Common failure for industrial valves and preventive measures-Belo Valve

The industrial 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 industrial valve is destroyed, failures will occur. 

industrial valves includes like butterfly valves( center line wafer butterfly valve, manual butterfly valve, lever driving butterfly valve, butterfly valve with worm gear box, lug type butterfly valve, soft seal butterfly valves, hard seal butterfly valves, flange butterfly valves, ductile cast iron butterfly valves, stainless steel butterfly valve), gate valves(including DINF4 gate valves, DINF5 gate valves, DIN3352 gate valves, rising stem gate valves, non rising stem gate valves, soft seal gate valves, hard seal gate valves, hydraulic gate valves, sluice valves), globe valves( DIN globe valves, bellows globe valves, electric globe valve), ball valves( welded ball valves, soft seal ball valves, stainless steel ball valves, WCB ball valves, ductile cast iron ball valves, API ball valves), check valves( wafer type check valves, swing check valves, rubber disc check valves, ball type check valve, foot valve/bottom valve), fire protection valves( grooved butterfly valves, grooved gate valves, grooved strainers, grooved check valves), hydraulic control valves,etc.

Today we are gonna talk about those common failures occurred on industrial valves and what the preventive measures for those failures: 

1. the packing box of industrial valve leaks; 

The reason for leakage of industrial valve stuffing boxes are as follows: 

①the packing material is not compatible with the corrosiveness,temperature and pressure of the working medium; 

② the method to fill the packing is wrong, especially when the whole packing is placed in a spiral, it is most likely to cause leakage. 

③ the machining accuracy or surface finish of the valve stem is not enough, or there is ovality, or there are nicks; 

④ the valve stem has been pitted, or rusted due to lack of protection in the open air; 

⑤ valve stem is bent; 

⑥ the packing has been used for too long and has aged; 

⑦ operating too violently; 

The way to eliminate industrial valve packing leakage is: 

① select the right packing; 

② fill the packing in a proper way; 

③ if the valve stem is unqualified, it should be repaired or replaced, and the surface finish should at least ▽5, and for important ones, it should reach ▽8 or above, and there are no other defects; 

④ take protective measure to prevent rust, and replace the rusted ones; 

⑤ if the valve stem is bent, it should be straightened, or be replaced; 

⑥ replace the packing after it has been used for a certain period of time; 

⑦ operate smoothly, slow opening and closing to prevent sudden temperature changes or medium impact. 

2. the closing part of industrial valve leaks: 

Generally, the leakage of industrial valve stuffing box is called external leakage, and the leakage of the closing part in industrial valve is called internal leakage. The leakage of the closing part is inside the valve, which is not easy to find; 

The leakage of the closing part in industrial valve can be divided into two types: one is the leakage of the sealing surface, and the other is the leakage of the root of the sealing ring; 

The reasons for the closing part leakage in industrial valves are as follows: 

① poorly ground sealing surface; 

② the sealing ring is not tightly matched with the valve seat and valve disc; 

③ the valve disc and valve stem are not firmly connected; 

④ the valve stem is bent and twisted, causing the upper and lower closing parts to be misaligned; 

⑤ closing too fast, the sealing surface has poor contact or has long been damaged; 

⑥ improper selection of materials, which can not withstand the corrosion of the medium; 

⑦ using the globe valve and gate valve as the regulating valve. The sealing surface can not withstand the erosion of the high speed flowing medium; 

⑧ some mediums will gradually cool down after the valve is closed, so that the sealing surface will appear slits, and erosion will also occur; 

⑨ threaded connection is used between some sealing surface and valve seat and valve disc, which is easy to generate oxygen concentration cells , and corrode loose; 

⑩ due to the embedded impurities such as welding slag,rust, dust, or mechanical parts in the production system that fall off and block the valve core, the valve cannot be closed tightly; 

The prevention methods for leakage of closing part in industrial valves are as follows: 

① before use, it is necessary to carefully do the pressure test and leakage test, once find there is a leakage on the sealing surface or on the root of the sealing ring, use it after repair; 

② it is necessary to check in advance whether all parts of the valve are in good condition. Do not use a valve with a twisted valve stem or a valve with a loose connection between the valve disc and the valve stem; 

③ the valve should be closed firmly not violently. If it is found that the contact between the sealing surface is not good or there is obstruction, it should be opened a little immediately to let the debris flow out, and then closed carefully. 

