Technical Requirements for Purchasing Valves
Specifications and categories of valves
1. The valve's model should be marked based on requirements of the national standard. If it is a corporate standard, the relevant description of the model should be indicated.
2. The working pressure of the valve is required to be greater than or equal to that of the pipeline. Under the premise of not affecting the price, the working pressure that the valve can withstand 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 the valve is closed and there should be no leakage. When the valve is open, the valve body should be able to withstand twice the working pressure of the valve.
3. For the manufacturing standard of the valve, the national standard number on which it is based should be stated. If it is a corporate standard, the purchase contract should be provided with corporate documents.
The selection of the material for the valve
1. Materials for valves: As gray cast iron pipes are gradually not recommended, the valve body's material should be mainly ductile iron. The grades and actual physical and chemical testing data of the castings should be indicated.
2. Materials for stems: Try to use stainless steel (20Cr13) for the stem as much as possible, and valves with large diameters should also adopt stainless steel embedded stems.
3. Materials for nuts: Cast aluminum brass or cast aluminum bronze should be adopted, and its hardness and strength should be greater than the valve stem.
4. Materials for valve stem bushings: They should have a hardness and strength not greater than that of the valve stem, and will not form electrochemical corrosion with the valve stem and valve body under water immersion.
5. Materials for sealing surfaces
① There are different requirements on sealing methods and materials for different types of valves.
② For ordinary wedge gate valves, their materials, fixing methods and grinding methods of the copper ring shall be explained.
③ For soft sealed gate valves, there should be physical, chemical and hygienic testing data for valve plate's lining materials.
④ The sealing surface material on the valve body and butterfly plate should be marked for butterfly valves. Their physical and chemical test data, especially the hygienic requirements, anti-aging performance, and wear resistance of rubber should be provided. Usually, use nitrile rubber and EPDM. It is strictly forbidden to mix with reclaimed rubber.
6. The packing of the valve shaft
① Since the valves in the pipeline are usually opened and closed infrequently, the packing is required not to age after being inactive for several years, and the sealing effect is maintained for a long time.
② The valve shaft packing should also have a good sealing effect when it is subjected to frequent opening and closing.
③ Given the above requirements, the valve shaft packing shall not be replaced for all the service life or more than ten years.
④ If the packing needs to be replaced, the valve design should consider measures that can be replaced under water pressure.
Variable speed transmission boxes
1. The material of the box body and the internal and external anti-corrosion requirements are consistent with that of the valve body.
2. There should be sealing measures for the box body, and the box body can withstand a height of 3 meters of water column immersion after assembly.
3. For the opening and closing limit device on the box body, the adjusting nut should be inside the box body.
4. The design of the transmission structure is reasonable. It can only drive the valve shaft to rotate when opening and closing, and does not make it move up and down. The transmission parts fit properly and do not cause separation and slippage when opening and closing with loads.
5. The seal of the variable speed transmission box and the valve shaft cannot be connected into a whole without leakages.
6. There is no debris in the box, and the occlusion of the gear part should be protected by grease.
The operating mechanism of the valve
1. The opening and closing direction of the valve should always be closed clockwise.
2. Since the valves in the pipeline are often opened and closed manually, the turning number of opening and closing should not be too many. For valves with large diameters, the turning number should be within 200-600.
3. In order to facilitate the opening and closing by one person, the maximum opening and closing torque should be 240N.m under the pipeline's working pressure condition.
4. The opening and closing 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 handwheels are not suitable for underground pipelines.
5. The display panel of the opening and closing degree of the valve
① The scale line of the valve's opening and closing degree should be marked on the cover of the gearbox or the shell of the display panel after changing the direction, facing the ground, and the scale line should be painted with fluorescent powder to be noticeable.
② The material of the indicator disc needle can be made of stainless steel plate under good management. Otherwise, painted steel plates should be used. Do not use aluminum plates.
③ The indicator disc needle is eye-catching and fixed firmly. Once the opening and closing adjustment is accurate, it should be fixed with rivets.
6. If the valve is buried deeply, and the distance between the operating mechanism and display panel is greater than and equal to 15 m from the ground, an extension rod should be provided and firmly fixed so that people can observe and operate from the ground. In other words, the opening and closing of valves in the pipeline should not be underground.
