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What is a plastic valve?

2022-07-22 15:39:53

What is a plastic valve?

Plastic valve is a general term for the control device for the on, off, and flow regulation of the operable medium in the plastic piping system.

Because plastic valves have the advantages of lightweight, corrosion resistance, non-adsorption of water ditch, integrated connection with plastic pipes, and long service life, plastic valves are widely used in plastic pipes for water supply (especially hot water and heating) and other industrial fluids. In the road system, the advantages of the application are unmatched by other valves.

The types of plastic valves used in chemical pipelines mainly include plastic ball valves, plastic butterfly valves, plastic check valves, plastic diaphragm valves, plastic gate valves, and plastic globe valves. The structural forms mainly include two-way, three-way, and multi-way valves. The main raw materials of the valve mainly include ABS, PVC-U, PVC-C, PB, PE, PP, PVDF, and PPO.

In the international standards for plastic valve products, the first is to put forward requirements for the raw materials used in the production of plastic valves. The original manufacturer must issue a creep failure curve and grading certificate that conforms to the standard of plastic pipe products; The valve sealing test, valve body test, long-term performance test of the whole valve, fatigue strength test, and operating torque is specified, and the design service life of plastic valves for conveying industrial water is given for 25 years.

minimum wall thickness of the pipe with the same calculated diameter: the minimum flow section diameter of the plastic valve is generally not less than 90% of the nominal size. If it is less than 90% of the nominal size, the value of the actual minimum flow section diameter of the valve should be indicated.

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For valve materials under fluid conditions

The selection of materials directly affects the safe operation of the pipeline, so the selection of materials should be careful, fully meet the requirements of the design conditions ( pressure, temperature, medium properties, environment, etc.), and leave a margin.

 

Factors to consider:

  1. the degree of reduction in the melting point, softening temperature, and material strength of plastic valve materials under exposure conditions.
  2. The susceptibility of plastic valves to brittle fracture or damage due to thermal shock when encountering fire or taking fire fighting measures, and the degree of harm caused by rupture of plastic valves due to damage.
  3. In the event of a fire, the ability of a thermal insulation material to prevent damage to the pipeline (eg, stability, fire resistance, and ability to maintain its original position in a fire).
  4. The susceptibility of plastic valve materials to crevice corrosion under grommets, threaded joints, socket weld joints, and other stagnant closed areas.
  5. Compatibility of the lubricant or sealant used on the thread with the fluid service.
  6. Compatibility of gaskets, seals and fluid service.
  7. Compatibility of adhesives, solvents, etc. for pipe, fittings and plastic valve connections with fluid service conditions.
  8. Because in the operation of the plastic valve, it is easy to generate harmful static electricity. It should be considered that when conveying non-conductive fluid media, grounding devices should be installed on the metal components of plastic valves.
  9. When the conveyed material is a strong oxidizing medium (such as oxygen, fluorine), the designer should pay more attention to the adaptability of the pipeline material, adhesive, sealing packing, etc. to the fluid conditions.

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special requirements

  1. PVC – U and PVC – C materials have poor wear resistance and are not suitable for conveying gas-solid two-phase fluids.
  2. PVC – U and PVC – C valves should not be used for compressed air or other compressed gas service.

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