Pneumatic valves and electric valves

In my opinion, if it is convenient to access an air source and there are no special requirements, pneumatic control valves should be used whenever possible, as electric control valves are difficult to maintain

Reply to 2# heartoking: But if pneumatic technology is used, instrument air needs to be taken into account, and the cost would be too high

I think there isn’t a specific standard for this; it depends on the manufacturing process and the customer’s budget

The original poster is wrong; the air source is available, but the torque is not high. To achieve rapid adjustment, pneumatic systems must be used, and moreover, they are more energy-efficient as well.

In terms of energy savings, electric valves are more energy-efficient. From a safety perspective, pneumatic valves are safer! And they are also easier to maintain!

Agree with the person on floor 6. Electric valves are being used more and more these days, and the technology related to them has also become mature. Pneumatic valves require a gas supply; they offer high safety levels, but this is not necessary if only a few valves are used. Nowadays, some electric valves come with quite high protection and explosion-proof ratings

Agree with the fourth floor’s view; it depends on the manufacturing process and operating conditions

Reply to 1# Lan Huan'er: It depends on what you do. If it’s a high-risk industry where the generation of electric sparks is not allowed, pneumatic systems should be used as they are safer and more reliable. If there are no particular requirements, the electric version is more convenient

If the gas supply is readily available, it is recommended to use pneumatic valves. The advantages are: 1. Long service life and no need for maintenance; 2. Suitable for explosion-proof environments

