Common faults and solutions of the most common val

2022-08-06
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Common faults and solutions of general valves

1. Stuffing box leakage: This is the main aspect of running, emitting, dripping and leakage, which is often seen in the factory

the causes of stuffing box leakage are as follows:

① the stuffing is incompatible with the corrosion, temperature and pressure of the working medium; ② The filling method is wrong, especially when the whole packing is put in by circling, it is most likely to cause leakage; ③ The machining accuracy or surface finish of the valve rod is not enough, or there is ovality or scoring; ④ The valve rod has pitted or rusted due to lack of protection in the open air; ⑤ The valve rod is bent; ⑥ The filler has been used for too long and is aging; ⑦ The operation is too fierce

the methods to eliminate packing leakage are as follows: ① correct selection of packing; ② Fill according to the correct; ③ If the processing of the valve rod is unqualified, it shall be repaired or replaced. The surface finish shall be at least ▽ 5, and more importantly, it shall be at least ▽ 8 without other defects; ④ Take protective measures to prevent corrosion, and replace the rusted ones; ⑤ The bent valve rod shall be straightened or renewed; ⑥ The filler shall be replaced after a certain period of use; ⑦ Pay attention to stable operation, slow opening and slow closing to prevent sudden temperature change or medium impact

2. Leakage of closing parts: generally, the leakage of stuffing box is called external leakage, and the leakage of closing parts is called internal leakage. The leakage of the closing part is not easy to find in the valve

the leakage of closing parts can be divided into two types: one is the leakage of sealing surface, and the other is the leakage of sealing ring root

the causes of leakage are as follows: ① the sealing surface is not well ground; ② The sealing ring is not tightly matched with the valve seat and disc; ③ The connection between valve disc and valve rod is not firm; ④ The valve rod is bent and twisted to make the upper and lower closing parts misaligned; ⑤ Closing too fast, the sealing surface is not in good contact or has been damaged; ⑥ Improper material selection, unable to withstand medium corrosion; ⑦ The stop valve and gate valve are used as regulating valves. The sealing surface cannot withstand the erosion of high-speed flowing medium; ⑧ Some media will gradually cool down after the valve is closed, resulting in fine cracks on the sealing surface and erosion; ⑨ Some sealing surfaces are connected with valve seat and disc by thread, which is easy to produce oxygen concentration difference battery and loose corrosion; ⑩ The valve cannot be closed tightly due to the embedding of welding slag, rust, dust and other impurities, or the falling off of mechanical parts in the production system blocking the valve core. The preventive measures for inlet pump valves are as follows: ① pressure and leakage test must be conducted carefully before use. If leakage is found on the sealing surface or at the root of the sealing ring, it should be handled before use; ② Check whether all parts of the valve are in good condition in advance. Do not use the valve with bent valve rod or unreliable connection between valve disc and valve rod; ③ The valve shall be firmly closed without strong force. In case of poor contact or blocking between sealing surfaces, it shall be opened immediately to allow debris to flow out, and then it shall be carefully closed; ④ When selecting valves, not only the corrosion resistance of the valve body, but also the corrosion resistance of the closing parts shall be considered; ⑤ According to the structural characteristics of the valve, it should be used correctly. The components that need to adjust the flow should use the regulating valve; ⑥ If the medium is cooled and the temperature difference is large after closing the valve, close the valve after cooling; ⑦ When the valve seat, disc and sealing ring are connected by thread, polytetrafluoroethylene tape can be used as the packing between the threads to make it free of gap; ⑧ For valves that may fall into impurities, a filter shall be added in front of the valve

3. Valve rod lifting failure:

the reasons for valve rod lifting failure include: ① thread damage caused by excessive operation; ② Lack of lubrication or lubricant failure; ③ Bending and twisting of valve rod; ④ Insufficient surface finish; ⑤ The fitting tolerance is inaccurate and the bite is too tight; ⑥ The valve rod nut is inclined; ⑦ Improper material selection, for example, the valve rod and valve rod nut are of the same material, which is easy to bite; ⑧ The thread is corroded by the medium (refers to the Non rising stem valve or the valve with the stem nut at the lower part); ⑨ The open-air valve is not protected, and the valve rod thread is covered with dust or sand, or corroded by rain, dew, frost and snow

prevention methods: ① operate carefully, do not use force when closing the asymmetric fatigue test, do not reach the top dead center when opening, turn the hand wheel back oneortwo turns after opening enough to make the upper side of the thread close, so as to avoid the upward impact of the medium pushing the valve rod; ② Regularly check the lubrication condition and maintain the normal lubrication state; ③ Do not use a long lever to open and close the valve. Workers who are used to using a short lever should strictly control the degree of force to prevent twisting the valve stem (referring to the valve directly connected with the handwheel and the valve stem); ④ Improve the processing or repair quality to meet the specification requirements; ⑤ The material shall be corrosion-resistant and adapt to the working temperature and other working conditions; ⑥ The valve rod nut shall not be made of the same material as the valve rod; ⑦ When plastic is used as the valve stem nut, the strength shall be checked, not only the good corrosion resistance and small friction coefficient, but also the strength. If the strength is not enough, do not use it; ⑧ Open air valves shall be equipped with valve stem protective sleeve; ⑨ When the valve is normally open, the hand wheel shall be rotated regularly to prevent the valve stem from rusting

4. Others: gasket leakage: the main reason is that it is not corrosion resistant and does not adapt to the working temperature and pressure; There are also temperature changes of high-temperature valves. Prevention method: adopt gaskets suitable for working conditions. For new valves, check whether the gasket material is suitable. If not, replace it. For the high temperature valve of biosynthesis method, the bolts shall be tightened again during use

valve body cracking: generally caused by freezing. In cold weather, the valve shall be provided with heat preservation and tracing measures, otherwise the water in the valve and connecting pipeline shall be drained after shutdown (if there is a valve bottom plug, the plug can be opened for drainage)

handwheel damage: it is caused by impact or long bar and strong operation around the target bar of innovation driven transformation and development in Ningbo. It can be avoided as long as the operators and other relevant personnel pay attention to it

the packing gland is broken: the force is uneven when pressing the packing, or the gland (usually cast iron) is defective. When pressing the packing, the screws shall be rotated symmetrically without deflection. During manufacturing, attention shall be paid not only to large and key parts, but also to secondary elements such as gland, otherwise the use will be affected

failure of connection between valve rod and valve plate: the gate valve adopts many forms of connection between the rectangular head of valve rod and the T-shaped groove of ram, and sometimes the T-shaped groove is not processed. Therefore, the rectangular head of valve rod with an annual output of 18000 tons is rapidly worn in the first phase. Mainly from the manufacturing aspect. However, the user can also make up the T-shaped groove to make it have a certain degree of finish

the ram of the double ram valve cannot be pressed tightly against the face: the tension of the double ram is generated by the top wedge. For some gate valves, the top wedge material is poor (low-grade cast iron), which will be worn or broken soon after use. The top wedge is a small piece with few materials. The user can make it with carbon steel and replace the original cast iron

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