Abstract: By introducing the requirements of raw materials, design requirements, manufacturing requirements, performance requirements, test methods, system application requirements and the relationship between the use of pressure and temperature in the international standards for plastic valve products and test methods, we can understand the requirements for plastic valves Seal test, torque test and fatigue strength test and other basic quality control requirements. Form the table summarizes the performance requirements of the plastic valve valve seat sealing test, the body seal test, body strength test, the valve long-term test, fatigue test and the provisions of operating torque. Through the discussion of several problems in international standards, producers and users of plastic valves have drawn much attention. Keywords: plastic valve life seal test fatigue strength test test conditions With the plastic pipe in the hot and cold water supply and the proportion of industrial pipe engineering applications continue to improve, plastic pipe system plastic valve quality control is more and more appear to be more and more important. Due to the plastic valve has the advantages of light weight, corrosion resistance, non-adsorption scale, integration with the plastic pipe and long service life, etc., plastic valves in the water supply (especially hot water and heating) and other industrial plastics Pipeline system, the advantages of its application is that other valves can not be compared. Currently in the domestic production and application of plastic valves, there is no reliable method of its control, resulting in water supply and industrial use of other fluids plastic valve product quality is uneven, resulting in the closure of engineering applications and serious leakage phenomenon, The formation of a plastic valve can not use the remarks, affecting the overall development of plastic pipe applications. China's national standard plastic valve is being developed in the process, the product standards and method standards are based on international standards. The main types of plastic valves in the world are ball valves, butterfly valves, check valves, diaphragm valves, gate valves and globe valves. The main types of structure are two-way, three-way and multi-way valves. C, PB, PE, PP and PVDF and so on. In the international standards for plastic valve products, the first is the production of raw materials used in the valve requirements, the raw materials of the manufacturer must have a plastic pipe products meet the creep damage curve [1]; the same time, the plastic valve seal test, the valve body Tests, long-term performance tests of integral valves, fatigue strength tests and operating torques are all provided. The design service life of plastic valves for industrial fluid transfer is 25 years [2]. 1 The main technical requirements of international standards 1.1 Material requirements Valve body, bonnet and bonnet materials should be used in line with 1.2 design requirements a) If the valve is only one direction of pressure, the valve body should be marked with the arrow, the symmetrical design of the valve Should be suitable for two-way fluid flow and isolation. b) The sealing member is driven by the valve stem to open and close the valve. It should be positioned at the end point or in the middle by friction or actuator, and the fluid pressure can not change its position. c) According to EN736-3, the valve cavity minimum through-hole shall comply with the following two points: - for any aperture through which the medium is to be circulated through the valve, not less than 90% of the valve DN value; - for structurally reduced media flow Aperture valves, the manufacturer should explain the actual minimum through-hole. d) The seal between stem and body shall 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 wearing parts or the manufacturer should indicate in the operating instructions that the entire valve be replaced. f) The flow rate applicable to all valve operators shall be 3 m / s. g) 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 purchased raw materials should be consistent with the instructions of the manufacturer of raw materials, and meet the product standards. b) The body should be marked on the raw material code, diameter DN, nominal pressure PN. c) Body should be marked with the manufacturer's name or trademark. d) Body should be marked with the date of manufacture or code. e) The valve body shall be marked with the code of the manufacturer's different manufacturing locations. 1.4 Short-term performance requirements Short-term performance in the product standard is part of the factory inspection items, mainly to do the seat seal test and body sealing test for checking the sealing performance of plastic valves require plastic valves that can not have internal leakage (valve Seat leakage) phenomenon, can not have external leakage (body leakage) phenomenon. Seat seal test is to verify the performance of the valve isolation pipe system; the body of the seal test is to verify the valve stem seals and valves at the junction of the seal leak. Test conditions in Table 1. Table 1 Seat and valve test conditions [3] Tab.1Conditionforseatandpackingtests Test minimum test time / s Test pressure / MPa Temperature / ℃ Test medium · Internal test medium · External seat test (valve closed) 1) 60 0.052) 20 ± 2 Air water 5) 1.1 × PN3) 20 ± 2 