Selection and installation of pneumatic control valves

1. The top-guided check valve with unbalanced fluid pressure is a single-seat control valve with a small volume and simple structure that can adapt to harsh working conditions for applications with normal differential pressure. Due to the use of unbalanced spool, and compact design of the multi-spring membrane actuator combination, the appearance is greatly reduced. Since there is no fluid pressure balance structure, this series of control valves is particularly suitable for a variety of fluids.
2. high-pressure and high-pressure differential occasions to use double-seat control valve, but if the seat of the valve leakage requirements are relatively high to use sleeve single-seat control valve.
3. when the noise of the regulating system on the regulating valve is greater than 85 decibels should be used to reduce the noise of the regulating valve.
4. for lower pressure, flow range of occasions should choose adjustable ball valves.
5. on the more serious fluid scouring or work in the flash needle state of the valve is used in principle indentation, spool, seat all with Staley alloy surfacing.
6. for the strong acid and alkali media working under the regulating valve to take corrosion-resistant measures, such as the selection of corrosion-resistant stainless steel or method of body using all lined with PTFE in order to achieve the purpose of corrosion prevention. All valves and actuators are used to prevent sand spraying, all bolts and nuts with corrosion-resistant outer layer.
7. the valve body, valve components and seals of the material and pressure resistance level should be in line with the installation of the process conditions and environmental requirements of the site. Control valve with on-site mechanical indication device, can locally indicate the valve opening.
8. control valve piping connector and matching flange, nut (120%), nut (120%), gasket (200%) matching. Matching flange material must be exactly the same with the process piping material, to facilitate on-site construction process welding.
9. signs and nameplates each valve has a stainless steel nameplate, the nameplate should be in an easy to observe position, the nameplate should contain the following content.
   1. the name of the manufacturer
   2. the valve's bit number, manufacturing number and model number
   3. Valve body material, size, pressure level

Control valve selection should be based on the site to provide the medium, flow, valve issued after the pressure, temperature, viscosity, process pipe diameter and other parameters, after the original manufacturer of the original software calculations, and fully comply with the design requirements.

1. for the selection of the actuator should be for the climate, conditions, low latitude areas can choose ordinary type of actuator, but for high latitude and high temperature areas must choose low-temperature type of actuator, for the ambient temperature for a long time in the high temperature of the valve actuator should be selected high temperature type of actuator. The actuator used for low-temperature type, its connection bracket selection of low-temperature-resistant cast steel, diaphragm, 0-ring and other rubber parts are used for low-temperature-resistant materials, lubrication grease with low-temperature-resistant lubricating grease.
2. the actuator is currently used for the multi-spring structure, which is characterized by light weight, small size, high performance, large output force. Pneumatic actuators and the selected type of control valve, size and other matching; for large diameter control valves, the choice of multi-spring membrane structure.

1. electrical valve positioner should receive 4 ~ 20mADC analog signal, power supply voltage 24VDC, basic error ≤ ± 0.1%; insensitive area fine-tuning range: 0.3 ~ 10%; gas consumption: <3NL/min (independent of gas supply pressure).
2. the positioner is the soul and heart of the entire regulating valve, directly affecting the reliability of the regulating valve, in principle, in the selection of regulating valve positioner try to use imported original. At the same time, for different areas to be selected for ordinary, high temperature type and low temperature type.
3. the regulator valve electrical valve positioner, pneumatic actuators, air filtering pressure reducing valve as a component of the regulator valve, supporting the work, to the owner of a unified supply, and in the regulator valve before shipment by the factory assembly and qualified testing of all functions.
4. filtering pressure reducing valve selection according to the size of the control valve with the actuator to meet the requirements of the air supply. According to the working environment is divided into normal temperature type, high temperature type and low temperature type.
5. All electrical parts of the positioner should be able to meet the requirements of field protection level.

1. in order to ensure the safety and reliability of the work of the control valve, should try to use the horizontal installation, before and after the valve to ensure that the length of the straight pipe section of 10D, should be avoided in the vibration intensity of the occasions installed. Such as the pump outlet location to try to extend the pipeline approach to avoid damage to the control valve.
2. to ensure that the control valve and process piping in the same straight line, while keeping the actuator vertical.
3. Bolts should be double head bolts. The gasket should use the metal wound gasket which can be reused many times to ensure the sealing reliability of the regulating valve.
4. to ensure that the regulating valve in the future use of adequate maintenance space. General control valve are equipped with a negative line, in the section of the valve can be switched to the negative line in case of emergency, but in the installation of the negative line is to pay attention to the control valve to leave a certain amount of maintenance space, generally not less than 50CM distance.
5. replace the valve core, valve seat. For the regulating valve with handwheel mechanism, turn the handwheel mechanism to the limit position, use the special hexagonal wrench to loosen the cross connection block of the regulating valve actuator and spool, so that the actuator and the spool connection is disengaged. Loosen the screws of the upper valve cover and take down the whole upper valve cover together with the actuator. You can use a special tool to replace the spool valve seat respectively, and then replace the new spool valve seat can be.
6. replace the actuator: the installation should pay attention to is the air tank of the vertical (vertical) or level (bedroom) system. Cylinder up and down must be free, there can be no jamming phenomenon. In order to facilitate maintenance and repair, start the actuator should be installed near the ground or floor. When equipped with valve positioner or the first wheel mechanism should be more to ensure the convenience of observation and adjustment and operation. The function of the first wheel mechanism is: in case of accident, it can be used to operate the control valve directly and manually without pneumatic drive.

The starting actuator should be installed in a place where the ambient temperature is not higher than +60℃ and not lower than -40℃, and should be far away from the equipment with high vibration. In order to avoid heat aging of the diaphragm, the distance between the upper diaphragm cover of the control valve and the heat-carrying pipeline or equipment should be more than 200mm. When the nominal diameter of the valve is different from that of the pipeline, a piece of reducer should be added between the two. The pneumatic actuator should be installed vertically on the horizontal pipeline.

When special circumstances require horizontal or inclined installation, except for small-diameter valves, support should generally be added. Even if the valve is installed upright, it should be supported when it has a large self-weight and vibration.

The direction of the fluid through the control valve is marked on the valve body, and cannot be installed in reverse, just as the orifice plate cannot be installed in reverse.

Control valve before and after the installation of a cut-off valve, in order to repair the control valve removed.

Before the control valve is installed, the piping should be cleaned to remove dirt and weld slag. After installation, the pipeline and valve should also be cleaned again, and check the sealing performance of the valve and pipeline connections. When the medium is initially energized, the valve should be kept in the fully open position to avoid magazine jamming.