1. Leakage of stuffing box This is the primary aspect of running, running, dripping and leaking, which is often seen in the factory. There are several reasons why stuffing box leaks occur:
(1) The corrosiveness, temperature and pressure of the filler and the working medium are not suitable; (2) The filling method is incorrect, especially the whole filler is twisted and put in, which is most likely to leak; (3) The machining accuracy or surface finish of the stem is not good, or there is ovality, or there are nicks; (4) The valve stem has been pitted or rusted due to lack of protection in the open air; (5) Stem bending; (6) The filler has been used for too long and is now aged; (7) The operation is too violent.
The way to eliminate the leakage of filler is: (1) correct selection of filler; (2) Fill according to the correct one; (3) If the valve stem processing is unqualified, it should be repaired or replaced, and the surface finish should reach at least 5, and more importantly, it should reach more than ▽8, and there are no other shortcomings; (4) Take protective measures to prevent corrosion, and replace those that have been corroded; (5) The stem bending should be straightened or updated; (6) After the filler is used, it should be replaced; (7) The operation should be smooth, slow opening and closing, to prevent drastic temperature changes or medium impact.
2. Leakage of the closing part Usually the leakage of the stuffing box is called leakage, and the leakage of the closed part is called internal leakage. The shut-off leaks, inside the valve, and is not easy to find. The leakage of the closing part can be divided into two categories: one is the leakage of the sealing surface, and the other is the leakage of the root of the sealing ring. The reasons for leakage are: (1) the sealing surface is not well ground; (2) The sealing ring is not tightly cooperated with the valve seat and valve disc; (3) The connection between the disc and the stem is not firm*; (4) The valve stem is bent and twisted, so that the upper and lower closing parts are not aligned; (5) The closing is too fast, and the sealing surface is not good to touch or has long been damaged; (6) Improper selection of data, unable to taste the corrosion of the medium; (7) Use globe valves and gate valves as regulating valves. The sealing surface cannot withstand the erosion of high-speed flowing media; (8) Some media are gradually cooled after the valve is closed, so that there are fine seams on the sealing surface, and erosion will also occur; (9) Threaded connection is selected between some sealing surfaces and valve seats and valve discs, and the oxygen concentration difference battery simply occurs, and the corrosion is loose; (10) Due to the embedding of impurities such as welding slag, rust, dust, etc., or the falling of mechanical parts in the production system, the valve can not be closed.
The precautionary measures are: (1) Before use, it is necessary to carefully test the pressure and leakage, and find that the sealing surface leaks or the root of the sealing ring leaks, and it is necessary to deal with it before use; (2) Check whether the valve parts are in good condition in advance, and do not use the valve stem bending and twisting or the valve disc and the valve stem connection is not good*; (3) The valve should be closed tightly to make it steady, not to make it violent, if it is found that the touch between the sealing surfaces is not good or there is an obstruction, it should be opened immediately to let the debris flow out, and then close it carefully; (4) When selecting valves, not only the corrosion resistance of the valve body should be considered, but also the corrosion resistance of the closing parts should be considered; (5) In accordance with the structural characteristics of the valve, the correct use, the parts that need to adjust the flow should be selected as the control valve; (6) Regarding the situation that the medium is cooled and the temperature difference is large after closing the valve, the valve should be closed tightly after cooling; (7) When the valve seat, disc and sealing ring are connected by threads, PTFE tape can be used as the packing between the threads, so that there is no open space; (8) If there is a possibility of impurities falling into the valve, a filter should be added in front of the valve.
3. Stem lifting failure The reasons for the failure of valve stem lifting are: (1) Thread damage due to excessive operation; (2) Lack of smoothness or failure of smoothing agent; (3) Stem bending and torsion; (4) The surface finish is not good; (5) The cooperation tolerance is forbidden and the bite is too tight; (6) The stem nut is tilted; (7) Improper selection of information, such as the valve stem and the stem nut are the same raw material, and they are simply bitten; (8) The thread is corroded by the medium (refers to the valve with the dark rod valve or the stem nut in the lower part); (9) The open-air valve lacks protection, and the stem thread is covered with dust and sand, which may be corroded by rain, dew, frost and snow.
Precautionary methods: (1) Operate carefully, do not make a violent effort when closing, do not reach the upper dead center when open, and turn the handwheel one or two times after opening enough, so that the upper side of the thread is sealed to prevent the medium from pushing the valve stem from impacting upward; (2) Always check the smooth condition and adhere to the normal smooth state; (3) Do not use a long lever to open and close the valve, and workers who are accustomed to using a short lever should strictly control the force scale to prevent twisting and bending the valve stem (referring to the valve where the handwheel and the valve stem are directly connected); (4) Improve the quality of processing or repair to meet the standard requirements; (5) The data should be corrosion-resistant, adapt to the working temperature and other working conditions; (6) Do not use the same raw material as the stem nut; (7) When choosing plastic as the stem nut, the strength should be checked, not only the good corrosion resistance and small friction coefficient should be considered, but also the strength must be considered. (8) The open-air valve should be equipped with a stem protection sleeve; (9) For normally open valves, the handwheel should be rotated regularly to prevent the stem from rusting.
4. Other gasket leakage: the primary reason is that it is not corrosion-resistant, and it is not suitable for working temperature and working pressure; There is also the temperature variation of the high-temperature valve.
Precautionary measures: choose gaskets that are suitable for working conditions, check whether the gasket raw materials are suitable for new valves, and replace them if they are not suitable. For high-temperature valves, tighten the bolts again when applying. Cracking of the valve body: Generally formed by freezing. When the weather is cold, the valve should have a thermal insulation and heating method, otherwise the water in the valve and the connecting pipeline should be drained clean after the shutdown (if there is a plug at the bottom of the valve, the plug can be opened for drainage). Handwheel damage: caused by striking or vigorous operation with a long lever. It can be prevented as long as operators and other relevant personnel pay attention. Packing gland breakage: uneven force when pressing the filler, or the gland (usually cast iron) has a defect. Press the packing tightly, rotate the screws symmetrically, not crookedly. When making, not only pay attention to large and key parts, but also pay attention to secondary parts such as glands, otherwise it will affect the use. Failure of the connection between the stem and the valve plate: there are many ways for the gate valve to connect the rectangular head of the stem with the T-groove of the gate, and sometimes the T-groove is not processed, so the rectangular head of the stem wears out quickly. First of all, it is dealt with from the production aspect. However, the T-groove can also be reprocessed by the application unit to give it a certain finish. The ram of the double gate valve can not be pressed tightly cover: the tension of the double ram is the top wedge occurs, and some gate valves, the top wedge raw material is not good (low grade cast iron), and it will wear or break soon after use. The top wedge is a small piece, not much information is used, and the use unit can be made of carbon steel by itself, replacing the original iron casting.
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