General requirements for pneumatic check valves　　
1. The specifications and categories of pneumatic valves produced should comply with the requirements of the pipeline design documents.
2. The model of the pneumatic valve should indicate the national standard number requirements it is based on. If it is an enterprise standard, the relevant description of the model should be indicated.
3. The working pressure of pneumatic valves should be ≥ the working pressure of the pipeline. Without affecting the price, the working pressure that the valve can withstand should be greater than the actual working pressure of the pipeline; Either side of the pneumatic valve should be able to withstand 1.1 times the valve working pressure without leakage when it is closed; When the valve is open, the valve body should be able to withstand twice the working pressure of the valve.
4. The manufacturing standards for pneumatic valves should specify the national standard number they are based on. If it is an enterprise standard, the procurement contract should be accompanied by the enterprise document.
Pneumatic check valve material
1. The valve body material should be mainly ductile iron, and the grade and actual physical and chemical testing data of the cast iron should be indicated.
2. The valve stem material should strive for stainless steel stem (2CR13), and large-diameter valves should also have stainless steel embedded stem.
3. The nut material is made of cast aluminum brass or cast aluminum bronze, and its hardness and strength are greater than those of the valve stem.
4. The material of the valve stem liner should have a hardness and strength not greater than that of the valve stem, and should not form electrochemical corrosion with the valve stem and valve body when immersed in water.
5. Material of sealing surface:
① Pneumatic valves come in different categories, with varying sealing methods and material requirements;
② The material, fixing method, and grinding method of the copper ring for ordinary wedge gate valves should be specified;
③ Physical, chemical, and hygiene testing data for soft sealed gate valves and valve plate lining materials;
④ Butterfly valves should indicate 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 sanitary requirements, anti-aging performance and wear resistance of rubber; It is strictly prohibited to mix recycled rubber.
6. Valve shaft packing:
① Due to the infrequent opening and closing of pneumatic valves in the pipeline network, it is required that the packing should remain inactive for several years, and the packing should not age to maintain its sealing effect for a long time;
② The valve shaft packing should also have good sealing performance when subjected to frequent opening and closing;
③ In view of the above requirements, the valve shaft packing should be kept unchanged for life or more than ten years;
④ If the packing needs to be replaced, the design of the pneumatic valve should consider measures to replace it under water pressure conditions.
Pneumatic check valve gearbox
1. The material of the box and the requirements for internal and external anti-corrosion are consistent with the principles of the valve body.
2. The box should have sealing measures and be able to withstand immersion in a 3-meter water column after assembly.
3. The adjustment nut of the opening and closing limit device on the box should be located inside or outside the box, but special tools are required for operation.
4. The transmission structure is designed reasonably, which can only drive the valve shaft to rotate during opening and closing, without causing it to move up and down. The transmission components are moderately engaged, and there is no separation slip during load opening and closing.
5. The gearbox and valve shaft seal should not be connected as a leak free whole, otherwise reliable anti leakage measures should be taken.
6. There are no impurities inside the box, and the gear meshing area should be protected with lubricating grease.
Operating mechanism of pneumatic check valve
1. The opening and closing direction of pneumatic valves should always be clockwise.
2. Due to the fact that pneumatic valves in the pipeline network are often manually opened and closed, the opening and closing speed should not be too high, even for large-diameter valves, it should be within 200-600 revolutions.
3. For the convenience of one person's opening and closing operation, under the pressure of pipeline workers, a large opening and closing torque of 240N-m is recommended.
4. The opening and closing operation end of pneumatic valves should be square tenoned, standardized in size, and face the ground, so that people can directly operate from the ground. Valves with discs are not suitable for underground pipelines.
5. Display panel for the degree of opening and closing of pneumatic valves
① The scale line for the opening and closing degree of pneumatic valves should be cast on the gearbox cover or the outer shell of the display panel after changing direction, facing the ground uniformly. The scale line should be brushed with fluorescent powder to show visibility
② The material of the indicator disk needle can be stainless steel plate under good management, otherwise it is painted steel plate and aluminum sheet should not be used for production;
③ The indicator pin should be conspicuous and securely fixed. Once the opening and closing adjustment is accurate, it should be locked with rivets.
4.6 If the pneumatic valve is buried deep and the distance between the operating mechanism and display panel and the ground is ≥ 1.5m, an extension rod facility should be installed and firmly fixed for people to observe and operate from the ground. That is to say, the opening and closing of valves in the pipeline network is not suitable for underground operations.
Performance testing of pneumatic check valve
1. When mass manufacturing a certain specification of valve, authoritative institutions should be commissioned to conduct the following performance tests:
① The opening and closing torque of the valve under working pressure conditions;
② Under working pressure conditions, the continuous opening and closing times that can ensure the valve is tightly closed;
③ Detection of flow resistance coefficient of valves under pipeline water delivery conditions.
2. Valves should undergo the following tests before leaving the factory:
① When the valve is in the open position, the valve body should withstand an internal pressure test of twice the valve working pressure value;
② Under the closed condition of the valve, both sides can withstand 1.1 times the valve working pressure without leakage; But for metal sealed butterfly valves, the leakage value should not exceed the relevant requirements.
Internal and external anti-corrosion of pneumatic check valve
1. The inside and outside of the valve body (including the gearbox) should first be shot blasted, sandblasted, and rust removed, striving for electrostatic spraying of powder non-toxic epoxy resin with a thickness of at least 0.3mm. When it is difficult to electrostatically spray non-toxic epoxy resin on extra large valves, similar non-toxic epoxy paint should also be brushed or sprayed.
2. The interior of the valve body and various parts of the valve plate require comprehensive anti-corrosion measures. On the one hand, immersion in water will not corrode, and there will be no electrochemical corrosion between the two metals; Smooth surface on both sides reduces water resistance.
3. The hygiene requirements for anti-corrosion epoxy resin or paint inside the valve body should have corresponding authoritative testing reports. The chemical and physical properties should also meet relevant requirements.
Packaging and transportation of pneumatic check valves
1. Lightweight blocking plates should be installed on both sides of the valve for secure sealing.
2. Small and medium-sized valves should be tied with grass ropes and transported in containers.
3. Large caliber valves also come with simple wooden frame solid packaging to prevent damage during transportation.