The performance testing of the valve
1. When the valve is manufactured in batches with a certain specification, an authoritative organization should be entrusted to carry out the following performance tests:
① The opening and closing torque of the valve under working pressure
② Under working pressure conditions, the number of continuous opening and closing of the valve for closing the valve well should be guaranteed.
③ The detection of the flow resistance coefficient of the valve under the condition of water delivery in the pipeline
2. The following tests should be performed for valves before leaving the factory:
① When the valve is open, the valve body should withstand the internal pressure test that is twice the valve's working pressure.
② When the valve is closed, both sides of the valve bear 11 times the valve's working pressure value, and there is no leakage. However, the leakage value of the metal-seated butterfly valve is not greater than the relevant requirements.
Internal and external corrosion protection of the valve
1. The inside and outside of the valve body including the variable speed transmission box should be shot blasted to clean the sand and rust, and use electrostatic spray the powdery non-toxic epoxy resin with a thickness from 0 to 3 mm. When it is difficult to electrostatically spray non-toxic epoxy resin for valves with extra-large sizes, similar non-toxic epoxy paint should be brushed or sprayed.
2. The inside of the valve body and the various parts of the valve plate require comprehensive anti-corrosion. On the one hand, the valve will not rust when it is immersed in water, and there will be no electrochemical corrosion between the two metals; on the other hand, the surface should be smooth to reduce the water resistance.
3. The sanitary requirements of the anticorrosive epoxy resin or paint in the valve body shall have the inspection report of the corresponding authority. The chemical and physical properties should also meet the relevant requirements.
The packaging and transportation of the valve
1. Lightweight blocking plates should be installed on both sides of the valve for sealing.
2. Valves with medium and small diameters should be bundled with straw ropes and transported in containers.
3. Valves with large diameters should be packaged with simple wooden boxes to avoid damage during transportation.
Checking the factory instructions of the valve
The valve is a device. The following relevant data should be indicated in the factory manual: valve specifications, models, working pressure, manufacturing standards, materials of valve bodies, valve stems, sealing, valve shaft packing and valve stem bushing, internal and external anti-corrosion materials, operating directions, turning numbers, opening and closing torque under working pressure conditions, names of manufacturers, dates of manufacture, manufacturing numbers, weights, effective opening and closing times, flow resistance coefficients of valves, relevant inspection data of valve factories and points for attention for installation and maintenance, etc.
1. The valve's model should be marked based on requirements of the national standard. If it is a corporate standard, the relevant description of the model should be indicated.
2. The working pressure of the valve is required to be greater than or equal to that of the pipeline. Under the premise of not affecting the price, the working pressure that the valve can withstand 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 the valve is closed and there should be no leakage. When the valve is open, the valve body should be able to withstand twice the working pressure of the valve.
3. For the manufacturing standard of the valve, the national standard number on which it is based should be stated. If it is a corporate standard, the purchase contract should be provided with corporate documents.
The selection of the material for the valve
1. Materials for valves: As gray cast iron pipes are gradually not recommended, the valve body's material should be mainly ductile iron. The grades and actual physical and chemical testing data of the castings should be indicated.
2. Materials for stems: Try to use stainless steel (20Cr13) for the stem as much as possible, and valves with large diameters should also adopt stainless steel embedded stems.
3. Materials for nuts: Cast aluminum brass or cast aluminum bronze should be adopted, and its hardness and strength should be greater than the valve stem.
4. Materials for valve stem bushings: They should have a hardness and strength not greater than that of the valve stem, and will not form electrochemical corrosion with the valve stem and valve body under water immersion.
5. Materials for sealing surfaces
① There are different requirements on sealing methods and materials for different types of valves.
② For ordinary wedge gate valves, their materials, fixing methods and grinding methods of the copper ring shall be explained.
③ For soft sealed gate valves, there should be physical, chemical and hygienic testing data for valve plate's lining materials.
④ The sealing surface material on the valve body and butterfly plate should be marked for butterfly valves. Their physical and chemical test data, especially the hygienic requirements, anti-aging performance, and wear resistance of rubber should be provided. Usually, use nitrile rubber and EPDM. It is strictly forbidden to mix with reclaimed rubber.
6. The packing of the valve shaft
① Since the valves in the pipeline are usually opened and closed infrequently, the packing is required not to age after being inactive for several years, and the sealing effect is maintained for a long time.
② The valve shaft packing should also have a good sealing effect when it is subjected to frequent opening and closing.
③ Given the above requirements, the valve shaft packing shall not be replaced for all the service life or more than ten years.
