Pneumatic control valve from the basic principle, assembly, maintenance is worth having valve expertise: pneumatic control valve working principle detailed description

Pneumatic control valve from the basic principle, assembly, maintenance is worth having valve expertise: pneumatic control valve working principle detailed description

Pneumatic control valve is one of the industrial process control panels used by crude oil, chemical plant, electric power engineering, metallurgical industry and other manufacturing enterprises. The regulating valve in the chemical enterprise is indispensable in the regulation mode, which is an important part of the industrial production automation technology, such as the hands and feet of the production process automation. Below, take you together to understand the pneumatic control valve.
Pneumatic control valve is one of the industrial process control panels used by crude oil, chemical plant, electric power engineering, metallurgical industry and other manufacturing enterprises. The regulating valve in the chemical enterprise is indispensable in the regulation mode, which is an important part of the industrial production automation technology, such as the hands and feet of the production process automation. Below, take you together to understand the pneumatic control valve.
principle
Pneumatic regulating valve is mainly based on compressed gas as a power device, to the cylinder as a pneumatic actuator, and with the help of electrical equipment valve positioner, converter, relay, retaining valve and other accessories to promote the valve, to achieve switching signal or proportional control, to accept the control instructions of industrial production automatic control system to complete the adjustment of the pipeline medium: Total flow, working pressure, temperature and other technical indicators. Pneumatic control valve is characterized by easy operation, rapid response, and safety system, no need to use explosion-proof devices in addition.
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Principle of pneumatic regulating valve
Pneumatic regulating valve is generally composed of pneumatic actuator and regulating valve connection equipment installation and debugging, pneumatic actuator can be divided into single function or double effect type two, single function actuator has a rectangular spring, and double function actuator has no rectangular spring. Among the single function actuator, from the loss of source or sudden failure, automatic return to the valve originally set open or shut down state.
Pneumatic regulating valve according to the form of action divided into two types of gas open type gas closed type, the so-called normally open type and normally open and normally closed type, pneumatic regulating valve gas open or gas closed, generally by the double-sided effect of the actuator and valve structure is not the same assembly method to complete.
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Pneumatic regulating valve action mechanism
Gas open type (normally open and normally closed type) when the gas pressure on the top of the membrane is raised, the valve is increased to the opening degree position. When the standard pressure limit is reached, the valve is in the open state. In contrast, when the gas pressure is reduced, the valve is positioned in the closed position, and when no gas is entered, the valve is fully closed. Gu generally called the gas open type regulator for the problem off type valve.
Gas close type (normally open type) operating orientation and gas open type just reverse. When the gas pressure rises, the valve to close position; When the gas pressure is reduced or not, the valve should be opened to the open direction or open. In general, we call the gas closed type regulator open type valve for common failures.
The choice of gas opening and closing is based on the safety of manufacturing process. When the air source is disconnected, the regulating valve is in the closed part of the safety or open part of the safety.
For example, the combustion control of a heat treatment furnace, the regulating valve installed in the fuel gas pipeline, according to the temperature in the furnace or the temperature of the heated material at the inlet and outlet of the heat treatment furnace to adjust the material market supply. At this time, the safety factor of the gas opening valve should be selected, because once the gas source is terminated, the valve is closed than the valve is opened. If the air source is eventually broken and the energy valve is opened, it will allow excessive heating to occur. Also like a thermal equipment refrigeration with cooling circulating water, the hot material in the heat exchanger and cooling circulating water heat exchanger is refrigerated, the regulating valve is installed on the cooling pipe, with the heat exchange material temperature to control the flow of cooling water, in the end of the air source, the regulating valve should be in the position of the safety factor is higher, should choose to use the gas close type (FO) regulating valve.
