What Is a Pneumatic Valve?
Pneumatic valves are valves driven by compressed air. When the pneumatic valve is purchased, only the specifications, categories, and working pressure are met to meet the procurement requirements. It can be used to control various types of fluids such as air, water, steam, various corrosive media, muds, oils, liquid metals, and radioactive media. flow. It is imperfect in the current market economy environment. Because of the competition of products, pneumatic valve manufacturers have each carried out different innovations under the concept of unified design of pneumatic valves, forming their own corporate standards and product personality. Therefore, in the purchase of pneumatic valves, technical requirements are presented in more detail, and a consensus is reached with the manufacturer. As an attachment to the purchase contract of pneumatic valves, it is very necessary. This type of valve should generally be installed horizontally in the pipeline.
Pneumatic valves
- Pneumatic valve is by means of compression
Compressed air is used to drive multiple sets of combined pneumatic pistons in the actuator to transmit force to the characteristics of the crossbeam and the inner curved track, which drives the hollow core spindle to perform rotary motion, and the compressed air gas plate is transmitted to each cylinder, and the inlet and outlet positions are changed to change the spindle rotation Direction, according to the required rotation torque of the load (valve), the number of cylinder combinations can be adjusted to drive the load (valve) to work.
- Two-position five-way solenoid valve is usually used in conjunction with double-acting pneumatic actuators. Two positions are controllable in two positions: on-off. Five-way has five channels of ventilation, one of which is connected to the air source, and the other two The inlet and outlet ports of the external air chamber of the acting cylinder are connected, and the two are connected to the inlet and outlet air ports of the internal air chamber. The specific working principle can refer to the working principle of the double acting pneumatic actuator. Due to the increasing number of control methods and means, there are many methods for controlling pneumatic actuators in actual industrial routines and industrial control. The following are commonly used.
- Intelligent display instrument Intelligent display instrument is used to monitor the working state of the valve and control the valve during the execution of the instrument. It monitors the working state of the valve through two position sensors, determines whether the valve is in the open or closed state, and records the valve by programming. The number of the switch, and there are two 4-20mA output corresponding to the valve opening and two-way normally open and normally closed output contacts. These output signals control the opening and closing of the valve.
- The application of the control system PLC in the control system is becoming more and more extensive. Since this solution is developed on the OMRON PLC, the OMRON PLC is used as an introduction.
- Hardware composition: 1 computer, 1 set of PLC (including CPU, I / O module, ID212, OC224, AD003 module), 2 relays, 2 solenoid valves, 1 pneumatic valve actuator.
- common enquiries
- 1. produced
- 1. The material of the valve body should be nodular cast iron, and indicate the grade and actual physical and chemical test data of the cast iron.
- 2. The material of the valve stem, strive for the stainless steel valve stem (2CR13), and the large-caliber valve should also be a stainless steel embedded valve stem.
- 3. Nut material: cast aluminum brass or cast aluminum bronze, with hardness and strength greater than the valve stem.
- 4. The material of the valve stem bushing should be no greater than the hardness and strength of the valve stem, and it should not form electrochemical corrosion with the valve stem and valve body under water immersion.
- 5. Material of sealing surface:
- Different types of pneumatic valves, different sealing methods and material requirements;
- For ordinary wedge gate valves, the material, fixing method and grinding method of the copper ring should be specified;
- 1. The material of the box body and the internal and external anticorrosion requirements are consistent with the principle of the valve body.
- 2. The box should have sealing measures. After the box is assembled, it can withstand 3 meters of water column soaking.
- 3, the opening and closing limit device on the box, the adjustment nut should be inside the box or outside the box, but special tools are required to work.
- 4. The transmission structure is designed reasonably. It can only drive the valve shaft to rotate during opening and closing. It will not cause it to move up and down. The transmission component will bite properly.
- 5. The transmission gear box and the valve shaft seal must not be connected to form a leak-free whole, otherwise there should be reliable measures to prevent cross-leakage.
- 6. There is no foreign matter in the box, and the gear meshing part should be protected by grease.
- 1. The opening and closing direction of the pneumatic valve should always be closed clockwise.
- 2. As the pneumatic valve in the pipe network is often manually opened and closed, the number of opening and closing revolutions should not be too much, that is, the large-caliber valve should also be within 200-600 revolutions.
- 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 condition of pipeline pressure.
- 4. The opening and closing operation end of the pneumatic valve should be a square tenon, and its size is standardized and facing the ground, so that people can directly operate from the ground. Valves with roulette are not suitable for underground pipe networks.
