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Gate valve is the most common kind of industrial valve, widely used in petroleum, petrochemical, power station, long-distance pipeline and shipbuilding and other industrial fields.
As a fluid control equipment, gate valve opening and closing parts are gate plate, through the up and down movement of the gate plate, switch open and closed state, so as to achieve the function of cutting off or connecting the medium in the pipeline.
If the gate valve leaks, it is easy to bring hidden danger to the pipeline and equipment facilities, and may even affect the safety of life and equipment. Understanding the gate valve structure and operating principle can help us operate the gate valve correctly and better grasp the gate valve operating condition.
Once the gate valve leaks, it can be the first time to take the correct disposal method, reduce economic losses and reduce the probability of accidents. Gate valve leakage is generally divided into internal and external leakage, resulting in gate valve leakage for a number of reasons, requiring in-depth analysis and research, in order to take the appropriate disposal measures.
Wedge seal can be divided into two categories, the first hard seal, also known as the metal wedge ring; the second is a soft seal, also known as the composite graphite wedge ring. If the precision of the wedge seal ring is low, it is easy to cause internal leakage of the gate valve.
Valve production and operation in the process of unstable working conditions, its pressure and ambient temperature may occur large changes in magnitude, which makes the sealing ring to withstand the larger impact pressure, scouring force and deformation, resulting in the sealing ring and the gap between the valve body is growing, resulting in valve leakage.
Staff disassemble the valve for overhaul process, the installation of wedge-shaped sealing ring when the sealing surface is not cleaned up, leaving some fine particles and impurities, these fine impurities in the valve operation process may scratch the sealing surface, once the sealing surface to form a penetrating scratch, it will trigger the valve leakage.
In the design of wedge-shaped sealing ring need to pay more attention to the strength and corrosion resistance of the sealing ring, sealing ring surface hardness than the cover sealing layer of the hardness is smaller, but also in line with the role of external conditions can occur under the plastic deformation, the media may also corrode the wedge-shaped sealing ring during a long period of operation, thus triggering the gate valve leakage.
Gate valve switch by the actuator control, the actuator relies on liquid, gas, electricity or other energy and through the motor, cylinder or other devices will be converted into driving action, drive the valve to the full open or fully closed position. The actuator is not open or closed in place, which will lead to the gate valve can not be fully open or closed, resulting in internal leakage of the valve.
Casting valve body often appear casting defects, such as: porosity, slag, cracks, sand eyes, etc., if these defects are not found in the factory, or found without taking the correct repair measures, in the field in the use of the process will appear valve leakage.
Gate valve internal leakage or a small amount of leakage, the first job is to tighten and fix the pressure plate of the valve body, and by increasing the bolt to strengthen the pressure plate and wedge-shaped sealing ring between the preload strength, which can help the plastic deformation of the sealing ring, so as to better reduce the gap between the valve body, pressure plate and sealing ring size, to avoid leakage of the valve self-sealing phenomenon. If, when tightening and fixing the bolts, the leakage volume does not change significantly stop tightening measures immediately and take other processing measures instead.
When the valve has a small internal leakage, the sealing surface or packing can be greased through the grease injection hole to temporarily alleviate the valve internal leakage. When it is easy to overhaul and maintain, the valve can be dismantled and returned to the factory for repair.
The processing of valve self-sealing leakage requires good disassembly of the valve handwheel and valve frame, first of all, we must cooperate with good craftsmen to grasp the site conditions and adjustments, and then the valve all open, and then disassemble the bolts fixed on the valve bracket, rotate the valve frame clearly after the stem does not rise and fall changes, then start to disassemble the valve frame.
After dismantling the valve frame, the valve body should be exposed in the pressure plate part of the valve, and the gap between the pressure plate and the valve body should be sealed and welded, for the consideration of sealing the leakage position after the valve frame back to the process, the welding gap size should be between five millimetres and eight millimetres, and the welding angle and the position of the pressure plate is forty-five degree angle state, and according to the actual assembly situation for grinding.
The actuator zero position is not set accurately and the full closing position of the valve is not reached. Ensure that the actuator can accurately open or close the valve fully by manually opening and closing the valve fully and then adjusting the actuator zero position.
When there is a valve body leakage, the valve manufacturer can repair the valve body defects by welding, or return to the factory to repair and replace the valve body. First of all, the valve body defects exist to judge, there are penetrating cracks, penetrating defects, and more than a certain area of shrinkage is not allowed to repair, in this case, only to the plant to replace the valve body. For the valve body defects can be welded, to develop a suitable welding process, to determine the welding method, welding rod material, welding stress relief, and welding location for suitable non-destructive testing to ensure that the repair meets the requirements.
Gate valve leakage causes and processing measures to analyze, can be taken to improve the bolt preload, online with pressure blocking and injection of sealant processing measures to alleviate or eliminate valve leakage. With pressure blocking to be operated by professional staff with a solid foundation, through welding reinforcement blocking valve body end face, packing letter and pressure plate gap, injection of sealant and other ways to better avoid leakage accidents, thus bringing reference and guidance for solving similar valve leakage problems.