Pneumatic valve: A valve driven by compressed air. The practice of meeting the requirements for purchasing pneumatic valves by merely specifying their specifications, categories, and operating pressure is inadequate in today’s market economy. As pneumatic valve manufacturers compete with one another, they each introduce innovations within the framework of a unified design approach for such valves, resulting in their own corporate standards and unique product characteristics. Therefore, it is highly necessary to specify detailed technical requirements when purchasing pneumatic valves, reach a consensus with the manufacturer through coordination, and include these requirements as an attachment to the purchase contract for pneumatic valves. General requirements for editing this section: 1.1 The specifications and categories of pneumatic valves shall meet the requirements specified in the pipeline design documents. 　　1.2 The model of the pneumatic valve shall indicate the requirements of the relevant national standard number. If it is a corporate standard, relevant specifications for the model should be indicated. 　　1.3 The operating pressure of the pneumatic valve should be ≥ the operating pressure of the pipeline; provided that it does not affect the price, the pressure that the valve can withstand should be higher than the actual operating pressure of the pipeline ； Either side of the pneumatic valve when it is closed should be able to withstand 1.1 times the working pressure of the valve without leaking ； With the valve open, the valve body shall be able to withstand a pressure twice that of the valve’s operating pressure. 　　1.4 The manufacturing standards for pneumatic valves shall specify the corresponding national standard numbers; if it is a corporate standard, the relevant corporate documents shall be attached to the purchase contract. Edit this section: Specifications for pneumatic valves 2.1 The material of the valve body should be ductile iron, with the grade specified along with the actual physical and chemical test data of the iron. 　　2.2 Valve stem material: stainless steel valve stems (2CR13) are preferred; for large-diameter valves, valve stems with a stainless steel core should also be used. 　　2.3 The material of the nut is cast aluminum brass or cast aluminum bronze, with hardness and strength both greater than those of the valve stem. 　　 For pneumatic valves, 2.4 The material of the valve stem bushing should have a hardness and strength that are not greater than those of the valve stem, and it should not cause electrochemical corrosion in conjunction with the valve stem and valve body when exposed to water. 　　2.5 Material of the sealing surface ① Pneumatic valves come in different types, resulting in varying sealing methods and material requirements ； 　　②For ordinary wedge-type gate valves, the material of the copper ring, its fixing method, and the grinding method should all be specified ； 　　③Physical, chemical, and hygiene test data of the rubber-lined material used in soft-sealed gate valves ； 　　④The butterfly valve should indicate the material of the sealing surface on the valve body and the material of the sealing surface on the butterfly disc ； Their physicochemical test data, particularly the hygiene requirements for rubber, aging resistance, and wear resistance ； Nitrile rubber and EPDM are commonly used; the use of recycled rubber is strictly prohibited. 　　2.6 Valve shaft packing 　　① Since pneumatic valves in piping systems are usually not opened and closed frequently, it is required that the packing remain inactive for several years, do not age, and maintain its sealing properties over time ； 　　②The valve shaft packing should also maintain good sealing performance under frequent opening and closing ； 　　③Given the above requirements, the valve shaft packing is designed to remain unchanged for life or for over a decade ； 　　④If the filler needs to be replaced, the design of the pneumatic valve should take into account measures for replacement under water pressure. Pneumatic valve diaphragm. Edit this section: Transmission box. 3.1 The material of the box, as well as the requirements for internal and external corrosion protection, are consistent with those applicable to the valve body. 　　3.2 The enclosure shall have sealing measures, and it must be able to withstand immersion under a 3-meter water column pressure after assembly. 　　3.3 The opening and closing limit device on the box shall have its adjustment nuts either inside the box or outside it, but special tools are required to operate it. 　　3.4 The transmission structure is reasonably designed; it allows the valve shaft to rotate only during opening and closing, preventing it from moving up and down. The fit between the transmission components is appropriate, so there is no separation or slippage when operating under load. 　　3.5 The transmission housing and the valve shaft seal must not be connected to form a leak-free unit; otherwise, reliable measures to prevent leakage must be in place. 　　3.6 There should be no debris inside the box, and the gear engagement areas must be protected with lubricant. Edit this section: Operating mechanism of pneumatic valves 4.1 The closing direction of a pneumatic valve during operation should always be clockwise. 　　4.2 Due to the pneumatic valves in the pipeline network, which are often operated manually, the number of operations should not be excessive; even for large-diameter valves, it should remain between 200 and 600 rotations. 　　4.3 To facilitate operation by a single person, under normal piping conditions, the maximum opening and closing torque should be 240 N-m. 　　4.4 The operating end of the pneumatic valve should be fitted with square tenons, have standardized dimensions, and face downward so that it can be operated directly from the ground. Valves with wheels are not suitable for underground piping systems. 　　 Pneumatic valve 4.5 Display panel for the degree of opening/closing of the pneumatic valve ① The scale lines indicating the degree of opening/closing of the pneumatic valve should be cast on the gearbox cover or on the housing of the display panel after direction change; they must all face downward. The scale lines are coated with fluorescent powder to ensure visibility ； 　　②In well-managed facilities, the material for the dial needle can be stainless steel plates; otherwise, painted steel plates should be used. Aluminum sheets must not be used for this purpose ； 　　③The dial needle is eye-catching and firmly fixed; once the opening and closing adjustment is accurate, it should be locked with rivets. 　　4.6 If the pneumatic valve is buried deep, with the operating mechanism and display panel at a height of ≥1.5m above the ground, an extension rod should be provided and fixed securely, so that it can be observed and operated from the ground level. In other words, the operation of opening and closing valves in the pipeline network should not be carried out by working down in the well. 5.1 When valves of a certain specification are manufactured in bulk, an authoritative institution should be commissioned to conduct tests on the following performance parameters: ① The opening and closing torque of the valve under operating pressure conditions ； 　　②Number of consecutive opening and closing cycles under working pressure that can ensure a tight seal of the valve ； 　　③Measurement of the flow resistance coefficient of valves under pipeline water conveyance conditions. 　　5.2 Before leaving the factory, the valves shall undergo the following tests: ① With the valve in the open position, the valve body shall be subjected to an internal pressure test equal to twice the working pressure of the valve ； 　　②With the valve closed, each side is subjected to 1.1 times the working pressure of the valve, with no leakage ； However, for butterfly valves with metal seals, the leakage rate is also no greater than the relevant requirements. Editing this section: Corrosion protection for the inside and outside of pneumatic valves 6.1 On the inside and outside of the valve body (including the gearbox), sandblasting should be carried out first to remove rust, followed by the application of electrostatic spraying of non-toxic powdered epoxy resin, with a thickness of at least 0.3 mm. When it is difficult to use electrostatic spraying with non-toxic epoxy resin for extra-large valves, similar non-toxic epoxy paint should be applied by brushing or spraying. 　　6.2 The interior of the valve body as well as all parts of the valve disc must be fully protected against corrosion; they should not rust when immersed in water, and no electrochemical corrosion should occur between the different metals ； Secondly, the smooth surface reduces water resistance. For pneumatic valves, 6.3 The hygiene requirements regarding the epoxy resin or paint used for corrosion protection inside the valve body must be supported by test reports from relevant authoritative agencies. The chemical and physical properties must also meet the relevant requirements. Edit this section: Packaging and transportation of pneumatic valves 7.1 Light blocking plates should be installed on both sides of the valve to secure it in place. 　　7.2 Valves of medium and small diameter should be tied with straw ropes and transported in containers. 　　7.3 Large-diameter valves also come with a simple wooden frame for solid packaging, to prevent damage during transportation. Edit this section: Instructions for use of pneumatic valves Pneumatic valves are types of equipment, and the following relevant data should be specified in their instructions for use: Valve specifications ； Model ； Work stress ； Manufacturing standards ； Valve body material ； Valve stem material ； Sealing material ； Valve stem packing material ； Material of valve stem bushing ； Internal and external anti-corrosion materials ； Operation start direction ； RPM ； Opening and closing torque under working pressure ； Name of the manufacturing factory ； Date of manufacture ； Factory serial number ； Weight ； Bore diameter, number of holes, and center hole spacing of the connection flange ； Indicate the control dimensions of length, width, and height in a graphical manner ； Valve flow resistance coefficient ； Effective opening and closing cycles ； Data related to the factory testing of valves, as well as precautions for installation and maintenance. Edit this section: Classification of Pneumatic Valves
I. Main types of pneumatic valves:
1) Pneumatic V-type control ball valve
2) Pneumatic O-type shut-off ball valve
3) Torque-type cylinder ball valve
4) Electromagnetic diaphragm valve
5) Pneumatic straight-stroke diaphragm valve
6) Electric valve

