Common faults and preventive measures for Fengquan·General valves Common failures and precautions of general valves 1. Leakage of the stuffing box This is the main aspect of running, running, dripping and leaking, which is often seen in factories.
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The reasons for the stuffing box leakage are as follows:
1 The filler is not compatible with the corrosiveness, temperature and pressure of the working medium; 2 the filling method is wrong, especially when the whole packing is hovered, the Zui is easy to produce leakage; 3 the valve stem has insufficient processing precision or surface finish, or has ovality, Or nicks; 4 stem has been pitting, or rust due to lack of protection in the open air; 5 stem bending; 6 filler used for too long, has been aging; 7 operation is too fierce.
The method for eliminating the leakage of the packing is: 1 correct packing is selected; 2 is loaded correctly; 3 if the valve stem is unqualified, it needs to be repaired or replaced, and the surface finish is low to reach â–½5, more importantly, to reach â–½8 or above. 4, and no other defects; 4 take protective measures to prevent corrosion, has been replaced with rust; 5 stem bending should be straightened or updated; 6 filler after a certain period of time, to be replaced; 7 operation should pay attention to smooth, slow opening and closing To prevent temperature drastic changes or media impact.
2, closure parts leakage Usually the stuffing box leakage is called leakage, the closing piece is called internal leakage. The closing piece leaks inside the valve and is not easy to find.
Closed parts leaks 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 causes of leakage are: 1 the sealing surface is not well grounded; 2 the sealing ring is not tightly fitted with the valve seat and the valve disc; 3 the valve disc is not firmly connected with the valve stem; 4 the valve stem is twisted and twisted, so that the upper and lower closing members are not centered. ; 5 close too fast, the sealing surface is not well contacted or damaged early; 6 material selection is improper, can not withstand the corrosion of the medium; 7 use the shut-off valve, gate valve as a regulating valve. The sealing surface can not withstand the erosion of high-speed flowing medium; 8 some media, after the valve is closed, gradually cool, so that the sealing surface appears slit, it will also produce erosion; 9 some sealing surface and valve seat, valve Thread connection is easy to produce oxygen concentration battery, corrosion is loose; 10 due to impurities such as welding slag, rust, dust, etc., or mechanical parts in the production system fall off and block the valve core, so that the valve can not be closed.
The preventive measures are:
1Before using, you must carefully test the leak and find that the sealing surface leaks or the root of the sealing ring leaks. It should be used after being processed. 2 Check that the valve parts are in good condition, you can not use the valve stem to bend or the valve flap to connect with the valve stem. 3 valves should be closed; 3 valves should be tight to ensure stability, do not make violent, if you find that the contact between the sealing surfaces is not good or has obstacles, you should immediately open a little, let the impurities flow out, and then carefully close; 4 when using the valve Not only the corrosion resistance of the valve body should be considered, but also the corrosion resistance of the closing member should be considered. 5 According to the structural characteristics of the valve, the correct use should be made. The parts that need to adjust the flow rate should adopt the regulating valve; 6 the medium is cooled after the valve is closed. In the case of large temperature difference, the valve should be closed after cooling; when the valve seat, valve disc and sealing ring are screwed, the Teflon tape can be used as the filler between the threads to make it have no gap; Valves that may fall into the impurity should be fitted with a filter in front of the valve.
3. Valve stem lifting failure The reasons for the valve stem lifting failure are:
1 operation is too strong to make thread damage; 2 lack of lubrication or lubricant failure; 3 stem bending; 4 surface finish is not enough; 5 mismatched tolerance, bite too tight; 6 stem nut tilt; 7 material selection is not appropriate, for example The valve stem and the stem nut are of the same material and are easy to bite; the 8 thread is corroded by the medium (referring to the dark rod valve or the valve stem nut at the lower part of the valve); 9 the open air valve lacks protection, the stem thread is covered with dust sand, or The rain, frost and snow are rusted.
Prevention method:
1 Careful operation, do not make it strong when closing, do not go to the top dead point when opening, turn the handwheel one or two times after opening enough, make the upper side of the thread close, so as to avoid the medium pushing the valve stem upward impact; 2 often check the lubrication situation, Maintain normal lubrication; 3 Do not use long lever to open and close the valve. Workers who are accustomed to using short levers should strictly control the force to prevent the valve stem from being twisted (refer to the valve directly connected to the hand wheel and the valve stem); Repair quality, meet specifications; 5 materials should be corrosion resistant, adapt to working temperature and other working conditions; 6 stem nut should not use the same material as the valve stem; 7 when using plastic as the stem nut, to check the strength, can not only consider Good corrosion resistance and low friction coefficient. Also consider the strength problem. Do not use if the strength is not enough. 8 Open the valve to add the valve stem cover; 9 Normally open the valve, turn the hand wheel regularly to avoid the valve stem rust.
4. Other gasket leakage: The main reason is not corrosion resistance, not suitable for working temperature and working pressure; and temperature change of high temperature valve. Precautions: Use gaskets that are compatible with the working conditions. Check the gasket material for new valves. If it is not suitable, replace it. For high temperature valves, tighten the bolts again during use.
Valve body cracking: caused by general freezing. When the weather is cold, the valve should have heat preservation and heat tracing measures. Otherwise, the water in the valve and the connecting pipe should be drained after the production is stopped (if there is a plug at the bottom of the valve, the wire plug can be opened).
Handwheel damage: caused by impact or long lever violent operation. As long as the operator and other relevant personnel pay attention, it can be avoided.
Fracture of the packing gland: uneven force when compacting the packing, or defective gland (usually cast iron). To compress the packing, rotate the screws symmetrically without being biased. When manufacturing, not only should pay attention to large and key parts, but also pay attention to secondary parts such as gland, otherwise it will affect the use.
The connection between the valve stem and the valve plate is unsatisfactory: the gate valve adopts a large number of square stems connected to the T-shaped groove of the gate, and the T-shaped groove sometimes does not process, so that the long square head of the valve stem wears faster. Mainly from the manufacturing side to solve. However, the unit can also be used to fill the T-shaped groove to give it a certain degree of finish.
The gate of the double gate valve cannot be pressed tightly. The tension of the double gate is generated by the top wedge. Some gate valves have poor top wedge material (low grade cast iron), which will wear or break soon after use. The top wedge is a small piece. The material used is not much. The unit can be made of carbon steel and replaced with the original cast iron.
