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Keywords: Pneumatic Regulating Valves, Installation, Maintenance, New Concepts Shannon Pneumatic Regulating Valves mainly include Pneumatic Straight-travel Regulating Valves, Pneumatic Rotary Regulating Valves, Pneumatic Straight-travel Shut-Off Valves, and Gas (Liquid) Dynamic Angled Travel Shutoff Valves. Their correct installation is just as important as the right choice. The quality of the installation is a top priority related to operational performance, safety, and cost. The regulating valve must be installed strictly in accordance with the process requirements and the control system requirements. Once the valve fails, it will result in serious accidents such as fire, explosion, poisoning and personal injury. The loss cannot be calculated. Therefore, we cannot take it lightly.
1. Inspection before Installation Before installing the regulating valve, check the product quality of the regulating valve. Start with the visual inspection. Then check whether the parts and accessories are lost during transportation, whether there is certificate of conformity, and check the static characteristics if necessary. Special inspection.
2. Installation Principles (1) The installation position of the pneumatic control valve requires a certain height from the ground. There must be space above and below the valve for the disassembly and repair of the valve. For regulating valves equipped with pneumatic valve positioners and handwheels, operation, observation and adjustment must be ensured.
(2) The regulating valve should be installed on the horizontal pipeline and up and down the pipeline. It should be supported under the valve to ensure stability and reliability. For special occasions, when the regulator valve needs to be installed horizontally on a vertical pipe, the regulator valve should also be supported (except for the small-diameter regulator valve). When installing, it is necessary to avoid additional stress on the regulating valve, such as the pipe and valve are not concentric or the flange is not parallel.
(3) The working ambient temperature of the valve should be at (-30 ~ +60) °C and relative humidity should not exceed 95%. Because rubber parts such as membranes and seal rings of regulating valves are easy to be hardened and brittle at a low temperature and aged at a high temperature, installation positions should be paid attention to during installation, and heating furnaces and high-temperature pipes should be left.
(4) There should be a straight pipe section in the forward and backward position of the valve, and the length of the pipe that is not less than 10 times the straight pipe length before and after the valve (10D) to prevent the straight pipe section of the valve from being too short and affecting the flow characteristics.
(5) When the diameter of the regulating valve is different from the process piping, the different-diameter pipe connection should be adopted. When the small diameter control valve is installed, it can be threaded. The fluid direction arrow on the valve body should be consistent with the fluid direction.
(6) Set bypass piping. The purpose is to facilitate switching or manual operation, and the valve can be serviced without stopping.
(7) Before the installation of the regulating valve, it is necessary to completely remove the foreign matter in the pipeline, such as dirt, welding slag and so on. After installation, the test run is performed with normal temperature water. During the test run, the valve shall be fully opened or the bypass valve shall be opened. During the test run, attention should be paid to the sealing of the connection between the valve body and the pipe.
3, installation of the form of control valve installation There is usually a control valve group, namely the upstream valve, bypass valve, downstream valve and regulating valve. Figure 1 shows the six combinations commonly used for regulating valves. It should be noted that the shut-off valve (upstream valve, downstream valve) and the bypass valve should be installed close to the tee to reduce the dead angle.
4, the choice of control valve installation position usually adjust the valve requires vertical installation. In the case of vertical installation, the four-bolt adjustable valve for the flange may have four positions: upward tilting 45°, downward tilting 45°, horizontal mounting, and vertical downward mounting. For the flange with 8 bolts of the regulator valve can have 9 installation positions, respectively, separated by 22.5 °.
In these installation positions, the most ideal is to install vertically upwards, which should be preferred; the upwardly inclined position is secondarily followed by 22.5°, 45°, and 67.5°; the downward vertical installation is the re-position; the worst position is horizontal For installation, it is inclined to 67.5° with a nearly horizontal installation, generally not adopted. Figure 8-4 shows a comparison diagram of the installation position.
5. Maintenance of Regulating Valves Due to the harsh environment in which the regulating valves are used, it is inevitable that certain malfunctions will occur during use. Therefore, it is necessary to perform certain maintenance and maintenance of the regulating valve. The main contents of daily maintenance of pneumatic control valve should have the following items:
(1) Valve body wall. Check its pressure and corrosion resistance.