Water 4) Air tightness test (valve open) 6) 1.5 × PN3) 20 ± 2 Water 4) Air NOTE 1) Operate the valve according to the torque requirements of the product; 2 ) The minimum test pressure 0.05MPa; 3) The maximum test pressure (PN +0.5) MPa; 4) or the internal air is water pressure is (0.6 ± 0.1) MPa; 15s, DN ≥ 250: the minimum test time 30s; 6) valve nominal size DN ≤ 50: the minimum test time 15s, DN ≥ 65: the minimum test time 30s. Test Method: According to ISO1167 "Thermoplastics Tubing Fluid Resistance Pressure Test Method" requirement. Valve sealing test should be done in the full state; do the valve body sealing test should make the valve in the fully open position or half-open position (such as ball valve), half-open should enable the fluid into the stem seal position. For one-way sealed valves, only one direction of the seat seal test; and two-way sealed valve, the two directions of the seat seal test needs to be done. Required to drain the valve test sample air, gradually increase the test pressure, 30s to achieve the required pressure. It should be noted that the test device during the test valve can not generate additional stress. If air is used as the test medium, safety measures against compressed gas must be taken. 1.5 Long-term performance requirements 1.5.1 Body test and overall valve long-term performance test belong to the type test items in the product standard, body test is used to verify the strength of the valve body, the overall valve long-term performance test is used to verify the overall reliability of plastic valve design Sex. Valve test conditions in Table 2. Material Minimum test time / h Test pressure Pt1) / MPa Design stress / бs1) Temperature / ℃ Test medium · Internal test medium · External PE100 1.55 × PN 0.69 × PN 0.62 × PN 8 20 ± 2 80 ± 2 80 ± 2 Water Water Water Water Water PE80 1.59 × PN 0.73 × PN 0.63 × PN 6.3 20 ± 2 80 ± 2 80 ± 2 Water Water Water Water Water Water PP-H, PP-R-GR PP-B PP- R 1 1000 4.2 × PN 0.7 × PN 5 20 ± 2 95 ± 2 Water Water Water or air 1 1000 3.2 × PN 0.52 × PN 5 20 ± 2 95 ± 2 Water Water Water or air 1 1000 3.2 × PN 0.7 × PN 5 20 ± 2 95 ± 2 Water Water Water or air PVC-U PVC-UH dn <160 dn ≥ 160 1 1000 4.2 × PN 3.2 × PN 10 20 ± 2 20 ± 2 Water Water Water 1 1000 4.2 × PN 3.2 × PN 10 20 ± 2 20 ± 2 Water Water Water 1 1000 3.36 × PN 2.56 × PN 12.5 20 ± 2 20 ± 2 Water Water Water PVDF 200 0.72 × PN 16 95 ± 2 Water or air Note 1) Pt pressure is calculated as follows: Pt = PN × бt / бs where: бt - test stress; бs - design stress. Table 2 valve test conditions [3] The overall valve long-term performance test conditions in Table 3. Table 3 conditions for long-term performance test [3] Tab.3Conditionsforlong-termbehaviourtestest Materials Minimum test time / h Test pressure Pt / MPa Temperature / ℃ Test medium · Internal test medium · External PE100, PE80 1000 1.5 × PN 20 ± 2 Water PP -HPP-B, PP-R, PP-R-GR 2.24 × PN1.6 × PN 20 ± 220 ± 2 Water Water Water PVC-U, PVC-UH 1000 1.3 × PN 40 ± 2 Water PVDF 1000 1.45 × PN 20 ± 2 Water Water NOTE: For diaphragm valves, the test pressure for valves of materials other than PVC-U and PVC-UH (1.3 × PN) and PVDF (1.45 × PN) is 1.5 × PN. Test Method: According to ISO1167 "Thermoplastics Tubing Fluid Resistance Pressure Test Method" requirement. Valve body test and the overall performance of the valve long-term performance test required to drain the air in the valve sample, and gradually increase the test pressure, 30s to achieve the required pressure, the test device during the test device can not generate additional stress on the valve. 1.5.2 Body test and the overall valve long-term performance test is the valve body and valve according to ISO12092 "without plasticized PVC (PVC-U), chlorinated polyvinyl chloride (PVC-C), acrylonitrile-butadiene (ABS), Acrylonitrile - Styrene - Acrylate (ASA) Pipe, Fittings and Valves - Internal Pressure Resistance - Test Method ". 1.5.3 In the valve body test and the overall valve long-term performance test during the test, the sample did not leak or rupture, then determine the test pass. Sample leak or rupture before the end of the test, then determine the test failed. If there is a problem at the junction, the test is judged to be invalid and the sample test needs to be re-taken. 1.6 System Requirements 1.6.1 Fatigue Strength Test [4] The valve shall be opened and closed in the following state fatigue strength test: a) test medium is water, the pressure at the valve inlet pressure PN and the temperature of (20 ± 3) ℃ conditions; b) the valve is fully open, so that the water flow rate of (1 ± 0.2) m / s; c) the valve is closed, the output pressure is atmospheric pressure; d) then the valve fully open, Of the flow rate of (1 ± 0.2) m / s; e) no less than 5000 cycles. Test methods should be consistent with the standard requirements, fatigue strength test after all functional parts should be kept intact, but also to meet the short-term performance of the sealing test requirements. 1.6.2 Torque test [5] The manual valve should be operated under the condition of nominal pressure and room temperature and adjusted according to the standard state, then the operating torque test shall be carried out and the maximum permissible operating torque value of the valve fully open or fully closed shall be given. This value by the part of the machining accuracy and assembly fluctuations. 