Causes of Valve Leakage and Introduction of Preventive Measures

The main causes of valve leakage are running, leaking, dripping and leakage, which are often seen in factories. Four common reasons are as follows:
1. Leakage of packing box
(1) The corrosiveness, temperature and pressure of filler and working medium are not suitable; (2) incorrect filling method, especially when the whole filler is placed in a circle, is most likely to cause leakage; (3) insufficient processing accuracy or surface finish of the valve stem, or ellipticity or marks; (4) the valve stem has been pitted or rusted due to lack of protection in the open air; Stem bending; _Packing used too long, has been aging; _Operation is too fierce.
The methods of eliminating packing leakage are as follows: (1) correct selection of fillers; (2) correct filling; (3) unqualified stem processing should be repaired or replaced, and the surface finish should be as low as_5, more importantly, more than_8 without other defects; (4) protective measures should be taken to prevent rust and replace the rusted stem. Stem bending should be straightened or renewed; Packing should be replaced after a certain period of time; _Operation should be smooth, slow opening and slow closing, to prevent temperature drastic change or medium impact.
2. Leakage of Closed Parts
Usually the leakage of packing box is called leakage, and the closure is called internal leakage. Leakage of the closure is not easy to find in the valve.
Leakage of closure can be divided into two categories: one is leakage of sealing surface, the other is leakage of sealing ring root.
The causes of leakage are: (1) poor grinding of sealing surface; (2) loose matching of sealing ring with seat and disc; (3) weak connection between disc and stem; (4) unstable bending and twisting of valve stem, which makes the upper and lower closures misaligned; (5) too fast closure, poor contact or long-term damage of sealing surface; (5) improper selection of materials, which can not withstand the corrosion of medium. _Use globe valves and gate valves as control valves. Sealing surface can not withstand the erosion of high-speed flowing media; _Some media gradually cool down after the valve closes, resulting in seams and erosion phenomenon; _Thread connection between some sealing surface and valve seat, valve disc is easy to produce oxygen concentration battery, corrosion loosening; _Because of welding slag, rust, dust and so on. Impurity embedded, or mechanical parts in the production system fall off and block the valve core, so that the valve can not be closed.
The precautions are as follows:
Before using, it is necessary to test the leakage carefully, find the leakage of sealing surface or the leakage of sealing ring root, and then use it after handling it well. Second, check the integrity of all parts of the valve beforehand, and can not use the valve stem bending and twisting or unreliable connection between the valve disc and the stem. Third, the valve should be closed firmly and not vigorously, such as finding the sealing surface. If the contact is not good or obstructive, it should be opened a little immediately to let the miscellaneous flow out, and then close carefully; (4) When choosing the valve, not only the corrosion resistance of the valve body, but also the corrosion resistance of the closing parts should be considered; (5) According to the structural characteristics of the valve, proper use should be made, and the parts that need to regulate the flow rate should be adjusted. Valve; _For the case of medium cooling and large temperature difference after closing the valve, the valve should be closed after cooling; _When the seat, disc and seal ring are connected by threads, PTFE belt can be used as filler between threads, so that there is no void; _Valves that may fall into impurities should be added with filters before the valve.
3. Stem lift failure
The reasons for the failure of valve stem lifting are as follows:
(1) Thread damage caused by excessive operation; (2) lack of lubricant or lubricant failure; (3) stem bending and torsion; (4) insufficient surface finish; (5) inaccurate tolerance, too tight bite; (5) inclined stem nut; (5) improper material selection, such as valve stem and stem nut are the same material, easy to bite; (5) thread is corroded by media (referring to hidden stem). Valves or stem nuts in the lower part of the valve; _Open-air valves lack protection, valve stem threads are covered with dust, or are corroded by rain, dew, frost and snow.
Methods of prevention:
(1) Careful operation, do not force when closing, do not reach the upper dead point when opening, turn the handwheel backward one or two times after opening enough, so that the upper side of the thread is closed, so as to avoid the medium pushing the stem upward impact; (2) check lubrication regularly to maintain normal lubrication state; and (3) do not open and close the valve with long lever, accustomed to the use of short lever workers. Man should strictly control the force distribution in order to prevent the torsion and bending of the valve stem (referring to the valve directly connected with the handwheel and stem); 4) improve the quality of processing or repair to meet the requirements of specifications; (5) materials should be corrosion-resistant to adapt to working temperature and other working conditions; (5) stem nuts should not be made of the same material as the valve stem; (5) plastic is used as the valve stem. When checking the strength of nuts, we should not only consider good corrosion resistance and low friction coefficient, but also consider the strength problem. If the strength is insufficient, we should not use them. _Open-air valves should be added with stem protection sleeve. _Open valves regularly, we should rotate the handwheel regularly to prevent the stem from rusting.
4. Other
Gasket leakage: The main reason is not corrosion-resistant, not suitable for working temperature and pressure; and high temperature valve temperature changes. Preventive method: Use gaskets suitable for working conditions. Check whether gaskets are suitable for new valves. If not, replace them. For high temperature valves, the bolt should be tightened again in use.
Body cracking: caused by general freezing. When it's cold, the valve should have insulation and heat tracing measures, otherwise after shutdown, the water in the valve and connecting pipeline should be drained clean (if there is a bottom silk plug of the valve, the silk plug can be opened to drain).
Handwheel damage: caused by impact or heavy operation of long lever. As long as operators and other relevant personnel pay attention to it, it can be avoided.
Fracture of packing gland: When pressing packing, the force is not uniform, or the gland (usually cast iron) is defective. To tighten the packing, the screw should be rotated symmetrically and not skewed. Not only in manufacturing