Eight necessary technical factors for purchasing valves
General requirements, valve material, transmission box, valve operating mechanism, valve performance testing, valve internal and external anti-corrosion, valve packaging and transportation, valve factory instructions
1. General requirements
1.1valveThe specifications and categories shall meet the requirements of the pipeline design documents.
1.2 The model of the valve should indicate the numbering requirements of the national standard. If it is an enterprise standard, the relevant description of the model should be indicated.
1.3 The working pressure of the valve requires ≥ the working pressure of the pipeline. Under the premise of not affecting the price, the working pressure that the valve can bear should be greater than the actual working pressure of the pipeline; any side of the valve should be able to withstand 1.1 times the working pressure of the valve when it is closed value without leakage; when the valve is open, the valve body should be able to withstand the requirements of twice the working pressure of the valve.
1.4 For valve manufacturing standards, the national standard number of the basis should be stated. If it is an enterprise standard, the enterprise documents should be attached to the purchase contract.
2.1 The material of the valve body should be mainly ductile iron, and the grade and the actual physical and chemical test data of the cast iron should be indicated.
2.2 The valve stem material should be made of stainless steel valve stem (2CR13), and the large diameter valve should also be a valve stem embedded in stainless steel.
2.3 The nut material is cast aluminum brass or cast aluminum bronze, and its hardness and strength are greater than that of the valve stem.
2.4 The material of the valve stem bushing should have no hardness and strength greater than that of the valve stem, and it should not form electrochemical corrosion with the valve stem and valve body under water immersion.
2.5 Material of sealing surface ① There are different types of valves, different sealing methods and material requirements; ② For ordinary wedge gate valves, the material, fixing method, and grinding method of the copper ring should be explained; ③ Soft-sealed gate valves, the rubber lining material of the valve plate Physical, chemical and hygienic testing data; ④ Butterfly valves should indicate the material of the sealing surface on the valve body and the material of the sealing surface on the butterfly plate; their physical and chemical testing data, especially the hygienic requirements, anti-aging performance and wear resistance of rubber; Acrylic rubber and EPDM rubber, etc., it is strictly forbidden to mix reclaimed rubber.
2.6 Valve shaft packing ①Because the valves in the pipe network are usually opened and closed infrequently, the packing is required to be inactive for several years, the packing will not age, and the sealing effect will be maintained for a long time; ②The valve shaft packing should also withstand frequent opening and closing , the sealing effect is good; ③ In view of the above requirements, the valve shaft packing should not be replaced for life or more than ten years; ④ If the packing needs to be replaced, the valve design should consider the measures that can be replaced under the condition of water pressure.
3. Variable speed transmission box
3.1 The box body material and internal and external anti-corrosion requirements are consistent with the principle of the valve body.
3.2 The box should have sealing measures, and the box can withstand immersion in a water column of 3 meters after assembly.
3.3 For the opening and closing limit device on the box, the adjusting nut should be inside or outside the box, but special tools are required for operation.
3.4 The design of the transmission structure is reasonable. When opening and closing, it can only drive the valve shaft to rotate without causing it to move up and down.
3.5 The variable speed transmission box and the valve shaft seal cannot be connected into a leak-free whole, otherwise there should be reliable anti-leakage measures.
3.6 There is no debris in the box, and the gear meshing parts should be protected by grease.
4. The operating mechanism of the valve
4.1 The opening and closing direction of the valve operation should be closed clockwise.
4.2 Since the valves in the pipe network are often opened and closed manually, the number of opening and closing revolutions should not be too much, even large-diameter valves should also be within 200-600 revolutions.
4.3 In order to facilitate the opening and closing operation by one person, the maximum opening and closing torque should be 240N-m under the pressure of the plumber.
4.4 The opening and closing operation end of the valve should be a square tenon with standardized dimensions and face the ground so that people can directly operate it from the ground. Valves with discs are not suitable for underground pipe networks.
4.5 Display panel of valve opening and closing degree ①The scale line of valve opening and closing degree should be cast on the gearbox cover or on the shell of the display panel after the direction is changed, all facing the ground, and the scale line should be painted with fluorescent powder to show eye-catching; ② The material of the indicator needle can be made of stainless steel if the management is good, otherwise it is a painted steel plate, and do not use aluminum skin; ③ The indicator needle is eye-catching and fixed firmly. Once the opening and closing adjustment is accurate, it should be rivet locking.
4.6 If the valve is buried deep, and the distance between the operating mechanism and the display panel is ≥1.5m from the ground, there should be an extension rod facility, and it should be fixed firmly so that people can observe and operate from the ground. That is to say, the opening and closing operation of valves in the pipe network is not suitable for downhole operations.
5. Valve performance testing
5.1 When the valve is manufactured in batches of a certain specification, an authoritative organization should be entrusted to carry out the following performance testing: ①The opening and closing torque of the valve under the working pressure condition; ②Under the working pressure condition, the continuous opening and closing times that can ensure the valve is tightly closed; ③ Detection of the flow resistance coefficient of the valve under the condition of pipeline water delivery.
5.2 The valve should undergo the following tests before leaving the factory: ①When the valve is open, the valve body should withstand the internal pressure test of twice the working pressure of the valve; ②When the valve is closed, both sides should bear 1.1 times the working pressure of the valve , no leakage; but the metal-sealed butterfly valve, the leakage value is not greater than the relevant requirements.
6. Internal and external anti-corrosion of valves
6.1 The inside and outside of the valve body (including the variable speed transmission box) should first be shot blasted to remove sand and rust, and strive to electrostatically spray powdery non-toxic epoxy resin with a thickness of more than 0.3mm. When it is difficult to electrostatically spray non-toxic epoxy resin for extra-large valves, similar non-toxic epoxy paint should also be brushed and sprayed.
6.2 The interior of the valve body and all parts of the valve plate are required to be fully anti-corrosion. On the one hand, it will not rust when soaked in water, and no electrochemical corrosion will occur between the two metals; on the other hand, the surface is smooth to reduce the water resistance.
6.3 The hygienic requirements of the anti-corrosion epoxy resin or paint in the valve body should have the test report of the corresponding authority. The chemical and physical properties should also meet the relevant requirements.
7. Valve packaging and transportation
7.1 Both sides of the valve should be sealed with light blocking plates.
7.2 Medium and small caliber valves should be bundled with straw ropes and transported in containers.
7.3 Large-diameter valves are also packaged in simple wooden frame solid packaging to avoid damage during transportation.
8. The factory manual of the valve.
Valves are equipment, and the following relevant data should be indicated in the factory manual: valve specification; model; working pressure; manufacturing standard; valve body material; valve stem material; sealing material; valve shaft packing material; valve stem bushing material; internal and external anti-corrosion materials ;Operation starting direction; Number of revolutions; Opening and closing torque under working pressure; Manufacturer name; Date of manufacture; Factory serial number; , width and height control dimensions; valve flow resistance coefficient; effective opening and closing times; relevant data of valve factory inspection and precautions for installation and maintenance, etc.