than those of HT200.
5.2.2 For siamese connections with a rated working pressure of 2.5 MPa, the body shall be made of spheroidal graphite iron QT 400-18 conforming to GB/T 1348, or other metal materials with mechanical properties not lower than those of QT 400-18.
5.2.3 For siamese connections with a rated working pressure of 4.0 MPa, the body shall be made of spheroidal graphite iron QT 450-10 conforming to GB/T 1348, or other metal materials with mechanical properties not lower than those of QT 450-10.
5.2.4 The fire fighting coupling body at the inlet of the siamese connection, the valve seat and the stem nut of multi-purpose siamese connections shall be made of cast copper alloy ZCuZn38 conforming to GB/T 1176, or other metal materials with mechanical properties and corrosion resistance not lower than those of cast copper alloy ZCuZn38.
5.2.5 The valve stem of multi-purpose siamese connections shall be made of lead brass HPb59-1 conforming to GB/T 4423, or other metal materials with mechanical properties and corrosion resistance not lower than those of HPb59-1.
5.3 Appearance quality
5.3.1 The surface of the body casting of the siamese connection shall be smooth. Both internal and external surfaces shall be spray-coated or otherwise treated against corrosion. The exposed upper part of the siamese connection shall be red in colour. The coating shall be uniform in colour and lustre, free from cracking, obvious scratches and impact damage.
5.3.2 The surface of copper alloy castings or stainless steel castings of the siamese connection shall be free from obvious sand holes, gas pores, shrinkage cavities, slag inclusions, cracks, cold shuts and other defects.
5.4 Threads
The basic dimensions and tolerances of pipe threads of the siamese connection shall comply with GB/T 7307. The tolerances of general purpose metric screw threads shall comply with the requirements of Class 7H for internal threads and Class 8g for external threads in GB/T 197. Threads shall be free from missing teeth and shall have a smooth surface.
5.5 Connection methods
5.5.1 When the siamese connection adopts a flanged connection, the flange connection dimensions and flange sealing face types shall comply with GB/T 9124.1 or GB/T 17241.1.
5.5.2 When the siamese connection adopts a grooved connection, the connection dimensions shall comply with GB 5135.11.
5.6 Handwheel
The handwheel type for multi-purpose siamese connections shall comply with JB/T 7273.3. The handwheel diameter shall comply with Table 1. The tolerances of its dimensions shall comply with Grade v in GB/T 1804-2000. The handwheel rim shall have permanent arrows and wording indicating the direction of opening and closing.
5.7 Lifting height
For multi-purpose siamese connections with a nominal size of DN100, the lifting height shall be greater than 30 mm. For multi-purpose siamese connections with a nominal size of DN150, the lifting height shall be greater than 35 mm.
5.8 Sealing performance
Under a water pressure equal to the rated working pressure, there shall be no leakage at any connection part of the siamese connection. The shut-off device, check valve, safety valve and residual water drain valve shall also be free from leakage.
5.9 Hydrostatic strength performance
Under a water pressure of 1.5 times the rated working pressure, all castings of the siamese connection shall be free from leakage and damage that affects normal use.
5.10 Valves
5.10.1 Each type of valve shall comply with the corresponding product standard.
5.10.2 For siamese connections with a rated working pressure of 1.6 MPa, the opening pressure of the safety valve shall be (1.78 ± 0.05) MPa; for siamese connections with a rated working pressure of 2.5 MPa, the opening pressure of the safety valve shall be (2.78 ± 0.08) MPa; for siamese connections with a rated working pressure of 4.0 MPa, the opening pressure of the safety valve shall be (4.44 ± 0.13) MPa. The opening/closing differential pressure of the safety valve shall not exceed 20%. For siamese connections with a nominal size of DN100, the nominal size of the safety valve shall not be less than DN20; for siamese connections with a nominal size of DN150, the nominal size of the safety valve shall not be less than DN32.
5.11 Fire fighting coupling
