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Talking about the installation and commissioning of regulating valve

Writer:CondiDate:2017-2-23 09:46
 
With the advancement of science and technology, the control valves used to control fluid flow in the production process automation have been widely used in various industries. For the thermodynamic and chemical control system, as the final control process of the quality of the media and safety indicators of the control valve, in the stable production, optimization control, maintenance and maintenance costs play a pivotal role. In the application of the control valve, the calculation and selection is the premise, installation and commissioning is the key, use and maintenance is the purpose. If the valve is not properly installed, or debugging is not good, it can not achieve the role of regulation, and even become a cumbersome system.
    1, the installation of the control valve
    1.1 The basic principles of installation
    The installation of the control valve should follow the relevant national standards, in accordance with the provisions of the design drawings and design documents strictly enforced. For example, the construction and installation engineering quality inspection and evaluation standards, industrial automation instrument construction and acceptance norms, electrical equipment installation engineering construction and acceptance specifications; installation of the necessary equipment, auxiliary equipment and main materials should be consistent with the relevant provisions of the existing national standards.
    1.2 Inspection before installation
    Control valves and accessories from the factory to the installation before the transport by the transport tool to stimulate the random vibration and loading and unloading by the various shocks, as well as in the transport and storage process, the environment temperature, humidity and other changes, which may cause The performance of the control valve and accessories changes. Therefore, it is necessary to perform part of the performance test before installation.
    The inspection of the control valve before installation includes the following: appearance, static characteristics, leakage, no-load full stroke time, pressure strength, insulation performance, air tightness and sealing, etc., of which the first five items for the inspection. Of course, there are certain requirements for the place of inspection. For example: the ambient temperature requirements in the 10 ~ 35 ℃; air relative humidity of not more than 75%; the venue has enough space, and the light is sufficient or lighting conditions; around can not have a strong vibration and strong magnetic field interference; Requirements and so on.
    1.3 Installation Precautions
    The installation of the control valve must ensure safety, ensure performance, ease of operation and maintenance, and save installation costs. The following four points on the installation of the need to pay attention to the specific issues.
    1.3.1 to ensure security
    1) to prevent leakage
    The installation process does not allow the control valve to leak. In the course of the use, if the filler culvert, flange gasket and other parts of the gap or micropores may produce leakage. If the operating conditions of the fluid medium are harsh, such as high temperature, high pressure, fluid corrosion, then the damage will intensify, the greater the risk of leakage. There are many ways to prevent leakage, in the installation process, the choice of filler, the choice of sealing method, the choice of good sealing performance valve, etc., must be considered factors.
    2) Install the drain valve
    Any pipeline design and installation, in the cut off when the inevitable accumulation of high-pressure fluid, if the potential energy accumulation of fluid, should be installed on both sides of the valve release valve, so that after the system cut off, the control valve In the residual high-pressure fluid energy can be released to protect the safety of personnel, is conducive to the maintenance of the valve, you can also consider the use of discharge can limit the discharge valve.
    3) safe pipelines
    Before installing the regulating valve, all the installation of pipe and pipe should be cleaned, because the pipeline in the sand, scale, iron, etc. will damage the inner surface of the valve, in particular, requires a strict sealing surface. When the system pressure is severe, it is recommended to install a buffer facility on the pipeline. If the discharged fluid is a hazardous gas or liquid, the piping for the discharge of the fluid must be connected to a safe location or to a safe, specific container, which protects the person from injury without causing pollution to the environment.
    1.3.2 to ensure the use of performance
    When installing the control valve, try to ensure that its performance is not affected. This effect will destroy the various factors considered when selecting the control valve.
    1) Installation of the upper and lower shut-off valves and bypass valves
