Valve repair procedures and common failure prevention valve standard system

Valve repair procedures and common failure prevention valve standard system

Troubleshoot the detected problems. Valve body defect repair welding. Hardfacing or renewing the sealing ring. Straighten or replace stem. Repair all other parts that should be repaired; Replace those that cannot be repaired. Reassemble the valve. When assembling, gasket and packing should be replaced completely. Conduct strength test and sealing test. When pressing the packing, the force is not uniform, or the gland is defective. Press the packing, turn the screws symmetrically, do not deviate. When manufacturing, we should not pay attention to large and key parts, but also pay attention to the secondary requirements such as gland, otherwise it will affect the use.
General procedure for valve repair
When the valve is dismantled, the steel word is on the valve and the flange connected with the valve, and the maintenance number is played, and the working medium, working pressure and working temperature of the valve are recorded, so that the corresponding materials are selected when repairing. When repairing the valve, it is required to be carried out in a clean environment. First clean the outer surface of the valve, or blow with compressed air or clean with kerosene. But remember nameplates and other signs. Check for external damage and record. Then disassemble the other parts of the valve, clean it with kerosene (not with gasoline, so as not to cause a fire), check the damage of the other parts, and make a record. Strength test body bonnet. Such as high pressure valves, but also for non-destructive testing, such as ultrasonic testing, X-ray testing.
The sealing ring can be used red red powder inspection, seat, gate (valve do) degree of anastomosis. Inspect stem for bending, corrosion and thread wear. Check stem nut wear.
Troubleshoot the detected problems. Valve body defect repair welding. Hardfacing or renewing the sealing ring. Straighten or replace stem. Repair all other parts that should be repaired; Replace those that cannot be repaired. Reassemble the valve. When assembling, gasket and packing should be replaced completely. Conduct strength test and sealing test.
Common valve failure and prevention
(a) general valves
1, stuffing box leakage
This is the main aspect of running, running and leaking, which is often seen in factories. The causes of stuffing box leakage are as follows:
1, packing and working medium corrosive, temperature, pressure is not suitable;
2, the filling method is not correct, especially the whole packing in reserve rotation, ** easy to produce leakage;
3, the valve stem processing accuracy or surface finish is not enough, or ellipticity, or notch;
4, stem has pitting, or rust due to lack of protection in the open air;
5, stem bending;
6, packing has been aging after too long use.
7, the operation is too fierce.
2. Leakage of closing parts
Figure 5-4 Schematic diagram of sealing surface leakage
Figure 5-5 Leakage diagram of sealing ring root
Usually the stuffing box leakage is called leakage, the leakage of the closing part is called leakage, leakage of the closing part, in the valve, is not easy to find. Leakage of closed parts can be divided into two categories; One is leakage of sealing surface (as shown in Figure 5-4). The other is leakage of seal root (as shown in Figure 5-5)
Causes of leakage are:
1, sealing surface grinding is not good;
2, the sealing ring and valve seat, valve do not fit tightly;
3, the valve office and stem connection is not reliable;
4. The valve stem is bent and twisted to make the upper and lower closing parts misaligned;
5, close too fast, the sealing surface contact is not good or has been damaged;
6, improper material selection, can not withstand the corrosion of the medium;
7, the globe valve, gate valve for adjustment use, sealing surface can not withstand the impact of high-speed flowing medium;
8, some media, cooling gradually after the valve is closed, so that the sealing surface crack, will also produce erosion phenomenon;
9, some sealing ring and valve seat, valve office between the thread connection, easy to produce oxygen concentration battery, corrosion loose;
10, due to welding slag, rust, dust and other impurities embedded, or the production system has another piece of machinery off the valve core, so that the valve can not be closed.
3, the valve stem lifting failure.
The reasons are as follows:
1. Excessive operation causes thread damage;
2, lack of lubricant or lubricant failure;
3. Stem bending and torsion;
4, the surface finish is not enough;
5, with tolerance is not allowed, bite too tight;
6, stem nut tilt;
7. Improper material selection; For example, stem and stem nut for the same material, easy to bite;
8, thread wave medium corrosion (refers to the dark stem valve or valve stem in the lower valve);
9. The open valve is lack of protection, the stem thread is covered with dust and sand, or corroded by rain, frost and snow.