1.6.3 Operation Permissible Force Requirements The full-opening and full-closing forces of the plastic valve handle or handwheel shall not exceed the F-value given in Table 4. Table 4 Operating Force [6] Tab.4Manualforce L F Fs Note : L handle or hand wheel operating lever length in mm; F ​​operating force in Newtons (N); FS maximum operating force in Newtons (N). 1.6.4 Connection dimensions a) End face - End face dimensions The flange face end face - end face dimensions of the system connection valves shall be selected from the following standards: - Flanges for PN design see EN 558-1; Flanges for CLASS design see EN 558-2. Other types of connecting ends shall be determined by the manufacturer. b) Valve connection size The connection dimension of the flange connection valve shall meet the following standards: - For the flange designed for PN, see EN1092-1; For the flange designed for -Class, see the thread size of the valve connection end shall be in accordance with ISO7-1 or ISO228-1 . 1.6.5 plastic valve and pipe system connection way to the butt welding connection: the outer diameter of the valve connecting parts and pipe outer diameter equal to the end face of the valve connecting parts and pipe end face welding; socket adhesive connection: the valve connecting parts For the socket form, and pipe fittings for bonding connection; fused socket connection: the valve connecting parts for the inner diameter laying electric wire socket form, and the pipe fused connection; socket hot melt connection: valve connection parts for the socket form , And the pipe hot melt socket connection; socket adhesive connection: the valve connecting parts for the socket form, and the pipe for bonding socket connection; socket rubber seal connection: the valve connecting parts for the inner rubber seal Socket type, and the pipe socket connection; flange connection: the valve connecting parts in the form of flanges, and the pipe flange connection; screw connection: the valve connection parts for the thread form, and the pipe or pipe thread on Connected; live connection: the valve connecting parts of the live form, with the pipe or pipe connections. A valve can have different connections at the same time. 1.7 The relationship between the use of pressure and temperature As the use of temperature, the life of plastic valves to be shortened. In order to maintain the same life, you need to reduce the use of pressure. Table 5 shows the temperature coefficient of the body material fr. TABLE 5 Grade factor for service life of 25 years fr [2] Tab. 5 Minimum Value forratingfactorfrforalifetimeup25years Temperature / ° C ABS PE80 PP-H PVC-C PVC-U PVDF -40 1.0 1.0 - - - a -30 1.0 1.0 - - - a -20 1.0 1.0 - - - 1.0 -10 1.0 1.0 - - - 1.0 05 1.01.0 1.01.0 -1.0 - - 1.0 1.0 10 1.0 1.0 1.0 1.0 1.0 1.0 20 1.0 1.0 1.0 1.0 1.0 1.0 25 1.0 1.0 1.0 1.0 1.0 1.0 30 0.80 0.76 0.85 0.85 0.80 0.90 40 0.60 0.53 0.70 0.65 0.60 0.80 50 0.40 0.35 0.55 0.50 0.35 0.71 60 0.20 0.24 0.40 0.35 0.15 0.63 70 - - 0.27 0.25 - 0.54 80 - - 0.15 0.15 - 0.47 90 - - 0.08 a - 0.36 100 - - a - - 0.25 110 - - - - - 0.17 120 - - - - - 0.12 130 - - - - - a 140 - - - - - a Note: These rating factors fr are not consistent with the rest of the pipe and fittings . a: This grade factor should be given by the manufacturer. 1.8 Nominal pressure PN calculation: PN = бs / S where бs-design stress in MPa S-pipe connection with the valve pipe series PN-nominal pressure in MPa 2 2.1 Discussion of plastic pipe and plastic valve nominal size, Nominal pressure marked inconsistent. Plastic pipe nominal size nominal diameter dn said the nominal size of the plastic valve nominal diameter DN said; for hot and cold water plastic pipe nominal pressure PN is not allowed, marking pipe series S according to the level of use conditions select the use of pressure , While the plastic valve is marked nominal pressure PN, with the temperature level coefficient fr to select the use of temperature. Here need attention. 2.2 In 2.3, the standard does not specify the size of different specifications of the valve torque, only the length of the handle (or hand wheel diameter) and force requirements, can not guarantee the torque quality of valve products, because the manufacturer can lengthen the handle length Or hand wheel diameter) to make the nonconforming product into a conforming product. 2.4 Table 2 PP-R design stress бs 5MPa, and now the international design stress of some raw material бs has been increased to 6.3MPa or 8MPa, the choice of design strength relative to other species in terms of some conservative. 2.5 The minimum diameter of the valve does not give the minimum size of the different specifications of the quantitative requirements, only the manufacturer indicated. This makes some manufacturers reduce the valve size of the product relative to the same size products seem compact, but will result in increased partial resistance of the piping system. 2.6 The standard specifies the 25-year service life of plastic valves for the industrial transfer of fluids and does not give the design life-time for domestic water supply systems. 3 Conclusion As long as the choice of raw materials and product control are in accordance with international standards, plastic valves can fully meet the requirements of the use of plastic pipe. At the same time there are also some inappropriate international standards, the need to pay attention to its development.
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