Industry new

You can understand the failures and precautions of common valves.

One: packing leak

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 most likely to cause leakage;
3, the valve stem processing accuracy or surface finish is not enough, or has ovality, or has a score;
4, the valve stem has been pitting, or rust due to lack of protection in the open air;
5, the valve stem is bent;
6, the filler used for too long, has been aging;
7, the operation is too fierce.

The way to eliminate filler leakage is:
1, the correct choice of filler;
2, according to the correct loading;
3. If the valve stem is unqualified, it must be repaired or replaced, and the surface finish must be at least ▽
4, more importantly, to reach ▽8 or more, and 2, no other defects;
5, take protective measures to prevent rust, have been replaced with rust;
6, the stem bending should be straightened or updated;
7, after the filler is used for a certain period of time, it must be replaced;
8, the operation should pay attention to smooth, slow opening and slowing down, to prevent temperature drastic changes or medium impact.

Two: closure leak
The stuffing box leakage is usually called an external leak, and the closing part is called an internal leak. 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 cause of the leak:
1, the sealing surface is not well polished;
2, the sealing ring is not tightly matched with the valve seat and the valve disc;
3, the valve flap and the valve stem are not securely connected;
4, the valve stem is twisted and twisted, so that the upper and lower closing members are not centered;
5, the closing is too fast, the sealing surface is not well contacted or has been damaged;
6, the material is not properly selected, can not withstand the corrosion of the medium;
7, the shut-off valve, gate valve used as a regulating valve. The sealing surface cannot withstand the erosion of the high velocity flowing medium;
8, some media, gradually cooled after the valve is closed, so that the sealing surface appears slit, it will also produce erosion phenomenon;
9, some sealing surfaces and the valve seat, the valve flap between the threaded connection, easy to produce oxygen concentration battery, corrosion loose;
10, due to the inclusion of impurities such as welding slag, rust, dust, or mechanical parts in the production system to block the valve core, so that the valve can not be closed.

The methods to prevent leakage are:
1. Before use, you must carefully test the test leak and find that the sealing surface leaks or the root of the seal leaks, and then use it after handling it;
2, to check in advance whether the valve parts are intact, can not use the valve stem bending or valve valve and valve stem connection unreliable valve;
3, the valve should be tight to make it stable, do not make it violent, if you find that the contact between the sealing surface is not good or has a barrier, you should immediately open a little, let the logistics out, and then carefully close;
4. When selecting the valve, not only the corrosion resistance of the valve body but also the corrosion resistance of the closing member should be considered;
5, according to the structural characteristics of the valve, the correct use, the parts that need to adjust the flow should use the regulating valve;
6. For the case where the medium is cooled after the valve is closed and the temperature difference is large, the valve should be closed after cooling;
7. When the valve seat, valve disc and sealing ring are threaded, the Teflon tape can be used as the filler between the threads so that there is no gap;
8, the valve may fall into the impurity, should be added in front of the valve filter.

Three: The reasons for the failure of the valve stem are:
1, the operation is too strong to make the thread damage;
2, lack of lubrication or lubricant failure;
3, the valve stem is twisted and twisted;
4, not enough;
5, the tolerance is not allowed, the bite is too tight;
6, the stem nut is tilted;
7, the material is not properly selected, such as the stem and stem nut are the same material, easy to bite;
8, the thread is corroded by the medium (refer 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 it is rusted by rain, frost and snow.

Ways to prevent valve stem lift failure:
1, meticulous operation, do not make the violent when closing, do not go to the top dead point when opening, turn the handwheel one or two times after opening enough, so that the upper side of the thread is tightly closed, so as to prevent the medium pushing the valve stem upward impact;
2, often check the lubrication and maintain normal lubrication;
3, do not use long levers to open and close the valve, workers who are accustomed to using short levers must strictly control the force of the size to prevent the valve stem (refers to the valve directly connected to the hand wheel and valve stem);
4, improve the quality of processing or repair, to meet the requirements of the specification;
5, the material should be corrosion resistant, adapt to working temperature and other working conditions;
6, the stem nut should not use the same material as the valve stem;
7, when using plastic as the stem nut, to check the strength, not only consider the corrosion resistance and friction coefficient is small, but also must consider the strength problem, do not use if the strength is not enough;
8, the open-air valve should be added with a valve stem cover;
9, normally open the valve, you must turn the handwheel regularly to avoid the valve stem rust

Four: Other

1: Gasket leakage: The main reason is not corrosion resistance, not suitable for working temperature and working pressure; and temperature change of high temperature door.
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.
2: 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).
3: 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. :
4: Fracture of the packing gland: uneven force is applied when the packing is pressed, or the gland (generally cast iron) is defective. 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.
5: The connection between the valve stem and the valve plate is unsatisfactory: the gate valve adopts the valve block long square head and the gate T-shaped groove to connect more forms, and the T-shaped groove sometimes does not process, so the valve stem long square head 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.
6: The gate of the double gate valve can't 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.

PREVIOUS：What are the reasons for the damage to the seNEXT：What are the advantages and characteristics o