Installation og valves
1.1 Maintenance, Installation, and Use Precautions
1) The valve should be placed in a dry and ventilated room, and both ends of the diameter should be sealed to prevent dust; 2) Long term storage should be regularly inspected and oil should be applied to the processing surface to prevent rusting; 3）Before installing the valve, carefully check whether the markings match the usage requirements;
4) During installation, the inner cavity and sealing surface should be cleaned, and the packing should be checked for tightness and the connecting bolts should be evenly tightened;
5) Valves should be installed in the allowed working position, but attention should be paid to the convenience of maintenance and operation;
6) During use, do not partially open the gate valve to adjust the flow rate, in order to avoid damaging the sealing surface when the medium flow rate is high. It is recommended to fully open or fully close it;
7) Rotate the handwheel when opening or closing, and do not use other auxiliary levers;
8) Transmission components should be regularly lubricated with oil; When using the valve, the rotating part should be regularly oiled, and the trapezoidal thread part of the valve stem should be oiled.
9) After installation, regular maintenance should be carried out to remove dirt from the inner cavity, check the sealing surface, and inspect the wear of the valve stem nut;
10) There should be a set of scientifically correct installation and operation standards. Sealing performance tests should be conducted during maintenance, and detailed records should be kept for inspection.
11) Other precautions:
1) Valves should generally be positioned before pipeline installation. The piping should be natural, and if the position is not correct, it cannot be forcefully pulled to avoid leaving prestress;
2) Before positioning, low-temperature valves should undergo opening and closing tests in a cold state (such as in liquid nitrogen) as much as possible, requiring flexibility and no jamming phenomenon;
3) Liquid valves should be configured with a 10 ° inclination angle between the valve stem and the horizontal to prevent liquid from flowing out along the valve stem and increasing cold loss; More importantly, it is necessary to avoid the liquid from touching the sealing surface of the packing, causing it to harden and lose its sealing effect, resulting in leakage;
4) The connection of the safety valve should have an elbow to avoid direct impact on the valve; In addition, it is necessary to ensure that the safety valve does not frost to prevent failure during operation;
5) The installation of the globe valve should ensure that the flow direction of the medium is consistent with the arrow marked on the valve body, so that when the valve is closed, pressure is applied to the cone at the top of the valve, and the packing is not loaded. But for valves that are not frequently opened and closed but require strict assurance of no leakage in the closed state (such as heating valves), they can be consciously reversed to be tightly closed with the help of medium pressure;
6) Large scale gate valves and pneumatic control valves should be installed vertically to avoid tilting towards one side due to the heavy weight of the valve core, which increases mechanical wear between the valve core and the liner and causes leakage;
7) When tightening the compression screw, the valve should be in a slightly open position to avoid damaging the sealing surface of the valve top;
8) After all valves are in place, they should be opened and closed again, and it is qualified if they are flexible and not stuck;
9) After bare cooling, the connecting valve flange of a large air separation tower is pre tightened once in the cold state to prevent leakage at room temperature but at low temperature;
10) It is strictly prohibited to use the valve stem as a scaffold to climb high temperature valves above 200 ℃ during installation. As the installation is at room temperature, after normal use, the temperature rises, the bolts expand due to heat, and the gap increases. Therefore, they must be tightened again, which is called "hot tightening".
11) Operators should pay attention to this work, otherwise leakage may occur.
12) When the weather is cold and the water valve is closed for a long time, the accumulated water behind the valve should be drained.
1.2 Homework System and Homework Site
1.2.1 During construction, the construction contractor, safety department, factory production department, and construction unit should fully coordinate to clarify the scope of work responsibilities.
1.2.2 Full time responsible persons shall work on-site in their respective work responsibility areas.
1.2.3 When dismantling or installing valves, corresponding changes and arrangements should be made to the daily production within a certain range affected by such operations, and the medium in the pipeline should be cleared and cut off.
1.2.4 The necessary work site should be ensured at the work site.
1.2.5 Support components that are compatible with the weight of the valve should be installed at the work site to prevent the valve from sinking and the center of the piping from shifting.
1.2.6 After completing the homework, preparations should be made for inspection items such as pressure resistance test, air tightness test, and non-destructive inspection.