(2) Seat. Due to medium infiltration, the inner surface of the thread used to fix the valve seat is susceptible to corrosion and the valve seat is loosened. Care should be taken during inspection. For high pressure applications, also check that the valve seat sealing surface is damaged.
(3) Spool. It is necessary to carefully inspect whether the various parts of the spool are corroded and worn, especially if the spool wears more seriously under high differential pressure, and care should be taken. In addition, it should also check whether the stem has a similar phenomenon, or loose connection with the spool.
(4) Diaphragms, o-rings, and other seals. Check for aging and cracking.
(5) Sealing packing. Check whether the PTFE packing, seal grease is aging, dry, and whether the mating surface is damaged. Table 1 shows the common faults and main causes of pneumatic control valves for reference when using them.
Common Causes of Main Causes of Malfunction The valve does not operate The positioner has airflow, but there is no output 1 Blocking of the constant orifice in the amplifier of the positioner 2 Moisture in the compressed air Accumulated at the ball of the amplifier Signal surface No action 1 Spool and bushing or valve Seat stuck 2 Spool off 3 Stem bent or broken 4 Actuator malfunction Valve movement is unstable Air source signal pressure is constant, but valve action is still unstable 1 Positioner is defective 2 Output line leak 3 Actuator stiffness too Small, insufficient pressure caused by changes in liquid pressure. 4 Valve friction. Large valve shakes and slamming. When the valve closes to the fully closed position. Vibration 1 The control valve is selected large, often when the small opening is used. 2 The flow direction of the medium is the same as the valve closing direction. The valve is vibrated at any degree of opening. 1 The support is unstable. 2 The vibration source near the 3 valve plug and the bushing wear valve are dull. The reciprocating stroke of the valve stem is unresponsive. 1 The valve body has mud or viscous medium, and it is clogged or coke. PTFE packing Hardened and degraded Stem Slow motion in one direction Action 1 Corrugated film breakage in air chamber 2 Air leak in chamber Air leak in valve 1 Corrosion and wear of the valve plug or valve seat 2 The thread of the outer circle of the valve seat is corroded and the valve cannot reach the fully closed position. 1 The medium pressure difference is too large. The actuator output force is not enough. 2 The foreign body in the valve body is filled with foreign matter and the connection leaks. Leakage 1 Packing gland not pressed 2 PTFE packing aging deterioration 3 Stem damage Valve body and upper and lower bonnet joint leakage 1 Hex nut tightening loose 2 Damage to gasket 6. Regulator valve installation and maintenance new concept The current industrial process automation technology has changed greatly compared with the situation 20 years ago. The main difference lies in the emergence of smart devices. It is equipped with a high-speed communication bus, which can easily provide a large number of factory monitoring centers. Information, for superior leadership and departmental decision making, is something that could not be achieved in the past. However, it is regrettable that most of the basic automated pneumatic valve kits currently installed do not keep pace with the rapid intelligence and high-speed communications. Most of the valves still use purely mechanical discrete monitoring methods. The degree of intelligence is low or not even, which brings certain difficulties to the installation and maintenance of the regulating valve, and reduces the quality of installation and maintenance and the working efficiency.
The new concept of control valve installation and maintenance is to apply sensor, intelligent and computer information technology in the control valve products, and to develop intelligent, networked pneumatic control valves, to pass control valve installation position, working status and other information through industrial Ethernet. Real-time transmission to the control command center, on-line dynamic management of the regulating valve, timely maintenance, not only guarantees the working quality of the regulating valve, but also improves work efficiency. In short, the development of intelligent, networked, maintenance-free regulating valves is the development direction of industrial process automation.
Pneumatic regulating valve installation and maintenance
Abstract: This article discusses the main points of the installation and maintenance of the regulating valve from the aspects of inspection, installation principle, installation form, selection of installation orientation and maintenance of the regulating valve before the installation of the pneumatic regulating valve. It is pointed out that in the information age, the installation of the pneumatic safety valve and The new concept of maintenance is to vigorously develop intelligent, network-based new control valves, improve installation and maintenance efficiency, and strengthen online real-time monitoring of control valves.