Talking about the Current Situation and Development of China's Drainage Valve Market

Infrastructure construction is the focus of China's economic construction. Water supply and drainage works, especially large-scale sewage treatment projects, have formed a strong water industry in the water treatment equipment manufacturing industry, including pipelines and valves. Provide a good opportunity for the development of the valve industry. China has entered the WTO, the global annual demand for about 3 million tons of valves. To make full use of the valve industry is labor-intensive, poor labor conditions, China's low per capita wages, the advantages of developed countries to transfer production to developing countries, and actively go to the platform of the world economy. Several topics briefly describe the status and development of water supply and drainage valves.

At present, there are about 3,000 large and small-sized valve factories, including 600 in Wenzhou, nearly 200 in Zhengzhou, 150 in Shanghai, 250 in Liaoning, and more than 200 in Jiangsu and Fujian. Although the products are mixed, the product variety has reached more than 3,000. Models, nearly 30,000 specifications. There has been considerable progress in variety of products, sealing performance, strength requirements, adjustment functions, action performance and flow performance, especially sealing performance. Ten years ago, the authoritative source of the Water Supply Association had a saying saying “Ten Valves Nine Leaks, although somewhat exaggerated, is indeed a fact.
The numerous problems that existed in the valve industry were mainly due to the rapid expansion of the market after the reform and opening up, and the original state-owned valve companies were shut down and switched. The level of the mechanical industry was not high, and township and village enterprises (private enterprises) developed rapidly. , The starting point is low, the technical force is very weak, the equipment is simple, most products are imitating production, coupled with market chaos, especially the low-pressure valve for water supply and drainage, the problem is serious. In the past decade, driven by a small number of valve companies, there have been notable advances. Hong Feng concluded that some varieties even reached the international advanced level, and many companies have started their second ventures. But on the whole, there is still a big gap and there is a lot of work to be done. Therefore, it is of great significance to make technical progress and development plans for 2010 and 2020 respectively.

Commonly used valves are widely used in water supply and drainage projects, especially low-pressure and large-diameter valves (low-pressure valves refer to valves with a nominal pressure of PN ≤ 1.6MPa), while medium-pressure valves (PN2.5−6.4MPa) are less. Gate valves and butterfly valves are the most basic and widely used leading products.

2.1 Status Quo and Development of Gate Valves Gate valves have been used for the longest time and have been applied in various countries around the world, especially below DN300mm, and still occupy a dominant position in various types of valves. Its characteristic is that the pressure difference between the front and the back of the valve plate makes the valve plate forcedly press on the valve seat on the right side of the outlet, and the sealing performance is good. When the valve is fully opened, the pressure loss is small because the valve plate is not left in the flow path. Used to cut off the medium in the pipeline.
The disadvantage is that the operating torque is large, and the valve body and the valve stem are easily damaged during operation, especially the large-diameter gate valve. Dimensions and weight are also large, DN1000 caliber gate valve is about 3200mm high, requires four people to operate, so the gate valve is generally used in a small diameter, that is, DN500 below.
Gate valve from full open to the middle opening, the valve flow resistance is small, close to fully closed, the flow resistance increased dramatically. In the larger range, the flow resistance changes little. When the flow is close to full closure, the flow rate changes greatly and must not be used when the valve is closed. It is difficult to fine tune the flow rate at this time. If the opening of the valve is extremely small and the flow rate at the opening is extremely fast, cavitation will be generated at the lower side of the gate, accompanied by intense vibration and noise. The long throttle operation will often cause the valve body and gate metal to occur. Cavitation. If the working condition of the gate valve is in the middle opening, the valve plate is supported by the guide rails on both sides. When the valve plate is fully closed, the valve plate is tightly fitted. In the intermediate position, the valve plate and the guide rail have a large gap and generate vibration. Therefore, Hong Feng believes that even in areas with low incidence of cavitation, long-term operation of the valve throttling, the guide rails will be deformed, worn or damaged, and the contact surface pressure is high because the valve seat is not in full contact. Cramping or sticking tends to occur, so it is not suitable for flow control. Also note that when the gate valve is at a small opening, the flow rate changes greatly. If the valve is opened and closed in an emergency, the pressure will rise sharply or generate negative pressure, especially when the valve is closed.