1.2.7 Before entering production operation after completing the homework, the interior of the pipeline network should be cleaned, and it should be confirmed whether the blind plates on the pipeline have been removed, as well as whether the valves operated during construction should be restored to their pre construction open and closed states.
1.3 Precautions for valve installation
1.3.1 Before valve installation, it is necessary to confirm that the valve meets the design requirements and relevant standards. 1.3.2 When handling and installing valves, precautions should be taken to prevent accidents such as collisions and scratches. 1.3.3 Before installing valves, the interior of the pipeline should be cleaned to remove impurities such as iron filings and prevent foreign objects from entering the valve sealing seat. In addition, the valve during installation should be in the closed state.
1.3.4 During valve lifting operations. Valves should be lifted correctly at the designated lifting position, and should not be lifted or pulled only under local stress.
1.3.5When installing valves, it is necessary to confirm whether the flow direction of the medium, installation form, and handwheel position comply with regulations.
1.3.6 Installation of flange connected valves.
1) The flange surfaces of valves and piping should be free of damage, scratches, etc., and kept clean. Especially when using metal gaskets (oval or octagonal cross-section), the groove of the flange should match the gasket and be coated with red lead for matching to ensure good sealing.
(2) The perpendicularity between the flange surface on the piping and the centerline of the piping, as well as the error of the flange bolt holes, should be within the allowable range. Valves and piping centerlines must be aligned before installation. (3) When connecting two flanges, the first step is to evenly press the sealing surface of the flange against the gasket, ensuring that the flange is connected with equal bolt stress.
(4) When tightening bolts, use a wrench that matches the nut. When using hydraulic or pneumatic tools for tightening, be careful not to exceed the specified torque.
(5) The fastening of flanges should avoid uneven force and should be tightened in a symmetrical and intersecting direction. (6) After installing the flange, it is necessary to confirm the firmness and uniformity of all bolts and nuts.
(7) The material of bolts and nuts must comply with regulations. After tightening, it is advisable for the bolt head to protrude two pitches from the nut.
(8) To prevent loosening caused by vibration during the fastening of bolts and spirals, washers should be used. To avoid adhesion between threads at high temperatures, anti sticking agent (molybdenum disulfide) should be applied to the threaded area during installation.
(9) For valves above 200 degrees Celsius, after the temperature rises, the flange connecting bolts, valve cover fastening bolts, pressure sealing bolts, and packing pressure cover bolts must be tightened again.
(10) Low temperature valves are installed at atmospheric temperature. In practical applications, when the medium passes through, it becomes a low-temperature state. Due to the formation of temperature differences, flanges, gaskets, bolts, and nuts will shrink. Moreover, due to the different materials of these components, their coefficients of linear expansion are also different, creating an environment that is very prone to leakage. Starting from this objective situation, when tightening bolts at atmospheric temperature, it is necessary to use torque that takes into account the shrinkage factors of each component at low temperatures.
1.3.7 Installation of welded connection valves
(1) The socket of socket welding and the groove processing of butt welding should be correct and comply with relevant standards and regulations.
(2) During welding, it is necessary to prevent iron filings and welding beans from entering the piping, and tungsten inert gas shielded welding should be used.
(3) When welding, the valve should be in a slightly open state.
(4) Welding materials should be selected correctly based on the valve and piping materials. When using coated welding electrodes, it is necessary to check the storage condition of the electrodes and confirm whether a suitable drying treatment for the type of coated welding electrode has been adopted.
(5) Personnel engaged in welding operations should meet the requirements of welding technicians.
(6) When heat treatment is required after welding, the time and temperature curve records of the heat treatment should be checked.
(7) The welding area should undergo visual inspection or non-destructive testing to confirm the absence of harmful defects such as cracks, weld beads, and undercutting.
Five connection methods for valves:
1. Flange connection valve: The valve body has a flange and is connected to the pipeline using a flange.
2. Threaded connection valve: The valve body has internal or external threads and is connected to the pipeline using threads.
3. Welded connection valve: The valve body has a welded joint and is connected to the pipeline by welding.
4. Clamp connected valve: The valve body has a clamp mouth and is connected to the pipeline using clamps.
5. Card sleeve connected valve: a valve that uses a card sleeve to connect to the pipeline.
Welding and Silver Brazing.