As the proportion of plastic PVC valve piping in cold and hot water supply and industrial piping engineering applications continues to increase, the quality control of plastic valves in plastic PVC valve piping systems is becoming more and more important. Due to the advantages of light weight, corrosion resistance, non-adsorption of scale, plastic pipes can be integrated with plastic PVC valves and long service life, plastic PVC valve pipes are used in water supply (especially hot water and heating) and In the plastic piping system of other industrial fluids, its application advantages are incomparable with other valves.
At present, in the production and application of domestic plastic PVC valve pipelines, there is no reliable method to control it, resulting in uneven product quality of plastic PVC valve pipelines for water supply and other industrial fluids, and poor closing in engineering applications. And the leakage phenomenon is serious, forming a statement that plastic PVC valve pipes cannot be used, which affects the overall development of plastic pipe applications. my country's Fengquan plastic PVC valve pipeline national standard is in the process of formulation, and its product standards and method standards are formulated in accordance with international standards.
Internationally, the types of plastic PVC valve pipelines mainly include ball valves, butterfly valves, check valves, diaphragm valves, gate valves and globe valves. The main structural forms are two-way, three-way and multi-way valves. The raw materials are mainly ABS, PVC-U, PVC-C, PB, PE, PP and PVDF etc.
In the international standards for plastic PVC valve and piping products, the first is to require the raw materials used in the production of valves. The manufacturer of the raw materials must have a creep failure curve that meets the standards of plastic piping products; at the same time, the sealing test and valve body test of plastic valves are required. , The long-term performance test, fatigue strength test and operating torque of the overall valve have been specified, and the design service life requirements of the plastic PVC valve pipeline used for industrial transportation of fluids are given.
Plastic PVC valve pipe material classification description:
CPVC fittings has good tensile and compressive strength, but its flexibility is not as good as other plastic pipes, and it has excellent corrosion resistance. The price is the cheapest among all kinds of plastic pipes, but it is more brittle at low temperature. The connection method is bonding and socket. Rubber ring connection and flange thread connection are mainly used for water supply and drainage, irrigation, gas supply, exhaust pipes, wire conduits, rainwater pipes, industrial anticorrosive pipes, etc. in residence, industry, mining, and agriculture.
CPVC features excellent heat resistance, heat distortion temperature of 100 ℃, excellent chemical resistance, bonding method, flange thread connection is mainly used for hot water pipes.
PE pipe features light weight, good resistance, good low temperature resistance, non-toxic, relatively cheap, high impact strength, but low compression and tensile strength. Connection method: hot melt welding and flange thread connection are mainly used for drinking water Pipes, rainwater pipes, gas pipes, industrial corrosion-resistant pipes.
PP pipe features good corrosion resistance, good strength, high surface hardness, surface finish, and certain high temperature resistance. Connection method hot melt welding, flange thread connection is mainly used for chemical sewage, sea water, oil and irrigation The pipes are used for indoor concrete floors as heating pipes for heating systems.
ABS pipe features excellent corrosion resistance, light weight, higher heat resistance than PE and PVC, but the price is more expensive. Connection method: Bonding and flange thread connection are mainly used for sanitary ware drain pipes, beggar pipes, sewage pipes, underground cable pipes, and high-corrosion industrial pipelines.
The strength of PB pipe is between PE and PP, and the flexibility is between LDPE (LDPE: low-density polyethylene) and HDPE (HDPE: high-density polyethylene). Its outstanding feature is its creep resistance (cold deformation). Winding and continuous, temperature resistance, and excellent chemical function. Connection method: hot melt welding, flange thread connection is mainly used for water supply pipes, cold and hot water pipes, gas pipes, underground high-level pipelines, GRP pipes, excellent corrosion resistance and light weight , High strength, good portability and good function. Connection method: Socket apron connection and flange connection are widely used in petrochemical pipelines and large-diameter water supply and drainage pipelines.
Description of the method for identifying the size of the pipe diameter of the plastic PVC valve:
The nominal size and nominal pressure marking method of plastic pipes and plastic PVC valves are inconsistent. The nominal size of Fengquan plastic pipes is expressed by the nominal outer diameter dn, and the nominal size of plastic PVC valves is expressed by the nominal diameter DN; plastic pipes used for cold and hot water are not allowed to be marked with nominal pressure PN, and the pipe series S is marked according to the use condition level Select the use pressure, and Fengquan plastic PVC valves are marked with the nominal pressure PN, and the temperature grade coefficient fr is used to select the use temperature.
The operating torque requirements in EN 12570:2000 are too low, because the greater the torque of the valve, the greater the wear of the valve seat and the shorter the service life. For the plastic PVC valves of domestic manufacturers that have done torque tests, the torque with a handle size of less than 100 is only about 3N·m, which is equivalent to an operating force of only about 30N, which is far lower than the standard requirement of 250N. Whether it is possible to increase the index, it is also necessary to increase the verification of products of different manufacturers.
The standard does not specify the size of the torque of different specifications of plastic PVC valve pipes. Only the requirements for the length of the handle (or the diameter of the handwheel) and the force are given. The quality of the torque of the valve product cannot be guaranteed, because the manufacturer can extend the length of the handle ( (Or handwheel diameter) method to make non-conforming products into qualified products.
The design stress 6S of PP-R is 5MPa, and the design stress 6Ss of some raw materials in the world has been increased to 6.3MPa or 8MPa for plastic PVC valve pipes. The choice of design strength is somewhat conservative compared to other raw material varieties.
The minimum diameter of the reduced diameter valve does not give quantitative requirements for the minimum size of different specifications, only the manufacturer is required to indicate it. This makes the products of some manufacturers whose valve diameters are too much smaller than those of the same specification, but it will increase the local resistance of the piping system.
The standard gives the design service life requirements of plastic valves used in industrial transport fluids, but does not give the design service life time for the domestic water supply system. As long as the selection of raw materials and product control are carried out in accordance with international standards, plastic PVC valve pipes can fully meet the requirements of use. At the same time, there are also some inappropriate points in the international standards, and we need to pay attention to its development trends.