- 5.Display panel for opening and closing degree of pneumatic valve
- The scale of the opening and closing degree of the pneumatic valve should be cast on the gearbox cover or the casing of the display panel after the direction is changed, all of which should face the ground, and the scale should be brushed with fluorescent powder to show eye-catching;
- The material of the indicator needle can be made of stainless steel under better management; otherwise, it is painted steel, and it should not be made of aluminum skin;
- The indication needle is eye-catching and firmly fixed. Once the opening and closing adjustment is accurate, it should be locked with rivets.
- 6. If the pneumatic valve is buried deeper, when the distance between the operating mechanism and the display panel is 1.5m or more from the ground, an extension rod facility should be provided and fixed firmly so that people can observe and operate from the ground. In other words, the opening and closing of valves in the pipeline network is not suitable for downhole operations.
- 1. When a valve is manufactured in batches of a certain specification, an authoritative agency should be entrusted to perform the following performance testing:
- Opening and closing torque of the valve under working pressure;
- Under the condition of working pressure, it can ensure the continuous number of continuous opening and closing of the valve;
- Detection of flow resistance coefficient of valve under pipeline water delivery condition.
- 2, the valve should be tested before leaving the factory:
- When the valve is open, the valve body should withstand the internal pressure detection of twice the valve's working pressure value;
- Under the closed condition of the valve, the two sides bear 1.1 times the valve working pressure value without leakage; however, the leakage value of the metal-sealed butterfly valve is not greater than the relevant requirements.
- 1. Inside and outside the valve body (including the variable speed transmission box), firstly, shot blasting and sand removal should be performed, and strive to electrostatically spray powder non-toxic epoxy resin with a thickness of more than 0.3mm. When it is difficult to electrostatically spray non-toxic epoxy resin for oversized valves, similar non-toxic epoxy paint should also be applied by brushing and spraying.
- 2,
- 1. Light blocking plates should be provided on both sides of the valve for solid sealing.
- 2. Medium and small caliber valves should be bundled with straw ropes and transported in containers.
- 3. Large-caliber valves are also provided with simple wooden frame solid packaging to avoid damage during transportation.
- Pneumatic valves are equipment, and the following relevant data should be marked in the factory instructions:
- Valve specifications; Model; Working pressure; Manufacturing standards; Valve body material; Stem material; Seal material; Stem packing material; Stem sleeve material; Internal and external anticorrosive material; Operation starting direction; Number of revolutions; Opening and closing under working pressure Moment; manufacturer's name; date of manufacture; number of shipment; weight; diameter, number of holes, center hole distance of connecting flange; indicate the overall length, width, and height control size by diagram; valve flow resistance coefficient; effective Opening and closing times; relevant data for valve factory inspection and precautions for installation and maintenance.
- (1) Before the pneumatic valve is installed and used, the valve must be inspected before installation and the switch operation test. It can only be installed and used under normal operating conditions.
- (2) Install the pneumatic valve so that the valve and the pipeline flange are concentric as much as possible, and be supported and fixed. Do not subject the ball valve to other external forces, so as not to damage the valve's middle seal and deform the valve. Causes the valve switch to malfunction and the valve to be damaged and cannot be used.
- (3) It is necessary to ensure that the power source provided by the balloon valve and pneumatic components is clean and free of oil and water as much as possible. Cleanliness should be less than 0.4 microns.
- (4) Before connecting the air source, you must clean the air supply pipeline, air source interface, and switches and other components to prevent malfunctions caused by dirt and sediment rushing into the pneumatic execution unit due to unclean pipelines.
- (5) The connection of pneumatic actuators, solenoid valves, positioners, filters, pressure reducing valves, etc. can be copper or nylon. To prevent dust and reduce noise, the exhaust port should be installed with a muffler or muffler. Flow valve.
- (6) After installation, the pneumatic valve should be tested, pressurize the pneumatic actuator to the rated value, the pressure is 0.4 ~ 0.7mpa, perform the switch test on the pneumatic ball valve, and observe the opening and closing of the valve. It should rotate flexibly without jamming. If the switch is blocked, the air pressure can be increased. Repeat the switch to make the valve flexible.
- (7) When installing and adjusting the switch-type pneumatic valve, first use a manual device (manual button on the solenoid valve) to debug, and then power on to debug after the operation is normal.
- (8) The pneumatic valve should be maintained regularly. The valve stem should be refueled (oil) once every three months. Drain and drain the pneumatic actuator and the air filter used regularly. Under normal circumstances, check once every six months and check once a year.
- The valve is at the core of the pneumatic control system. There are various types of directional control valves (DCV) and proportional control valves to choose from. Directional control valves are undoubtedly the most commonly used valves. They control the direction of compressed air (or other suitable fluid), such as determining whether a cylinder's stroke is forward or backward.