    The length of the straight pipe between the upper and lower shut-off valve and the regulator should take into account the resistance of the pipe and the effect on the fluid flow. Straight pipe length is long, is conducive to the stability of the fluid after the cut off the valve, the fluid flow can be smooth to reduce the impact of turbulence, reduce noise; straight pipe length is short, the fluid has not yet stabilized after the valve into the control valve, Large, but the length of the straight pipe is short to help reduce the pipeline resistance, improve the pressure drop across the control valve, the flow characteristics of the distortion is reduced, is conducive to the stable operation of the control system. Therefore, we should weigh the pros and cons, consider. According to experience, usually on the upstream side should have 10D ~ 20D straight pipe, the downstream side of the 3D ~ 5D straight pipe (D for the pipe diameter), if necessary, should be set up rectifier device.
    When the valve is disassembled and repaired, the bypass valve can be used to operate the production process. When the controlled flow is too large, with the control valve can not be properly adjusted, as a contingency measure, bypass valve can also be used as a control valve parallel connection program, the process control. To reduce costs, large diameter control valve installation hand wheel actuator, can replace the bypass valve to operate. The installation of the bypass valve should be easy to operate, with the control valve and the upper and lower shut-off valve together to form the control valve group. Therefore, when installing the control valve should be combined with the shut-off valve and bypass valve to consider, and at the same time to complete the construction and installation. The nominal diameter of the bypass valve is the same as the nominal diameter of the pipe, and the pressure rating is also consistent with the process pressure rating.
    2) the installation of the bleed valve, vent valve and drain valve
    In order to facilitate the disassembly of the control valve, before the demolition must be carried out before the valve and the valve after the release of pressure, relief valve should be installed in the control valve and the upstream and downstream shut off valve. The vent valve and the drain valve are used to discharge the non-condensable gas and condensate entrained in the fluid. If the controlled fluid is gas or steam at the time of installation, the discharge valve should be installed at the lowest point of the regulating valve group in order to facilitate the discharge of the condensate. When the controlled fluid is liquid, in order to facilitate the discharge of non-condensable gas, venting valve should be installed in the highest control valve group.
    3) Connection of regulating valve to pipe
    The connection between the regulating valve and the pipe is the difference between the screw connection, the flange connection and the welding connection. Threaded connection for the installation of small diameter valve, you must also install the removable movable connector; flange connection with ordinary flange connection and clamping type of two, pipe connecting flange nominal diameter should be adjusted Valve diameter consistent with the pressure level should also be consistent with the pressure level of the control valve, flange surface and the vertical axis of the pipeline to allow the deviation of l °; try to avoid the use of welding connection. When the valve is connected, a new protrusion should not be present inside the connecting pipe. For example, the gasket, weld seam, etc. should not protrude in the pipe. At the same time, it should be noted that the flow of fluid in the regulating valve should be consistent with the direction of the arrow marked on the valve body, under special circumstances can not be limited.
    4) Installation of the implementing agency
    In general, the actuator is connected directly with the valve body of the control valve. However, when the hydraulic actuator, the long stroke actuator and the like are separated from the valve body, it is important to note that the connecting rod and the mechanical moving parts of the actuator should be flexible and Loose or stuck and other phenomena; connecting rod length appropriate to ensure that the whole range of action within the stable, flexible and reliable; hand wheel executive body side mounted and top two, the installation should be left to operate the space, hand wheel operation should be flexible , There is no stuck or twist phenomenon, there are hand wheel rotation direction and the valve opening relationship between the label, the limit device should be adjusted to play a protective role; hydraulic actuator should be lower than the controller installation, if it must be higher than the controller Installation, the height difference should not exceed 1.0m, and should be installed in the pipeline gas collection valve, close to the controller installed automatic shut off valve.
    5) Installation of the valve positioner
    Valve positioner valve position detection device and the valve stem or valve shaft directly connected, therefore, the installation should ensure that the feedback signal can correctly and timely reflect the valve position signal and change. Typically, the valve positioner is supplied with the control valve, and the connection is made by the manufacturer. When the production process control need to add the valve positioner, should ensure that the valve positioner valve position detection device action is correct, reliable and flexible, the feedback shaft fulcrum of the mechanical gap should be as small as possible, the valve positioner signal pipeline should be properly connected, Pipeline and output lines, the input line should be marked; valve positioner valve position display signal should be conducive to the operation and maintenance personnel observation.
 
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