Principle and function of pneumatic check valve
Pneumatic check valve is the use of compressed air driven valve. Pneumatic valve procurement only clear specifications, type, working pressure to meet the procurement requirements of gas law, in the current market economy is not perfect. Because the air valve manufacturers in order to product competition, each in the design of the pneumatic valve, the idea of different, the formation of their own corporate standards and product personality. Therefore, in the purchase of pneumatic valve more detailed technical requirements, with the manufacturers to achieve consensus, as the annex to the pneumatic valve procurement contract is very necessary. This type of valve in the pipeline in general should be horizontal.
General requirements for pneumatic check valve
1, the production of pneumatic valve specifications and categories, should comply with the requirements of pipeline design documents.
2, pneumatic valve type should be indicated on the basis of the national standard code requirements. If the enterprise standard, should indicate the type of the relevant instructions.
3, pneumatic pressure valve, the working pressure is more than or equal to the pipeline, in does not affect the price of the premise, the valve can withstand the working pressure should be greater than the actual pipeline working pressure; pneumatic valve closing conditions of any side should be able to withstand 1.1 times the value of the valve working pressure and no leakage; valve open condition, the valve should be able to withstand twice the working pressure valve requirements.
4, pneumatic valve manufacturing standards, should be explained on the basis of the national standard number, if the enterprise standards, procurement contracts should be attached to corporate documents.
Pneumatic check valve material
1, the body material, should be ductile iron based, and indicate the actual physical and chemical testing data and cast iron.
2, the valve stem material, and strive to stainless steel stem (2CR13), large diameter valve should also be stainless steel embedded in the valve stem.
3, nut material, brass or cast aluminum with cast aluminum bronze, and the hardness and strength are greater than the stem.
4, the stem bushing material, its hardness and strength are not greater than the stem, and in the water immersion conditions and the valve stem, the body does not form an electrochemical corrosion.
5, sealing surface material:
Pneumatic valve type is different, sealing and material requirements;
Ordinary wedge type gate valve, copper ring material, fixed way, grinding method should be explained;
Soft sealing gate valve, valve plate lining rubber material of physical chemistry and health inspection data;
The valve shall be marked with the valve body sealing cover material and the butterfly plate sealing surface material; their physical and chemical test data, especially rubber, health requirements, aging resistance, wear resistance; it is forbidden to mix with recycled rubber.
6, valve shaft packing:
Due to the pipe network in the pneumatic valve, usually open and close the valve is not frequent, asked the packing in a few years, the packing is not aging, long-term maintenance sealing effect;
Valve shaft packing should also be under the frequent opening and closing, sealing effect of the good;
In view of the above requirements, the valve shaft packing is not for life, or more than a decade without replacement;
The packing for replacement, the pneumatic valve should be designed to have a situation of pressure change measures.  
Transmission box
1, box material and internal and external anti-corrosion requirements and body principles.
2, the box should be sealed measures, after the assembly can withstand the 3 m water column of the water immersion.
Hoist limit devices 3, the box body, the adjustment nut should be in the box or located in the outside box, but special tools need to be working.
4, the transmission structure design is reasonable, open and close can only drive the valve shaft rotation, does not make it up and down the channeling, the transmission parts of the appropriate, does not produce with load opening and closing when the separation skid.
5, the transmission box and the valve shaft seal can not be connected to the whole, otherwise it should be reliable leakage prevention measures.
6, the box body without debris, gear bite parts should be lubricated.
Operation mechanism of pneumatic check valve
1, the opening and closing direction of the pneumatic valve operation, all should be clockwise closing.
2, due to the gas pipe network in the valve, often manually opening and closing, opening and closing speed should not be too much, that is, large-diameter valves should also be within the 200-600 turn.
3, in order to facilitate opening and closing operation of a person, the plumber pressure conditions, the maximum torque should open and close to 240N-m.
4, pneumatic valves open and close operation of client should mortise and tenon and the size standard, and facing the ground so that people from the ground can direct the operation. The valve is not suitable for the underground pipe network.
5, the valve opening and closing the valve opening and closing of the display panel
Air valve opening and closing level of the calibration line, should be cast in the transmission cover or the conversion direction of the display panel on the shell, all face to the ground, the scale line brush on the fluorescent powder, to show marked;
II. The material of the indicating plate is used in the case of better management. Otherwise, it will not be used in the case of the paint;
In order to fix the needle, the needle is fixed and reliable, and once the opening and closing control is adjusted, it should be locked by the lock.
4.6 if the pneumatic valve buried deeper, operating mechanism and display disc from the ground distance is more than or equal to 1.5 m, a lengthening bar facilities, and stability in prison so that people from the ground observation and operation. In the case of the valve opening and closing operation of the network, not to the next well.
Performance test of pneumatic check valve
1, the valve a specification of the bulk manufacturing, should be entrusted to the authority of the organization for the following performance testing:
Valve opening and closing torque under the condition of working pressure;
II in the working pressure, to ensure that the valve closed tight continuous opening and closing times;
Detection of the flow resistance coefficient of the valve in the pipe flow.
2, the valve should be carried out before the following detection:
Valve in the open position, the valve should be under the pressure of two times the valve pressure test;
II valve closed, the two sides were 1.1 times the valve pressure, no leakage; but the metal sealing butterfly valve, leakage value is not greater than the relevant requirements.
Internal and external anti-corrosion of pneumatic check valve
1, valve body (including the variable speed transmission box) inside and outside, at first, blasting sand blasting, seek non-toxic powder electrostatic spraying epoxy resin, thickness of 0.3mm. Large type electrostatic spraying non-toxic epoxy resin has a difficult time, should also be painted, similar to the non-toxic epoxy paint.
2, the internal body and all parts of the valve plate requirements of a comprehensive anti-corrosion, hand immersed in water will not rust, between the two metal does not produce electrochemical corrosion; two aspects of smooth surface of the water resistance reduced.
3, the body of the anti-corrosion epoxy resin or paint health requirements, should have the appropriate authority of the inspection report. Chemical physical properties should also be in accordance with the relevant requirements.
Pneumatic check valve package transportation
1, the valve should be located on both sides of a light blocking plate fixation.
2, the small caliber valve should be tied to rope, and transportation to the container as appropriate.
3, summary of large diameter valves are also the framework of solid wood packaging, so as to avoid damage during transport collision.