Pneumatic control valve selection and precautions

- Sep 23, 2019-

What are the classifications of pneumatic control valves? How do they distinguish between choices? Of course, this is a certain data to choose from, such as small mouth small meteor to choose a single seat regulating valve, large diameter large meteor to select the sleeve regulating valve, the return system to select the three-way diverter valve. The adjustment structure is actually very simple, it is divided into two-way and three-way. As for the single seat and the sleeve, this is selected according to the flow size. The user only needs to know the selection process during the selection process. The detailed core technology is to pass the professional The structure and caliber of software and computational formula technology. The following table is the classification of Taichen regulating valve for reference. The actual application should provide. The technical documents such as pressure, flow, medium and temperature of the valve before the valve are calculated by professional techniques to meet the actual situation.


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Selection of pneumatic control valve

First, about the valve body

1. In the case of constant pressure difference, the top-guide type one-way regulating valve with unbalanced fluid pressure is a single-seat regulating valve with small size and simple structure, but it can adapt to harsh working conditions. Due to the use of an unbalanced spool, the combination is compacted with a small, multi-spring diaphragm actuator. This series of regulating valves is particularly suitable for a wide range of fluids due to the absence of a fluid pressure balancing structure.


2. Double seat control valve is used for high pressure and high pressure difference. However, if the leakage of the valve seat is relatively high, the sleeve single seat control valve should be used.


3. When the noise of the regulating system to the regulating valve is greater than 85 decibels, the noise reduction regulating valve should be selected.


4. For the case of low pressure and large flow range, an adjustable ball valve should be used.


5. The valve that is more serious in fluid flushing or working in the flash needle state is indented in principle, and the valve core and the valve seat are all surfacing with the Stellite alloy.


6. For the control valve working under strong acid and alkali medium, anti-corrosion measures should be taken. For example, corrosion-resistant stainless steel or the body is made of all-lined PTFE to achieve anti-corrosion. All valves and actuators are sandblasted and all bolts and nuts are corrosion resistant for use in Xinjiang.


7. The material and pressure rating of the valve body, trim and seal of the regulating valve shall comply with the process conditions of the installation and the environmental requirements of the site. The regulating valve has a local mechanical indicating device that can indicate the opening of the valve in place.


8. Matching pipe fittings and supporting flanges, nuts (120%), nuts (120%), gaskets (200%). The mating flange material must be exactly the same as the process pipe material to facilitate welding during on-site construction.


9. Signs and nameplates Each valve has a stainless steel nameplate. The nameplate should be in an easy-to-see position. The nameplate should contain the following.


1) Name of the manufacturing plant


2) Valve's serial number, manufacturing number and model number


3) Material, size and pressure rating of the valve body


The selection of the regulating valve should be based on the media, flow, pressure, temperature, viscosity, process diameter and other parameters after the valve is issued. It is calculated by the original manufacturer's original software and fully meets the design requirements.


Second, about the actuator

1. For the selection of actuators, the general type of actuators can be selected for the southern regions of China, and the low-temperature actuators must be used for the cold regions in the north. The regulator actuator should use a high temperature actuator. The actuator used is of low temperature type, the connecting bracket is made of low temperature resistant cast steel, the rubber parts such as diaphragm and 0 type ring are made of low temperature resistant material, and the lubrication grease is also resistant to low temperature grease.


2. The actuator is currently used as a multi-spring structure, which is characterized by light weight, small size, high performance and large output force. The pneumatic actuator is matched with the type and size of the selected regulating valve. For the large diameter regulating valve, a multi-spring film structure is selected.


Third, on the attachment

1. The electric valve positioner should receive the analog signal of 4~20mADC, and the power supply voltage is 24VDC. The basic error is ≤±0.1%; the insensitive area fine-tuning range: 0.3~10%; gas consumption: “3NL/min (not related to the supply pressure).


2. The positioner is the soul and heart of the whole regulating valve, which directly affects the reliability of the regulating valve. In principle, the positioner should be imported as much as possible when selecting the regulating valve. At the same time, for different regions, the ordinary type, high temperature type and low temperature type should be selected separately.


3. The electric valve positioner, pneumatic actuator and air filter pressure reducing valve of the regulating valve are used as an integral part of the regulating valve. The assembly kit is supplied to the owner and assembled by the factory before the regulating valve is delivered. Qualified testing of all functions.


4. The filter pressure reducing valve should be selected according to the size of the actuators equipped with the regulating valve to meet the gas supply requirements. According to the working environment, it is divided into normal temperature type, high temperature type and low temperature type.


5. All electrical parts of the positioner should meet the requirements of the on-site protection level.


Pneumatic control valve selection considerations

1. Defining the use of the pneumatic regulating valve in the equipment or device, and determining the working conditions of the pneumatic regulating valve: applicable medium, working pressure, working temperature, and the like.


2. Determine the nominal diameter and connection method of the pipe connected to the pneumatic control valve: flange, thread, welding, etc.


3. Determine the type of pneumatic regulating valve: gate valve, globe valve, ball valve, butterfly valve, throttle valve, safety valve, pressure reducing valve, steam trap, etc.


4, determine the action mode can be divided into: straight stroke and angular stroke two ways.


5. Select the type of pneumatic regulating valve: closed-circuit pneumatic regulating valve, adjusting pneumatic regulating valve, safety pneumatic regulating valve, etc.


6. Determine the parameters of the pneumatic regulating valve: For the automatic pneumatic regulating valve, determine the allowable flow resistance, discharge capacity, back pressure, etc. according to different needs, and then determine the nominal diameter of the pipe and the diameter of the seat hole.


7. Determine the way to operate the pneumatic control valve: manual, electric, electromagnetic, pneumatic or hydraulic, electrical linkage or electro-hydraulic linkage.


8. Determine the material of the housing and internal parts of the selected pneumatic regulating valve according to the medium, working pressure and working temperature delivered by the pipeline: gray cast iron, malleable cast iron, ductile iron, carbon steel, alloy steel, stainless acid-resistant steel, copper alloy Wait.


9. Finalize the precautions for use.