Views: 213 Author: Site Editor Publish Time: 2021-07-07 Origin: Site
Pneumatic valve is a kind of valve driven by compressed air. Because of its small size, large adjustable ratio, and good sealing effect, pneumatic valve has been widely used to control gas, steam, liquid and other media, and it has been widely used by market users. So what are the technical requirements when choosing a pneumatic valve to make the pneumatic valve play a greater role?
1.1 The specifications and categories of pneumatic valves shall meet the requirements of the pipeline design documents.
1.2 The model of the air actuator valve should be marked with the national standard number requirement. If it is a corporate standard, the relevant description of the model should be indicated.
1.3 The working pressure of the pneumatic valve is required to be greater than or equal to the working pressure of the pipeline. Under the premise of not affecting the price, the pressure that the valve can withstand should be greater than the actual working pressure of the pipeline; any side of the air actuated control valve should be able to withstand 1.1 times the valve when it is closed working pressure value without leakage; when the valve is open, the valve body should be able to withstand twice the valve working pressure.
1.4 Air actuator control valve manufacturing standards should be stated the national standard number on which it is based. If it is a corporate standard, the purchase contract should include corporate documents.
2.1 The material of the valve body should be mainly ductile iron. The grade and actual physical and chemical test data of the cast iron should be indicated.
2.2 Stem material, strive for stainless steel stem (2CR13), large diameter valves should also be stainless steel embedded stem.
2.3 The nut material is made of cast aluminum brass or cast aluminum bronze, and the hardness and strength are greater than the valve stem.
2.4 The material of the valve stem bushing shall have a hardness and strength not greater than that of the valve stem, and shall not form electrochemical corrosion with the valve stem and valve body under water immersion conditions.
2.5 Material of sealing surface
① Pneumatic valves are of different types, sealing methods and material requirements are different;
② For ordinary wedge gate valves, the material, fixing method and grinding method of the copper ring shall be explained;
③Physical, chemical and hygienic testing data of soft sealing gate valve and valve plate lining material, shall be indicated;
④ Actuated butterfly valve should be marked with the sealing surface material on the valve body and the sealing surface material on the butterfly plate; their physical and chemical test data, especially the hygienic requirements of rubber, anti-aging performance, and wear resistance; usually nitrile rubber and EPDM For rubber. It is strictly prohibited to mix recycled rubber.
2.6 Valve shaft packing
① Because the pneumatic operated gate valve in the pipe network are usually opened and closed infrequently, the packing is required to be inactive for several years, and the packing does not age, and the sealing effect is maintained for a long time;
② The globe valve with pneumatic actuator shaft packing should also have good sealing effect when subjected to frequent opening and closing;
③ In view of the above requirements, the valve shaft packing shall not be replaced for life or more than ten years;
④ If the packing needs to be replaced, the pneumatic valve design should be considered measures that can be replaced under water pressure.
3.1 The material of the box body and the internal and external anti-corrosion requirements are consistent with the valve body principle.
3.2 The box body should have sealing measures, and the box body can withstand 3 meters of water column immersion after assembly.
3.3 The adjustment nut of the opening and closing limit device on the box body should be inside or outside the box, but special tools are required for operation.
3.4 The design of the transmission structure is reasonable. It can only drive the valve shaft to rotate when opening and closing without moving up and downing, and the transmission parts will bite properly, and there will be no separation and slippage when opening and closing with load.
3.5 The variable speed transmission box body and the valve shaft seal cannot be connected into a leak-free whole, otherwise reliable measures to prevent leakage should be provided.
3.6 There is no debris in the box, and the gear bite part should be protected by grease.
4.1 The opening and closing direction of the pneumatic valve should always be closed clockwise.
4.2 Since the pneumatic valves in the pipe network are often opened and closed manually, the number of opening and closing revolutions should not be too much, even for large-diameter valves, it should be within 200-600 revolutions.
4.3 In order to facilitate the opening and closing operation of one person, the maximum opening and closing torque should be 240N-m under the pipeline pressure condition.
4.4 The opening and closing end of the pneumatic 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 roulette are not suitable for underground pipe networks.
4.5 Display panel for opening and closing degree of pneumatic valve
① The scale line of the degree of opening and closing of the pneumatic valve should be cast on the gearbox cover or on the shell of the display panel after changing the direction. All face to the ground, and the scale line should be painted with phosphor.
② The material of the indicator disc needle can be made of stainless steel plate under good management, otherwise it is painted steel plate. Do not use aluminum skin;
③The indicator disc needle is fixed firmly. Once the opening and closing adjustment is accurate, it should be locked with rivets.
4.6 If the pneumatic valve is buried deeply, and the distance between the operating mechanism and the display panel is greater than or equal to 1.5m from the ground, an extension rod facility should be provided, and it should be firmly fixed so that people can observe and operate from the ground. In other words, the opening and closing of valves in the pipe network is not suitable for downhole operations.
5.1 When a valve of a certain specification is manufactured in batches, 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 continuous opening and closing times of the valve can be guaranteed to close tightly;
③The detection of the flow resistance coefficient of the valve under the condition of pipeline water delivery.
5.2 The globe control valve with pneumatic actuator and smart positioner should be tested as follows before leaving the factory:
① When the valve is open, the valve body should withstand the internal pressure test that is twice the valve working pressure;
② When the valve is closed, both sides bear 1.1 times the valve working pressure value, and there is no leakage; however, the leakage value of the metal-sealed pneumatic butterfly valve is not greater than the relevant requirements.
6.1 The inside and outside of the valve body (including the variable-speed transmission box) should be shot blasted to remove the sand and rust firstly, and strive to electrostatically spray powdered 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, brush or spray similar non-toxic epoxy paint.
6.2 The inside of the valve body and all parts of the valve plate are required comprehensive anti-corrosion. On the one hand, it will not rust when immersed in water, and there will be no electrochemical corrosion between the two metals; on the other hand, the surface is smooth to reduce the water resistance.
The above are the requirements and methods for purchasing actuator pneumatic valve. I hope to provide help and guidance for your understanding and product selection.