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Valve positioner
Valve positioner is an important part of the control valve, with the pneumatic control valve, it receives the pulse signal of the controller, and with its pulse signal to control the pneumatic control valve, when the control valve position, stem offset also through the electronic device feedback to the valve positioner, valve position according to the electronic signal sent to the stage system software. Valve positioner according to its structure and principle can be divided into pneumatic valve positioner, electric-gas valve positioner intelligent valve positioner.
Valve positioner can expand the power of the regulating valve, reduce the power transmission of the adjustment signal, accelerate the speed of the valve stem, can improve the linear valve, get rid of the friction of the valve stem and remove the influence of the unbalanced force, fully ensure the correct and accurate positioning of the regulating valve.
Pneumatic actuator, electric actuator, direct travel arrangement, Angle travel arrangement difference. Used for automatic and manual opening and closing all kinds of doors, fans, etc.
Assembly standard for pneumatic regulating valves
(1) pneumatic control valve installation, there is a certain relative height from the ground, the valve to leave a certain space, easy to carry out the valve disassembly and maintenance. For regulating valves equipped with pneumatic valve positioner and spindle, it is necessary to ensure practical operation, careful observation and convenient adjustment.
(2) The regulating valve should be set in the leveling pipe, and about and vertical pipe, generally under the valve for its support point, to ensure that firmly reliable. For unique occasions, it is necessary to install the valve level in the vertical pipeline somewhere, should also be the first control valve to carry out support point (outside the diameter of the valve). Installation, must avoid additional stress to the regulating valve).
(3) The working temperature of the regulating valve needs to be in (-30 ~ 60) air humidity shall not exceed 95%95%, air humidity shall not exceed 95%.
(4) The regulating valve before and after the left and right parts should have a straight pipe section, the length is not less than 10 times the pipe size (10D), in order to prevent the valve of the straight pipe section is too short to affect the flow coefficient.
(5) When the specifications of the regulating valve and the process pipeline are different, eccentric reducing pipe should be used for connection. In the calibre regulating valve installation, can use flange connection. The liquid indicating arrow on the oil circuit board shall be in the same direction as the liquid.
(6) To set bypass pipeline. The purpose is to facilitate conversion or manual control without maintenance of the regulator in parking condition.
(7) Regulating valve in the pipeline before the construction of a comprehensive dirty things, such as stains, welding scars, etc.
Common problems and solutions
The regulator is not in position
First determine whether there is a problem with the working pressure of the air source, search for common faults of the air source. If the working pressure of the air source is normal, distinguish whether the amplifier circuit of the locator or the electric/gas converter is derived; If there is no export, the amplifier constant throttle hole is blocked, or the air concentration in the amplifier gate valve is reduced. Use fine wire to feed through the constant throttle hole, waste or clean up the air source.
If the above are normal, there is no posture if there is data signal, then the actuator is commonly faulty or the valve stem is bent, or the valve core is stuck. In this case, be sure to remove the valve for further inspection.
The regulating valve is stuck
If the reciprocating stroke arrangement of the valve stem posture is slow, the valve body or a little more viscous chemicals, scaling blocking or filling material pressed tight, or PTFE filling material aging, stem bending scratch. Most of the control valve jam problems occur into the new use of software and maintenance in the early stage, because in the pipeline welding scar, rust in the throttle valve port and conductive position lead to blocking so that the flow of material goods blocked, or control valve maintenance filling material is too tight, resulting in the expansion of sliding friction, resulting in small signal posture, big data signal posture is excessive.
In such cases, you can quickly open and close the auxiliary line should regulate the valve, so that the garbage from the auxiliary line should be run by the material. In addition, the pipe clamp can also be used to hold the valve stem, in addition to the data signal working pressure situation, double-sided force to rotate the valve stem, so that the valve core flash out of the card. If you can’t deal with the problem, you can increase the working pressure of the air source and increase the driving power to move up and down for several times. Then you can deal with the problem. If it is still unable to posture, it is necessary to disassemble the pressure regulating valve. Naturally, this work requires strong professional ability and must be carried out with the help of professional technology, otherwise the adverse effects are more serious.