4 other
Valve body cracking: generally caused by freezing. When the weather is cold, the valve should have thermal insulation measures, otherwise after production should be the valve and connecting pipeline water drainage net (such as valve bottom wire blockage, can open the wire blockage drainage).
Handwheel damage: impact or long lever force operation. It can be avoided by the attention of the operator or other concerned personnel.
Breakage of packing gland: uneven force or defect of packing gland. Press the packing, turn the screws symmetrically, do not deviate. When manufacturing, we should not pay attention to large and key parts, but also pay attention to the secondary requirements such as gland, otherwise it will affect the use.
Stem and gate connection failure: the gate valve uses stem square head and gate t-groove connection in many forms, t-groove is sometimes not processed, so that the stem square head wear faster. Mainly from the manufacturing aspect to solve. But the use of units can also fill the T slot processing, so that she has a certain degree of finish.
Double gate valves do not compress the face: Double gate tension is generated by the top wedge. on some gate valves, the top wedge is of poor material (low grade cast iron) and will wear or break after use. The top wedge is a small piece, replaced by the original cast iron.
(two) automatic valve
1, spring safety valve
One of the faults is leakage of sealing surface. The reasons are as follows: (1) there are sundries between sealing surfaces; Sealing surface damage. This kind of trouble should be prevented by regular maintenance. Second, the sensitivity is not high. The reasons are: (1) spring fatigue; ¢Ú Improper use of spring. Spring fatigue, no doubt should be replaced. Improper use of spring, is the user does not pay attention to a nominal pressure spring safety valve, there are several pressure sections, each pressure section has a corresponding spring. If the nominal pressure is 16 kg/cm 2 safety valve, the use of pressure is 2.5 ~ 4 kg/cm 2 pressure section, installed 10 ~ 16 kg/cm 2 spring, although also can make do, but suddenly high suddenly low, very insensitive.
2, check valve
Long see faults are: (1) disc broken; ¢Ú Medium backflow. The reason for breaking the valve office is that the medium pressure before and after the check valve is in a state of balance and mutual “see-saw”. The valve office often beats the valve seat, and some brittle materials (such as cast iron, brass, etc.) made of the valve office is broken. The method of prevention is to use check valves made of ductile materials.
The reasons for media backflow are: (1) sealing surface damage; ¢Ú Insert impurities. Backflow can be prevented by repairing sealing surface and *** impurities.
The above description of common faults and prevention methods, can only play an inspiring role, in actual use, there will be other faults, to be active and flexible to prevent the occurrence of valve failure, the most fundamental is to be familiar with its structure, material and action principle.
Valve standard system the valve standard system is very complex, mainly by the basic standard, material standard, product standard, method standard and so on. In modern international trade, technical standards have become the main non-tariff technical barriers between countries. China has gradually formed a relatively perfect valve standard system, but there is still a big gap compared with Europe and the United States and other developed countries. Valve standard system can be divided into three levels: *** layer for the basic standard and method standard. The second layer is product standards. The third layer is parts and materials standards.
1. Valve standard system
The valve standard system is very complex, mainly composed of basic standard, material standard, product standard, method standard and so on. In modern international trade, technical standards have become the main non-tariff technical barriers between countries. China has gradually formed a relatively perfect valve standard system, but there is still a big gap compared with Europe and the United States and other developed countries.
Valve standard system can be divided into three levels: *** layer for the basic standard and method standard. These standards are comprehensive standards, usually applicable to all kinds of industrial valves, the standard level is based on national standards; The second layer is product standards. These standards are basically determined by valve structure classification, specifying the types, performance parameters and manufacturing inspection requirements of various valves and valve drivers. The layer standard can be defined as national standard and industry standard according to its scope of use. Product standards can also be classified according to the use, including chemical industry, petroleum industry, water supply system, etc., but such classification is not scientific, easy to cause the repetition and confusion of standards. Therefore, the system is mainly classified according to the structure of products; The third layer is parts and materials standards. These standards serve or are assigned to product standards. Parts and components standards are based on industry standards. China’s valve standard system concrete block diagram.