④ If the packing needs to be replaced, the valve design should consider measures that can be replaced under water pressure.
Variable speed transmission boxes
1. The material of the box body and the internal and external anti-corrosion requirements are consistent with that of the valve body.
2. There should be sealing measures for the box body, and the box body can withstand a height of 3 meters of water column immersion after assembly.
3. For the opening and closing limit device on the box body, the adjusting nut should be inside the box body.
4. The design of the transmission structure is reasonable. It can only drive the valve shaft to rotate when opening and closing, and does not make it move up and down. The transmission parts fit properly and do not cause separation and slippage when opening and closing with loads.
5. The seal of the variable speed transmission box and the valve shaft cannot be connected into a whole without leakages.
6. There is no debris in the box, and the occlusion of the gear part should be protected by grease.
The operating mechanism of the valve
1. The opening and closing direction of the valve should always be closed clockwise.
2. Since the valves in the pipeline are often opened and closed manually, the turning number of opening and closing should not be too many. For valves with large diameters, the turning number should be within 200-600.
3. In order to facilitate the opening and closing by one person, the maximum opening and closing torque should be 240N.m under the pipeline's working pressure condition.
4. The opening and closing 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 handwheels are not suitable for underground pipelines.
5. The display panel of the opening and closing degree of the valve
① The scale line of the valve's opening and closing degree should be marked on the cover of the gearbox or the shell of the display panel after changing the direction, facing the ground, and the scale line should be painted with fluorescent powder to be noticeable.
② The material of the indicator disc needle can be made of stainless steel plate under good management. Otherwise, painted steel plates should be used. Do not use aluminum plates.
③ The indicator disc needle is eye-catching and fixed firmly. Once the opening and closing adjustment is accurate, it should be fixed with rivets.
6. If the valve is buried deeply, and the distance between the operating mechanism and display panel is greater than and equal to 15 m from the ground, an extension rod should be provided and firmly fixed so that people can observe and operate from the ground. In other words, the opening and closing of valves in the pipeline should not be underground.
The performance testing of the valve
1. When the valve is manufactured in batches with a certain specification, an authoritative organization should be entrusted to carry out the following performance tests:
① The opening and closing torque of the valve under working pressure
② Under working pressure conditions, the number of continuous opening and closing of the valve for closing the valve well should be guaranteed.
③ The detection of the flow resistance coefficient of the valve under the condition of water delivery in the pipeline
2. The following tests should be performed for valves before leaving the factory:
① When the valve is open, the valve body should withstand the internal pressure test that is twice the valve's working pressure.
② When the valve is closed, both sides of the valve bear 11 times the valve's working pressure value, and there is no leakage. However, the leakage value of the metal-seated butterfly valve is not greater than the relevant requirements.
Internal and external corrosion protection of the valve
1. The inside and outside of the valve body including the variable speed transmission box should be shot blasted to clean the sand and rust, and use electrostatic spray the powdery non-toxic epoxy resin with a thickness from 0 to 3 mm. When it is difficult to electrostatically spray non-toxic epoxy resin for valves with extra-large sizes, similar non-toxic epoxy paint should be brushed or sprayed.
2. The inside of the valve body and the various parts of the valve plate require comprehensive anti-corrosion. On the one hand, the valve will not rust when it is immersed in water, and there will be no electrochemical corrosion between the two metals; on the other hand, the surface should be smooth to reduce the water resistance.
3. The sanitary requirements of the anticorrosive epoxy resin or paint in the valve body shall have the inspection report of the corresponding authority. The chemical and physical properties should also meet the relevant requirements.
The packaging and transportation of the valve
1. Lightweight blocking plates should be installed on both sides of the valve for sealing.
2. Valves with medium and small diameters should be bundled with straw ropes and transported in containers.
3. Valves with large diameters should be packaged with simple wooden boxes to avoid damage during transportation.
Checking the factory instructions of the valve
The valve is a device. The following relevant data should be indicated in the factory manual: valve specifications, models, working pressure, manufacturing standards, materials of valve bodies, valve stems, sealing, valve shaft packing and valve stem bushing, internal and external anti-corrosion materials, operating directions, turning numbers, opening and closing torque under working pressure conditions, names of manufacturers, dates of manufacture, manufacturing numbers, weights, effective opening and closing times, flow resistance coefficients of valves, relevant inspection data of valve factories and points for attention for installation and maintenance, etc.
