Analysis of causes of gate valve leakage and treatment measures
Gate valve is the most common industrial valve and is widely used in industrial fields such as petroleum, petrochemicals, power stations, long-distance pipelines and shipbuilding. As a kind of fluid control equipment, the opening and closing part of the gate valve is a gate plate. Through the up and down movement of the gate plate, the open and closed states are switched, thereby realizing the function of cutting off or connecting the medium in the pipeline. If the gate valve leaks, it can easily cause hidden dangers to pipelines, equipment and facilities, and even affect the safety of personnel and equipment.
Understanding the structure and operating principle of the gate valve can help us operate the gate valve correctly and better understand the operating status of the gate valve. Once a gate valve leaks, the correct disposal method can be taken immediately to reduce economic losses and reduce the probability of accidents. Gate valve leakage is generally divided into internal leakage and external leakage. There are many reasons for gate valve leakage, which require in-depth analysis and research before corresponding disposal measures can be taken.
① The low processing accuracy of the wedge seal ring causes internal leakage of the valve
Wedge seals can be divided into two categories. The first is a hard seal, also called a metal wedge ring; the second is a soft seal, also called a composite graphite wedge ring. If the accuracy of the wedge seal ring is low, it will easily cause internal leakage of the gate valve.
② Unstable production operation conditions lead to internal leakage of the gate valve
The working conditions during valve production and operation are unstable, and the pressure and ambient temperature may change greatly. This causes the sealing ring to withstand greater impact pressure, scouring force and deformation, causing the gap between the sealing ring and the valve body to become wider. becomes larger, causing internal leakage of the valve.
③ Insufficient valve maintenance quality causes internal leakage of the gate valve
During the process of disassembling the valve for maintenance, the staff did not clean the sealing surface when installing the wedge seal ring, leaving some small particles and impurities. These small impurities may scratch the sealing surface during the operation of the valve. Once the valve is damaged, the sealing surface will be damaged. Penetrating scratches on the sealing surface will cause valve leakage.
④ The medium corrodes the wedge seal ring causing internal leakage of the gate valve
When designing a wedge-shaped sealing ring, more attention must be paid to the strength and corrosion resistance of the sealing ring. The surface hardness of the sealing ring is smaller than the hardness of the valve cover sealing layer, and it must also be able to plastically deform under the action of external force conditions. During long-term operation, the medium may also corrode the tapered sealing ring, causing gate valve leakage.
⑤ The gate valve actuator switch is not in place, causing internal leakage of the gate valve
The gate valve switch is controlled by an actuator, which relies on liquid, gas, electricity or other energy and converts it into a driving action through a motor, cylinder or other device, driving the valve to the fully open or fully closed position. If the actuator does not open or close properly, the gate valve will not be able to fully open or close, causing internal leakage of the valve.
⑥ Defects in the valve body causing valve leakage
Casting valve bodies often have casting defects, such as pores, slag inclusions, cracks, blisters, etc. If these defects are not discovered in the factory, or if they are discovered and correct repair measures are not taken, valve defects will appear during on-site use leak.
① Fix the valve body pressure plate and increase the bolt pretightening force
When there is leakage or a small amount of leakage inside the gate valve, the first thing to do is to tighten and fix the pressure plate of the valve body, and to strengthen the pre-tightening force between the pressure plate and the wedge-shaped sealing ring by raising the bolts, which can help the sealing ring. Plastic deformation, thereby better reducing the gap size between the valve body, pressure plate and sealing ring, and avoiding leakage from the valve’s self-sealing. If the leakage volume does not change significantly when tightening and fixing the bolts, stop tightening measures immediately and take other treatment measures.
② Inject sealant through the grease injection hole
When a slight internal leakage occurs in the valve, the sealing surface or packing can be injected with grease through the grease hole to temporarily alleviate the internal leakage of the valve. When it is convenient for inspection and maintenance, the valve can be disassembled and returned to the factory for repair.
③ Weld and strengthen the gap between the valve body end face, stuffing box and pressure plate
To deal with self-sealing leakage of valves, it is necessary to disassemble the valve handwheel and valve frame. First, it is necessary to cooperate with the craftsmen to grasp and adjust the working conditions on site. Then, after all the valves are opened, the fixed parts on the valve frame are removed.
After tightening the bolts and rotating the valve frame to make sure that the valve stem does not rise or fall, start disassembling the valve frame. After the valve frame is disassembled, the valve body must be exposed at the pressure plate of the valve, and the gap between the pressure plate and the valve body must be sealed and welded. In order to consider the reassembly process of the valve frame after sealing the leakage location, welding The size of the gap should be between five millimeters and eight millimeters, and the position of the welding fillet and pressure plate should be at a 45-degree angle, and should be polished according to the actual assembly situation.
④ Check the zero position of the actuator
The zero position setting of the actuator is inaccurate and the fully closed position of the valve is not reached. By manually fully opening and fully closing the valve, and then adjusting the zero position of the actuator, ensure that the actuator can accurately fully open or fully close the valve.
⑤ Valve body repair welding or return to factory for repair
When valve body leakage occurs, the valve manufacturer can repair the valve body defects by welding, or return the valve body to the factory for repair and replacement. First of all, the defects in the valve body must be judged. Penetrating cracks, penetrating defects, and shrinkage exceeding a certain area are not allowed to be repaired. In this case, the valve body can only be returned to the factory for replacement. For valve body defects that can be repaired by welding, it is necessary to formulate appropriate welding processes, determine the welding method, electrode material, post-weld stress relief method, and conduct appropriate non-destructive testing of the welding position to ensure that the repair meets the requirements.