1. Leakage of stuffing

This is the main aspect of running, running, dripping and leaking. It is often seen in factories.

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The reasons for the leakage of the packing letter are the following points:

(1) the packing is not suitable for the corrosion, temperature and pressure of the working medium; (2) the filling method is not correct, especially the whole packing is placed in the coil, which is the most easy to produce leakage; 3. The machining precision of the stem or the surface finish is not enough, or has the ellipticity, or there is a mark; (4) the valve rod has been pitting or rusty because of the lack of protection in the open air; 5 The valve stem is bent; 6. The packing has been used too long and has been aging;

The methods to eliminate the leakage of packing are: (1) correct selection of filler; (2) the correct packing; (3) the failure of the valve stem to be repaired or replaced, the lowest surface finish is to reach 5, and more importantly, more than 8 and no other defects should be reached; 4. Valve stem bending should be straightened or updated; 6. After using a certain time, the filling should be replaced; the operation should pay attention to smooth, slow open the slow off, prevent temperature change or medium impact.

2. Leakage of closed parts

Usually the leakage of stuffing box is called leakage, and the closing part is called internal leakage. The leakage of the closure is not easy to find in the valve.

The leakage of closed parts can be divided into two categories: one is the leakage of the sealing surface and the other is the leakage of the seal ring.

The causes of leakage are: (1) the sealing surface is not good grinding; (2) the sealing ring is not tight with the valve seat and valve; (3) the valve and the valve rod are not tightly connected; (4) the valve stem is bent and twisted to make the upper and lower closing parts wrong; (5) shut down too fast, the sealing surface is not good or long damaged; 6. Material selection is not suitable, the corrosion of medium can not stand; The cut-off valve and gate valve are used as the regulating valves. The sealing surface can not withstand the erosion of the high speed flow medium; some medium, gradually cooling after the valve is closed, makes the dense cover slit and also produces erosion. The impurities are embedded, or the mechanical parts fall off in the production system to block the spool so that the valve can not be tightly closed.

The preventive measures are:

Before use, we must carefully test the leakage, find the leakage of sealing surface or the leakage of the root of the seal ring, and then use it. Secondly, check the valve parts in advance, the valve rod and the valve can not be used to connect the valve with the valve stem. If the contact is not good or obstruct, it should be opened at once, let the sundries outflow and then close carefully; (4) when selecting the valve, not only the corrosion resistance of the valve body should be considered, but also the corrosion resistance of the closed parts should be considered; 5. When the valve is cooled and the temperature difference is large after the valve is closed, the valve should be closed again after the cooling; and when the valve seat, the valve and the sealing ring are threaded, the padding can be used as a filler between the thread, so that there is no gap.

3, the stem failure of the stem

The stem failure causes: (1) the excessive operation of the thread damage; (2) the lack of lubrication or lubricant failure; (3) the bending and twisting of the valve stem; (4) the lack of surface finish; (5) not enough tolerance, too tight; (6) the valve stem nut is inclined; and the material selection is improper, for example, the valve stem and the stem nut are the same material, easy to bite; The thread is corroded by the medium (the valve of the dark rod or the stem nut in the lower valve); the open-air valve is not protected, the stem thread is covered with dust, or it is rusted by the rain and frost.

Methods of prevention:

(1) careful operation, when closed, do not make the strong force, do not go to the dead point when opening, after opening enough to turn the hand wheel one or two laps, so that the thread is close to close, so as to avoid the medium push up the valve rod upward; 2. Check the lubrication condition, keep the normal lubrication state; and do not use the long lever to open and close the valve, and use the short lever. People should strictly control the force position in order to prevent the bending valve stem (the valve directly connected by the handwheel and stem); (4) improve the machining or repair quality to meet the standard requirements; (5) the material should resist corrosion, adapt to the working temperature and other working conditions; (6) the stem nut does not use the same material as the stem; and the plastic is used as the stem. Nut, to check the strength, not only consider the corrosion resistance and the friction coefficient is small, must consider the strength problem, not strength is not used; open-air valve to add valve stem protection sleeve; often open the valve, to regularly turn the handwheel, so as to avoid the stem rust.

4. Other

Gasket leakage: the main reason is corrosion resistance, not suitable for working temperature and working pressure, and the temperature change of high temperature valve. Precaution: adopt the washer suitable for working conditions, check whether the gasket material is suitable for new valve, and replace it if it is not suitable. For high temperature valves, tighten the bolts once in use.

Valve body cracking: General freezing. When it is cold, the valve should have heat preservation and heat tracing measures, otherwise the water should be discharged from the valve and the connecting pipe (such as the plug of the valve bottom, and the plug can be opened).

Handwheel damage: impact or long lever operation. As long as the operator and other concerned personnel pay attention, it can be avoided.

Packing gland fracture: the force is uneven when the packing is pressed, or the gland (usually cast iron) has defects. To tighten packing, screw the screws symmetrically. When manufacturing, not only attention should be paid to large parts and key parts, but also attention should be paid to the sub requirements such as stamping, otherwise the use will be affected.

Valve stem and valve plate connection failure: gate valve adopts the valve stem long square head and gate T shaped groove connection more form, T shaped slot is sometimes not processed, so the valve stem long head wear faster. Mainly from the manufacturing side. But the use of units can also make T groove processing, so that it has a certain degree of finish.

Double gate valve gate plate cannot press tight cover: the tension of the double gate is produced by the top wedge, some gate valves, the top wedge material is not good (low grade cast iron), and it is worn or broken in use soon. The top wedge is a small piece with little material. The unit can be made of carbon steel and replaced with the original cast iron.