- The valve is identified by the number of its main connections and the possible switching positions. For example, a "3/2" valve corresponds to three ports and two switching positions. In addition to the different functions of ports and switching positions, the mechanical design and functional design of directional control valves are also different. DCV design types include: plug (spherical plug, flat plug), valve shaft, flat slider and rotary slider. Even within the same type, it is still possible to apply different design methods and materials. For example, a spool valve may have a seal ring along its valve shaft or instead be located in the valve body. Design characteristics affect valve service life, flow rate, actuator, drive force, size, and price.
- When a directional valve is used to perform all switching operations, a Proportional Valve (PV) regulates pressure and flow rate. The main basic characteristic of a proportional valve is to convert an input signal into a specific output signal. Proportional valves usually include two components-a pilot control and a valve unit. The steering control consists of two 2 / 2-way pilot valves or a proportional solenoid (solenoid), and also includes electronic circuits for evaluation. The valve unit only contains integrated pneumatic functions.
- A DC voltage or current (such as 0 ~ 10V voltage or 0 ~ 20mA current) acts on the control block connection. The voltage or current then corresponds to a specific controlled pressure. The actual pressure at the working port is measured by the integrated pressure sensor and sent to the evaluation electronics, which compares the actual pressure to the expected pressure. The electronic circuit unit then sequentially switches the operating position of the pilot valve and the main valve according to the pressure deviation until the desired pressure is obtained. For "standard" directional control valves, there can only be a single switching position, but proportional directional control valves also allow intermediate positions. This means that, for example, in addition to the end positions such as "open" or "closed", intermediate positions such as "slightly open" are possible.
- The actuator used to switch the working position is a proportional electromagnetic coil. When the electromagnetic coil is excited by the electronic circuit, the coil voltage will change accordingly, and the position of the control piston will change according to the changed electromagnetic field strength. As a result, with the help of the control piston, each air passage can be opened or closed to different degrees at the same time. This not only activates open-loop or closed-loop control of the cylinder's movement direction, but also controls the movement speed of the cylinder. Therefore, it can be considered that this valve plays a throttling function. When the switching frequency is about 100 Hz, this type of valve can achieve a relatively high dynamic performance.
- Proportional valves have a wide range of applications. For example, when the material is unrolled, the application of the proportional valve can pneumatically maintain a constant tension during the unwinding process. Proportional directional control valves have further applications in cylinder positioning. In this case, the cylinder is equipped with a displacement encoder that provides a feedback signal of the actual position of the piston. In order to obtain a specific position, a proportional directional control valve controls the volume flow into or out of the cylinder.
- In mechanical operation, the pneumatic valve plays a vital role. It must be used not only with high technical skills, but also with quality assurance. This requires the necessary maintenance and maintenance of the pneumatic valve. Treating with a scientific attitude can make valve maintenance work achieve its due effect and application purpose.
- Precautions for routine maintenance of pneumatic valves:
- 1. The valve should be stored in a dry and ventilated room, and both ends of the passage must be blocked.
- 2. Valves that have been stored for a long time should be checked regularly to remove dirt and coated with rust-proof oil on the processing surface.
- 3. After installation, it should be inspected regularly. The main inspection items are: (1) Wear of sealing surface. (2) Wear of trapezoidal threads on the stem and stem nut. (3) Whether the packing is out of date and should be replaced in time if damaged. (4) After the valve is overhauled and assembled, the sealing performance test shall be performed.
- Precautions for use and maintenance of pneumatic valves:
- 1. The purpose of use and maintenance is to extend valve life and ensure reliable opening and closing.
- 2. The valve stem thread often rubs against the valve stem nut. It should be coated with a little yellow dry oil, molybdenum disulfide or graphite powder for lubrication.
- 3. For valves that do not open and close frequently, you must turn the handwheel regularly to add lubricant to the valve stem threads to prevent biting.
- 4. For outdoor valves, protect the valve stem to prevent rain, snow, dust and rust.
- 5. If the valve is mechanical, please add lubricant to the gearbox on time.
- 6. Always keep the valve clean.
- 7. Always check and maintain the integrity of other parts of the valve. If the fixing nut of the handwheel falls off, it must be matched and cannot be used together, otherwise the four sides of the upper part of the valve stem will be ground, gradually losing the reliability of cooperation, and even unable to start.
- 8. Do not rely on the valve to support other heavy objects. Do not stand on the valve.
- 9. The valve stem, especially the threaded part, should be wiped frequently, and the lubricant that has been contaminated by dust must be replaced with a new one, because the dust contains hard debris, which easily wears the threads and the surface of the valve stem, which affects the service life of the pneumatic unit. Seat regulating valve
- D671- (16, 25) C, P, R, V series wafer type butterfly valve
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