Views: 84 Author: Site Editor Publish Time: 2019-11-21 Origin: Site
At present, valves are widely used in various fields. If the valve is out of order, it most likely causes safety problems. So we all need to know some main fault causes of valve and preventive measures. Let's talk about it in detail below.
In the process of opening and closing the valve, sometimes it feels stuck and inflexible. Sometimes it can't be opened and closed with normal opening and closing forces. Even after opening and closing for a certain distance, it can't continue to open and close.
There are some reasons for the fault. First, the valve stem and other components are stuck, such as the packing gland tilting and hitting the valve stem. Second, the packing is not installed correctly or pressed too tightly. Third, the valve stem and other components are seized or not lubricated where the lubricant should be added. In order to prevent this kind of fault, first of all, avoid paper jam. Then loosen and install the packing correctly, and apply proper lubricant at the proper place.
Sometimes the sealing surface is bitten, the stem bite of the stem is scratched, and the threaded part of the stem is bitten. To explain the causes of these faults, we should understand the cause of scratches firstly.
First, the adhesive wear produces abrasive particles. The hardness and strength of the abrasive particles are higher than that of the base metal, and they are pressed into the soft surface to scratch the hard surface. At the same time, the hard abrasive particles are pushed and moved by the hard surface crest in the soft surface, thus ploughing the soft surface. After the friction surface is separated, the abrasive particles may be discharged, but they may still exist on the soft surface.
In the second friction, the hard surface will be scratched and a deeper and longer deep groove will be ploughed on the soft surface until the soft surface in front of the hard particles can not resist the moving force of the hard particles and is sheared, and a strip groove will be formed on the soft surface, and a scratch mark will be formed on the hard surface. If the load is severe and the contact points are few, the shear strength increases and the wear debris also increases. If it is not discharged in time, it will be pressed into the surface to form a nodule. After the nodule, the shear strength of the contact point increases and the wear debris also increases, and finally the friction tumor is formed.
The process from small nodule to friction tumor is gradually increasing. When the original moving force can not cut the friction tumor, bite and scratch damage will also occur. So bite scratch damage is a form of wear to some extent.
Secondly, the valve stem may collide with the packing sleeve and packing pad. Another is that if the medium contains boron, it will crystallize into hard particles after it is discharged, which will damage the surface of the valve rod. And as well as the part that should be lubricated without lubricant, etc.
Bite and scratch damage is some grooves caused by hard particles entering or wear of its own abrasive particles. Therefore, it is necessary to reduce the abrasive particles as much as possible to make them into powder particles, and remove the particles from the friction surface timely and fully. This requires that the friction pairs have a high degree of smoothness and good coincidence, so that the number of contact points and the contact area increases. The shear strength decreases under the same shear force, and the wear debris under shear also decreases. 。
Therefore, under the condition of constant load, it is necessary to increase the friction area or improve the finish, and to lubricate as much as possible, so as to further reduce the friction force and facilitate the removal of abrasive particles. At the same time, a chip removal groove should be opened on the wider friction surface, so that the abrasive particles can be drained into the groove and can be discharged along with the lubricating oil from the friction surface.
In order to keep the sealing surface from scratch, it is necessary to make the sealing surface work under the condition of self grinding so as to reduce the wear of abrasive particles and make the surface further refined. As a result the service life of the sealing surface will be maintained and extended.
(1) strictly control the cleanliness of valve chamber.
(2) properly improve the finish of sealing surface.
(3) increase the contact surface.
(4) improve the fitness.
(5) no hard particles enter the friction surface.
(6) the abrasive particles are eliminated rapidly and completely.
(7) hardness difference between both parties.
(8) lubricate, reduce friction and avoid direct metal contact.
(9) less than the pressure.
(10) open a chip bag or chip breaker on a soft surface.
(11) materials with large plastic flow pressure δy.
(12) materials that are not prone to cold work hardening.
Next, wipe the stem and other components. Third, install or press the package correctly to prevent medium leakage. Finally, the corresponding lubricant should be added to the lubricated part.