The valve continuously maintains and completes the given functional requirements within a certain working time, and the performance of maintaining the given parameter value within the specified range is called failure-free. When the performance of the valve is damaged, it will be A malfunction will occur.
1. Stuffing box leakage
This is the main aspect of running, running, dripping, and leaking, and it is often seen in factories.
The reasons for the leakage of the stuffing box are as follows:
①The material is not compatible with the corrosiveness, temperature and pressure of the working medium;
②The filling method is wrong, especially when the whole packing is placed in a spiral, it is most likely to cause leakage;
③The machining accuracy or surface finish of the valve stem is not enough, or there is ovality, or there are nicks;
④The valve stem has been pitted, or rusted due to lack of protection in the open air;
⑤The valve stem is bent;
⑥The packing has been used for too long and has aged;
⑦The operation is too violent.
The method to eliminate packing leakage is:
① Correct selection of fillers;
②Fill in the correct way;
③ If the valve stem is unqualified, it should be repaired or replaced, and the surface finish should be at least ▽5, and more importantly, it should reach ▽8 or above, and there are no other defects;
④ Take protective measures to prevent rust, and those that have been rusted should be replaced;
⑤Bending of the valve stem should be straightened or updated;
⑥After the packing has been used for a certain period of time, it should be replaced;
⑦The operation should be stable, open slowly and close slowly to prevent sudden temperature changes or medium impact.
2. Leakage of closing parts
Usually, the leakage of the stuffing box is called external leakage, and the closing part is called internal leakage. Leakage of closing parts, inside the valve, is not easy to find.
The leakage of closing parts 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:
①The sealing surface is not well ground;
②The sealing ring is not tightly matched with the valve seat and valve disc;
③The connection between the valve disc and the valve stem is not firm;
④The valve stem is bent and twisted, so that the upper and lower closing parts are not centered;
⑤Close too fast, the sealing surface is not in good contact or has long been damaged;
⑥ improper material selection, can not withstand the corrosion of the medium;
⑦Use globe valve and gate valve as regulating valve. The sealing surface cannot withstand the erosion of high-speed flowing medium;
⑧Some media will gradually cool down after the valve is closed, so that the sealing surface will appear slits, and erosion will also occur;
⑨Threaded connection is used between some sealing surfaces and valve seat and valve disc, which is easy to generate oxygen concentration difference battery and corrode loose;
⑩The valve cannot be closed tightly due to the embedding of impurities such as welding slag, rust, dust, or mechanical parts in the production system that fall off and block the valve core.
The preventive measures are:
①Before use, you must carefully test the pressure and leak, and find the leakage of the sealing surface or the root of the sealing ring, and then use it after treatment;
②It is necessary to check in advance whether the various parts of the valve are in good condition. Do not use the valve that the valve stem is bent or twisted or the valve disc and the valve stem are not connected securely;
③The valve should be closed firmly, not violently. If you find that the contact between the sealing surfaces is not good or there is obstruction, you should immediately open it for a little while to let the debris flow out, and then close it carefully;
④When choosing a valve, not only the corrosion resistance of the valve body, but also the corrosion resistance of the closing parts should be considered;
⑤ In accordance with the structural characteristics of the valve and correct use, the components that need to adjust the flow should use the regulating valve;
⑥For the case where the medium is cooled and the temperature difference is large after closing the valve, the valve should be closed tightly after cooling;
⑦When the valve seat, valve disc and sealing ring are connected by thread, PTFE tape can be used as the packing between the threads, so that there is no gap;
⑧A filter should be added in front of the valve for the valve that may fall into impurities.
3. Valve stem lift failure
The reasons for the valve stem lifting failure are:
①The thread is damaged due to excessive operation;
② lack of lubrication or lubricant failure;
③The valve stem is bent and twisted;
④The surface finish is not enough;
⑤ The fit tolerance is inaccurate, and the bite is too tight;
⑥The valve stem nut is inclined;
⑦ Improper material selection, for example, the valve stem and the valve stem nut are made of the same material, which is easy to bite;
⑧The thread is corroded by the medium (referring to the valve with the dark stem valve or the valve with the stem nut at the bottom);
⑨The open-air valve lacks protection, and the valve stem thread is covered with dust and sand, or rusted by rain, dew, frost and snow.
Methods of prevention:
① Careful operation, do not force when closing, do not reach the top dead center when opening, turn the handwheel one or two turns after opening enough to make the upper side of the thread close, so as to prevent the medium from pushing the valve stem upwards to impact;
②Check the lubrication condition frequently and maintain the normal lubrication state;
③Do not open and close the valve with a long lever. Workers who are accustomed to using a short lever should strictly control the amount of force to prevent twisting the valve stem (referring to the valve directly connected with the handwheel and the valve stem);
④Improve the quality of processing or repair to meet the specification requirements;
⑤The material should be resistant to corrosion and adapt to the working temperature and other working conditions;
⑥The valve stem nut should not be made of the same material as the valve stem;
⑦ When using plastic as the valve stem nut, the strength should be checked, not only good corrosion resistance and small friction coefficient, but also the strength problem, if the strength is not enough, do not use it;
⑧The valve stem protection cover should be added to the open air valve;
⑨For normally open valve, turn the handwheel regularly to prevent the valve stem from rusting.
4. Other
Gasket leakage:
The main reason is that it is not resistant to corrosion and does not adapt to the working temperature and pressure; and the temperature change of the high temperature valve.
Use gaskets suitable for working conditions. Check whether the gasket material is suitable for new valves. If it is not suitable, it should be replaced. For high temperature valves, tighten the bolts again during use.
Cracked valve body:
Usually caused by freezing. When the weather is cold, the valve must have thermal insulation and heat tracing measures. Otherwise, the water in the valve and the connecting pipeline should be drained after production is stopped (if there is a plug at the bottom of the valve, the plug can be opened to drain).
Damaged handwheel:
Caused by impact or strong operation of long lever. It can be avoided as long as the operator and other concerned personnel pay attention.
The packing gland is broken:
Uneven force when compressing packing, or defective gland (usually cast iron). Compress the packing, rotate the screw symmetrically, and do not skew. When manufacturing, not only should pay attention to large and key parts, but also pay attention to secondary parts such as glands, otherwise it will affect the use.
The connection between the valve stem and the valve plate fails:
The gate valve adopts many forms of connection between the rectangular head of the valve stem and the T-shaped groove of the gate, and the T-shaped groove is sometimes not processed, so the rectangular head of the valve stem wears quickly. Mainly from the manufacturing aspect to solve. However, the user can also make up the T-shaped groove to make it have a certain smoothness.
The gate of the double gate valve cannot press the cover tightly:
The tension of the double gate is generated by the top wedge. For some gate valves, the top wedge is of poor material (low-grade cast iron), and will be worn or broken soon after use. The top wedge is a small piece, and the material used is not much. The user can make it with carbon steel and replace the original cast iron.
Post time: Apr-18-2022