④ when selecting a valve, we not only should consider the corrosion resistance of the valve body, but also should consider the corrosion resistance of the closing part; 

⑤ all valves should be used correctly according to the structural characteristics of those valves, the components that need to adjust the flow should use the regulating valve; 

⑥ for the case where the medium is cooled and the temperature difference is large after the valve is closed, the valve should be closed tightly after cooling; 

⑦ when the valve seat, valve disc and sealing ring are connected by thread, PTFE material can be used as the packing between the threads, so there is no gap; 

⑧ for valves that may fall into impurities, a filter or strainer should be added before the valve; 

3. the valve stem of industrial valve lifting failure;

The reasons for the valve stem lifting failure are as follows: 

① violent operation will damage the thread; 

② lack of lubrication or lubricant failure; 

③ valve stem is bent; 

④ insufficient surface finish; 

⑤ inaccurate fit tolerance, bit too tight; 

⑥ stem nut tilts; 

⑦ improper material selection, such as the valve stem and the valve stem nut are the same material, which is easy to bite; 

⑧ the thread is corroded by the medium(referring to the non rising stem valve or the valve with stem nut at the bottom); 

⑨ the valve in the open air lacks protection, and the valve stem thread is covered with dust and sand, or rusted by rain, dew frost and snow; 

Methods for prevention: 

① careful operation, do not force when closing, do not reach the top dead point, when opening,turn the hand wheel one or two turns back to make the upper side of the thread close, so as to prevent the medium from pushing the valve stem upwards to impact; 

② check the lubrication condition frequently and maintain normal lubrication condition; 

③ do not use long levers to open and close the valve. Workers who are accustomed to using short levers should strictly control the force to prevent twisting the valve stem(referring to the valve where the hand wheel is connected with valve stem directly); 

④improve processing or repair quality to meet specification requirements; 

⑤ the material selected should be corrosion-resistant, suitable for working temperature and other working conditions; 

⑥ do not use the valve stem nut of the same material as the valve stem; 

⑦ when using plastic as valve stem nut, it is necessary to check the strength,not only to consider good corrosion resistance and small friction coefficient, but also to consider the strength problem, if the strength is not enough, do not use it; 

⑧ valve in open air should add the valve stem protection cover. 

⑨ turn the hand wheel regularly to prevent the valve stem from rusting; 

4. Other failures of the industrial valve:

The gasket of industrial valve leaks: 

Reason: The main reason for gasket leakage is that the gasket of the industrial valve is not resistant to corrosion and does not adapt to the working temperature and pressure; and the temperature change of the high temperature valve; 

Method for prevention: use a gasket suitable for the working conditions, check whether the gasket material is suitable for the new valve. If it is not suitable, it should be replaced. For the high temperature valves, tighten the bolts again during use; 

Industrial valve body cracks: 

Usually the crack is caused by freezing. When the whether 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 the water). 

The hand wheel in the industrial valve damages: 

The damage of hand wheel is generally caused by impact or forceful operation of long lever. It can be avoided as long as the operator and other concerned personnel pay attention; 

The packing gland of industrial valve is broken: 

Uneven force is used when compressing the packing, or gland is defective(usually is cast iron). compress the packing, rotate the screw symmetrically, and do not skew. When manufacturing, we should not only 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 of the valve stem and the valve disc fails: 

Most of the gate valves are using the rectangular head valve stem to connect the T-shaped groove gate disc. Sometimes the T-shaped groove is not processed, so the rectangular head of the valve stem wears quickly. 

This issue can be handled mainly from the manufacturing aspect. However,the user can also reprocess the the T-shaped groove to make it smooth; 

The disc of the double disc industrial valve cannot be pressed tightly against the cover: 

The tension of the double plate 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;