General requirements for pneumatic check valve:

 

1. The specifications and types of pneumatic valves shall meet the requirements of pipeline design documents.

2. The model of pneumatic valve shall indicate the national standard number requirements. If it is an enterprise standard, the relevant description of the model should be indicated.

3. The working pressure of the pneumatic valve is required to be greater than or equal to the working pressure of the pipeline. On 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 pneumatic valve under the closed condition should be able to bear 1.1 times the working pressure of the valve without leakage; the valve body should be able to bear twice the working pressure of the valve under the open condition.

4. The manufacturing standard of pneumatic valve shall state the national standard number. If it is an enterprise standard, the enterprise document shall be attached to the purchase contract.
 

Material of pneumatic check valve:

1. The valve body material should be mainly ductile iron, and the brand and the actual physical and chemical test data of cast iron should be indicated.

2. The stem material shall be stainless steel stem (2Cr13), and the large diameter valve shall also be stainless steel embedded stem.

3. The nut 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 hardness and strength of the valve stem bushing material should not be greater than that of the valve stem, and there is no electrochemical corrosion with the valve stem and valve body under the condition of water immersion.

5. Material of sealing surface:

① There are different types of pneumatic valves, sealing methods and material requirements;

② Common wedge gate valve, copper ring material, fixed way, grinding way should be explained;

③ Physicochemical and hygienic test data of soft seal gate valve and valve plate rubber lining materials;

4. The butterfly valve should mark the material on the sealing surface of the valve body and the material of the sealing cover on the butterfly plate; their physical and chemical test data, especially the hygienic requirements, anti-aging and wear-resisting properties of the rubber, and strictly prohibit the addition of reclaimed rubber.

6. Valve shaft packing:

① As the pneumatic valve in the pipe network is usually opened and closed infrequently, the packing is required to be inactive for several years, and the packing is not aging, so as to maintain the sealing effect for a long time;

② Valve shaft packing should also bear frequent opening and closing, good sealing effect;

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 consider the replacement measures under the condition of water pressure.

Gearbox:
 

1. The material of the box and the requirements of internal and external anti-corrosion are consistent with the principle of valve body.

2. The box body shall be sealed and can withstand the immersion of 3M water column after assembly.

3. For the opening and closing limit device on the box, its adjusting nut should be in the box or outside the box, but it can only be operated with special tools.

4. The design of transmission structure is reasonable. When opening and closing, it can only drive the valve shaft to rotate, not make it move up and down. The driving parts bite properly, and there is no separation slip when opening and closing with load.

5. Transmission box and valve shaft seal should not be connected as a whole without leakage, otherwise reliable anti leakage measures should be taken.

6. There shall be no foreign matters in the box, and the gear engagement part shall be protected by grease.

Operating mechanism of pneumatic check valve:

1. The opening and closing direction of pneumatic valve should be closed clockwise.

2. As the pneumatic valves in the pipe network are often opened and closed manually, the number of opening and closing turns should not be too much, even the large-diameter valves should be within 200-600 turns.

3. In order to facilitate one person's opening and closing operation, under the condition of plumber's pressure, the large opening and closing torque should be 240n-m.

4. The opening and closing operation end of pneumatic valve shall be square tenon with standardized size and facing the ground, so that people can operate directly from the ground. Valves with wheels are not suitable for underground pipe networks.

5. Display panel of opening and closing degree of pneumatic valve

① The scale mark of the opening and closing degree of the pneumatic valve shall be cast on the gearbox cover or the shell of the display panel after changing direction, all of which shall face the ground, and the scale mark shall be brushed with fluorescent powder to show eye-catching

② Stainless steel plate can be used in the case of good management, otherwise it is painted steel plate, and aluminum sheet should not be used;

③ The indicator disc needle is eye-catching and fixed firmly. Once the opening and closing adjustment is accurate, it should be locked with rivets.

4.6 if the pneumatic valve is deeply buried and the distance between the operating mechanism and the display panel and the ground is greater than or equal to 1.5m, the extension rod facilities shall be set and fixed firmly, so that people can observe and operate from the ground. That is to say, the valve in the pipe network is not suitable for operation in the well.

Performance test of pneumatic check valve:
 

1. When a certain specification of valve is manufactured in batch, the following performance tests shall be conducted by an authoritative organization:

① The opening and closing torque of the valve under working pressure;

② Under the working pressure condition, the valve can be closed tightly for continuous opening and closing times;

③ Detection of flow resistance coefficient of valve under the condition of pipeline water delivery.

2. The valve shall be tested as follows before delivery:

① When the valve is open, the valve body shall bear the internal pressure detection of twice the working pressure of the valve;

② When the valve is closed, both sides bear 1.1 times the working pressure of the valve respectively, and there is no leakage; however, for the butterfly valve with metal seal, the leakage value is not greater than the relevant requirements.

Internal and external corrosion protection of pneumatic check valve:
 

1. The inside and outside of the valve body (including the transmission box) should be shot blasted to remove sand and rust, and electrostatic spraying of powdery non-toxic epoxy resin with a thickness of more than 0.3mm should be made. When it is difficult to spray non-toxic epoxy resin by electrostatic spraying for extra large valves, similar non-toxic epoxy paint should be applied.

2. On the one hand, immersion in water will not rust and electrochemical corrosion will not occur between the two metals; on the other hand, smooth surface will reduce water resistance.

3. According to the hygienic requirements of epoxy resin or paint for anti-corrosion in valve body, the inspection report of corresponding authority shall be provided. The chemical and physical properties should also meet the relevant requirements.

Packing and transportation of pneumatic check valve:
 

1. Both sides of the valve shall be sealed with light blocking plate.

2. Medium and small diameter valves should be bound with straw rope and transported in containers.

3. Large diameter valves also have simple solid packing with wooden frame to avoid damage during transportation.

Pneumatic check valve is a valve driven by compressed air. When purchasing pneumatic valve, it is not perfect in the current market economy environment that only the specification, type and working pressure are specified to meet the purchasing requirements. For the sake of product competition, the manufacturers of pneumatic valves carry out different innovations under the concept of unified design of pneumatic valves, forming their own enterprise standards and product personality. Therefore, it is very necessary to put forward the technical requirements in detail when purchasing the pneumatic valve and reach a consensus with the manufacturer as an annex to the pneumatic valve purchase contract. This kind of valve should be installed horizontally in the pipeline.

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