By introducing the requirements for raw materials, design requirements, manufacturing requirements, performance requirements, test methods, system application requirements and the relationship between the use pressure and temperature in the standards of international plastic valve products and test methods, we can understand the basic quality control requirements for plastic valves, such as sealing test, torque test and fatigue strength test.

Abstract

The regulations on valve seat sealing test, valve body sealing test, valve body strength test, valve long-term test, fatigue strength test and operating torque required for the performance requirements of plastic valve products are summarized in the form of a table. Through the discussion of several problems in international standards, the producers and users of plastic valves have attracted attention.

Keywords

Plastic valve service life sealing test fatigue strength test test conditions

With the increasing proportion of plastic pipelines in the application of cold and hot water supply and industrial pipeline engineering, the quality control of plastic valves in plastic pipeline systems has become increasingly important.

Due to the advantages of plastic valves such as light weight, corrosion resistance, no adsorption of scale, integrated connection with plastic pipes and long service life, the application advantages of plastic valves in plastic pipe systems for water supply (especially hot water and heating) and other industrial fluids are unmatched by other valves. At present, there is no reliable method to control the production and application of plastic valves in China, resulting in uneven quality of plastic valves for water supply and other industrial fluids, lax closure and serious leakage in engineering applications, forming a saying that plastic valves cannot be used, affecting the overall development of plastic pipe applications. The national standard for plastic valves in China is being formulated, and its product standards and method standards are formulated according to international standards.

The types of plastic valves in the world mainly include ball valves, butterfly valves, check valves, diaphragm valves, gate valves and stop valves, etc. The main structural forms are two-way, three-way and multi-way valves, and the main raw materials are ABS, PVC-U, PVC-C, PB, PE, PP and PVDF.

In the international standards for plastic valve products, the first requirement is for the raw materials used in the production of valves. The raw material manufacturers must have creep failure curves that meet the standards for plastic pipe products. At the same time, the sealing test, valve body test, long-term performance test of the overall valve, fatigue strength test and operating torque of plastic valves are regulated, and the design service life of plastic valves used for industrial fluid transportation is 25 years.

Technical requirements

1.1 Raw material requirements

The materials of the valve body, bonnet and valve cover should be selected in accordance with ISO 15493:2003 "Industrial Plastic Piping Systems - ABS, PVC-U and PVC-C - Pipe and Fittings System Specifications - Part 1: Metric Series" and ISO 15494:2003 "Industrial Plastic Piping Systems - PB, PE and PP - Pipe and Fittings System Specifications - Part 1: Metric Series".

1.2 Design requirements

a) If the valve has only one pressure-bearing direction, it should be marked with an arrow on the outside of the valve body. Symmetrically designed valves should be suitable for bidirectional flow and isolation of fluids.

b) The sealing component is driven by the valve stem to open and close the valve. It should be positioned by friction or actuator at the end or any intermediate position. The fluid pressure cannot change its position.

c) According to EN736-3, the minimum through hole in the valve cavity should meet the following two points:

- For any aperture on the valve through which the medium flows, it should not be less than 90% of the valve DN value;

- For valves that need to reduce the aperture of the medium flow in the structure, the manufacturer should indicate the actual minimum through hole.

d) The seal between the valve stem and the valve body should comply with EN736-3.

e) In terms of valve wear resistance, the design of the valve should take into account the service life of the wear parts, or the manufacturer should indicate the recommendation to replace the entire valve in the operating instructions.

f) The applicable flow rate of all valve operating devices should reach 3m/s.

g) When viewed from the top of the valve, the valve handle or handwheel should close the valve in a clockwise direction.

1.3 Manufacturing requirements

a) The performance of the purchased raw materials should be consistent with the instructions of the raw material manufacturer and meet the requirements of the product standards.

b) The raw material code, diameter DN, and nominal pressure PN used should be marked on the valve body.

c) The valve body should be marked with the manufacturer's factory name or trademark.

d) The valve body should be marked with the production date or code.

e) The valve body should be marked with the manufacturer's codes for different production locations.

1.4 Short-term performance requirements

Short-term performance is a factory inspection item in the product standard. It mainly involves the valve seat sealing test and the valve body sealing test. It is used to check the sealing performance of plastic valves. It is required that plastic valves should not have internal leakage (valve seat leakage) or external leakage (valve body leakage).

The valve seat sealing test verifies the performance of the valve isolation pipeline system; the valve body sealing test verifies the leakage of the valve stem seal and the valve connection end seals.

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