II. Pneumatic V-type control valve:
Applications and features
A. Applications: It features a right-angle rotary structure; when used in conjunction with a valve positioner, it enables proportional control ； The V-type spool is most suitable for various control applications, featuring a high rated flow coefficient, a large adjustment range, excellent sealing performance, sensitive control characteristics, a small size, and the ability to be installed in either vertical or horizontal orientation. Suitable for controlling media such as gases, vapors, and liquids. 　　B. Features: It is a right-angled rotary structure, consisting of a V-shaped valve body, a pneumatic actuator, a positioner, and other accessories ； There is an inherent flow characteristic that is approximately in a 100:1 ratio ； It features a dual-bearing structure, resulting in low starting torque, along with excellent sensitivity and response speed ； Superior shear strength. 　　C. The pneumatic piston actuator uses compressed air as the power source; the movement of the piston drives the crank arm to rotate 90 degrees, thereby enabling the valve to open and close automatically. Its components include: adjustment bolt, actuator housing, crank arm, cylinder block, cylinder shaft, piston, connecting rod, and universal joint. 　　D. Working principle of pneumatic control valves: A pneumatic control valve consists of an actuator and a control mechanism. The actuator is the thrust component of the control valve; it generates a corresponding thrust based on the pressure of the control signal, thereby driving the control mechanism to move. The valve body is the regulating component of a pneumatic control valve; it comes into direct contact with the fluid being regulated in order to control the flow rate of that fluid. Edit this section: Summary of standards for pneumatic valves Standard Number Chinese Name of the Standard English Name of the Standard Review: Rubber seals for pneumatic valves – Groove dimensions and tolerances Review: Rubber seals for pneumatic valves – Size series and tolerances ANSI/NFPA T 3.21.4 R2-2000 Pneumatic valves; NFPA/T 2.6.1 R2-2000 Supplement: Pressure ratings for fluid power components – Method for verifying fatigue and determining burst pressure ratings of the pressure-containing envelope of metal fluid power pneumatic valves BS 4151-1967 Method of evaluating pneumatic valve positioners with an input signal of 3 to 15 lbf/in Edit this section: Parameter definitions 1. Nominal diameter: Also known as mean outside diameter, it is denoted by the symbol DN; it represents the standard diameter for various pipes and piping fittings. Tubes and piping fittings of the same nominal diameter can be connected to each other, allowing for interchangeability. It is not the actual outer or inner diameter of the pipe; although its value is close to or equal to the pipe’s inner diameter, the nominal diameter (also known as nominal bore or nominal size) is used to standardize the connection dimensions of tubes and fittings. For example, welded steel pipes can be classified by thickness into thin-walled pipes, ordinary pipes, and thick-walled pipes. Its nominal diameter is neither the outer diameter nor the inner diameter, but rather a nominal size that is close to the inner diameter of ordinary steel pipes. For each nominal diameter, there is a corresponding outer diameter, while the inner diameter value varies depending on the thickness. The nominal diameter can be expressed in metric mm or imperial inches. Piping fittings are also indicated by nominal diameter, with the same meaning as welded pipes. 　　2. Nominal pressure: (Nominal pressure), denoted by the symbol PN, refers to the maximum operating pressure allowed when the component is used at a certain temperature. For control valves with carbon steel bodies, it refers to the maximum operating pressure permitted for use at temperatures below 200°C ； For cast iron valve bodies, it refers to the maximum operating pressure allowed for use at temperatures below 120°C ； For control valves with stainless steel valve bodies, it refers to the maximum operating pressure permitted for use at temperatures below 250°C. As the operating temperature increases, the pressure resistance of the valve body decreases. For example, a carbon steel control valve with a nominal pressure of 6.4 MPa (PN64) has a pressure resistance of 5.2 MPa at 300°C, 4.1 MPa at 400°C, and 2.9 MPa at 450°C. Therefore, the determination of the nominal pressure of a control valve must take into account not only the maximum operating pressure but also the maximum operating temperature and the material properties, rather than simply requiring that the nominal pressure be higher than the operating pressure.