2. Domestic common valve standard code
GB National Standard
JB Machinery industry standard
HG Chemical industry Standard
SY Petroleum industry standard
SH Sinopec Corporation standard
EJ Nuclear industry standard
CB Shipbuilding Corporation standard
DL Power Industry Standard
QT light industry standard
Note: The code name of the recommended standard is “/T”, for example, the code name of the national recommended standard is “GB/T”.
3. Foreign common valve standard code
ISO International Standard
ANSI American national standard
API American Petroleum Institute standard
ASTM Standard of American Society for Materials and Testing
AISI American Institute of Iron and Steel standards
MSS American Association of Valve and Pipe Fitting Manufacturers standards
AWWA American Watercourse Treatment Association standard
AWS AWS Standards
ASME Standards
EN European Community standard
DIN German national standard
BS British National Standard
NF French national standard
JIS Japanese national standard
JPI Japan Petroleum Institute standard
¦Ã OCT is the former Soviet State standard
Valve development history
(a) the development course of China’s valve industry
Since the founding of the People’s Republic of China, the valve industry has gone through a difficult course. Valve manufacturing from repair, handicraft based sporadic processing to special aircraft, production lines, NUMERICAL control, processing center mass production; Production design from copying to independent research and development; Product standard system from scratch, and then with basic standards, material standards, product standards and product test inspection relatively sound standard system; Product performance from low pressure normal temperature to medium pressure, high pressure, ultra high pressure high temperature and low temperature, perfect temperature conditions; Varieties from general valves to all kinds of ** * valves, a variety of materials, a variety of driving modes of all kinds of special valves, and has strong supporting ability. The size of the valve industry is also from small to large, manufacturers in the country and the layout is more reasonable, formed a sound valve manufacturing system, made a great contribution to the development of the national economy.
In the early days of the founding of the People’s Republic of China, there were a few small factories engaged in valve repair and production of low-pressure valves. In 1949, the valve output was 387 tons. In 1956, high pressure valves began to be mass-produced. In 1958, a large number of professional valve manufacturers emerged. After the establishment of valve industry organization in 1960, under the support of the ministry bureau began to develop greatly. By the end of 1984, there were 161 valve factories above county level in the machinery industry system with 90,743 employees, including 66,721 production workers and 3,563 technical personnel.
After 1984 (the third Plenary Session of the Eleventh Central Committee of the Communist Party of China), the valve industry has changed a lot, valve production is also moving forward and developing on the road, valve private enterprises have developed rapidly, some state-owned enterprises began to transform, gradually from the state ownership of limited liability company, stock cooperative system and individual management. Shenyang high pressure valve factory, Lanzhou high pressure valve factory, Kaifeng high pressure valve factory, Shanghai valve factory, Shanghai Lianggong valve factory, Beijing Valve Factory, was first bought out by Shenzhen Rheinda Company, and then transformed into Shenyang Shengshi high pressure valve Co., LTD., Shanghai valve factory was contracted by wenzhou, Shanghai lianggong valve factory, zigong high pressure valve factory and a number of domestic state-owned enterprises have been restructured. The valve industry has formed a new pattern, in Yongjia oubei town and Wenzhou Longwan district to form a new valve production base, at the same time in Henan, Shanghai, Hebei, Jiangsu and other places also formed a more concentrated regional valve manufacturing base.
According to incomplete statistics, as of the end of 2008 domestic valve enterprises about 4000 valve factories, including more than 1000 wenzhou area, henan Zhengzhou nearly 300, Shanghai more than 200, Liaoning 250, Jiangsu, Fujian each more than 500, although the good and bad are mixed, but product varieties have reached more than 3000 models, nearly 30,000 specifications.