On the basis of metal-sealed gate valves, rubber soft-seal gate valves have been developed in recent years. Their characteristics are:
(1) There is no recess at the bottom of the body of the body, and the fluid passes through the cross section in a straight line, and it is not easy to accumulate and inclusion foreign matter.
(2) The sealing surface of the gate is pressed against the valve body to stop water, and the valve closing torque is small.
(3) The sealing performance is not affected by the bending and stretching of the piping.
(4) The entire valve plate lined with rubber, corrosion resistance, no rust.
(5) The valve can replace the sealing material and the O-ring while fully opening the water.
(6) Gates are interchangeable.
Due to its superior functions, Hongfeng sees a rapid increase in international demand (especially in Europe). The soft seal gate valve was invented by Austrians 30 years ago. It produces more than 500,000 units per year in Europe and is used almost 100%. It is a hard-sealed gate valve. For alternative products, the manufacturing caliber is DN500 in Europe and Japan, DN400 is generally used in the United States, and DN1200 is produced in Italy. But there are also defects. The soft seal gate valve is compressed and sealed by the rubber seat. Avoid closing the valve too tight, do not exceed the closing valve torque as well (torque given in the standard).

2.2 Status Quo and Development of Butterfly Valves Hong Feng remembers that in the 1930s, the United States invented the butterfly valve and introduced it to China in the 1970s for development and use. At present, the butterfly valves in the world generally have replaced the gate valves above DN300mm. Compared with the gate valve, the butterfly valve has the advantages of short opening and closing time, small operating torque, small installation space and light weight. Take DN1000 as an example, the butterfly valve is about 2T, and the gate valve is about 3.5 T. The butterfly valve is easy to combine with various driving devices and has good durability and reliability.
The disadvantage of the rubber seal butterfly valve is that if it is used for throttling, cavitation may occur due to improper use, and the rubber seat may peel off or be damaged. For this reason, in the seventies and eighties of the last century, metal-sealed butterfly valves were developed in the world, which have cavitation resistance and long life. In recent years, China has also developed metal-sealed butterfly valves, but pay attention to the valve body, valve seat, and valve plate. If the material of the valve seat is not suitable for combination, there will be a risk of hot engagement between the valve seats, and they cannot be opened or closed. In addition, cavitation-resistant, low-vibration, low-noise comb-tooth butterfly valves have also been developed in foreign countries. Due to the improvement of casting technology, cast iron valve bodies, valve plates and stainless steel valve seats can be cast together, so that the structure of the valve seat part is simple, the guide material is not accumulated, and durability and reliability are greatly improved. The life of the general seal seat under normal conditions, rubber more than 15 years, stainless steel metal about 80 years, comprehensive comparison of different. However, how to use it correctly must be based on working conditions. The relationship between the opening and the flow of the butterfly valve is basically a linear proportional change. If the valve is in a large throttle state, the back of the valve plate is prone to cavitation, which may damage the valve. Generally, it is used outside 15 degrees. Below the throttle valve will produce negative pressure, rubber seals often appear off. Butterfly valve operating torque, due to opening and valve opening and closing direction of different values, horizontal butterfly valve, especially large-diameter valve, due to water depth, the shaft shaft, the head of the water generated by the torque can not be ignored. In addition, when the elbow of the inlet side of the valve is deflected, the bias flow will increase and the torque will increase.

2.3 Exhaust Valves Due to the small exhaust capacity and other reasons, the old two-port exhaust valves have gradually been replaced by new high-speed intake and exhaust valves. Judging the performance of the exhaust valve in addition to the general requirements of the valve, there are three important points:
(1) The large orifice closes under most pressure differences.
(2) The medium in the pipeline: water, whether the ball will be pressed when rushed up and the orifice cannot be closed.
(3) Whether the seal is still leaking at low pressure (0.02 MPa).
The choice of exhaust valve diameter needs to be cautious, especially when negative pressure is generated in the pipe, it needs to be supplemented so that the negative pressure in the pipe does not exceed 0.35 kgf/cm2, otherwise the pipeline will be unstable and damaged.
Problem of stopping special pump for water hammer protection

3.1 Types of Water Hammers Water hammers can be divided into four types from different angles. The relationship between valve closing duration and water hammer phase μ can be divided into direct water hammer and indirect water hammer. According to the external conditions of water hammer, it can be divided into starting water hammer, closing valve water hammer and stopping pump water hammer; The characteristics can be divided into two kinds: rigid water hammer theory and elastic water hammer theory. According to the phenomenon of water hammer fluctuation, it can be divided into water column continuous phenomenon and water column separation water hammer phenomenon.
According to survey statistics, the majority of water hammer accidents in the water supply and pumping stations of urban water supply and industrial enterprises are related to the accident of pumping water hammer. Water hammer accidents are very harmful and cause sudden bursts of pipes and equipment. Since this article only deals with the protection of water hammers that stop pumps, the theoretical issues of water hammers are discussed separately. The end of the general pipe closing valve water hammer is the first high pressure, after the occurrence of low pressure. The feature of pumping water hammer in the pumping station is that the high pressure occurs after the low pressure occurs first, and because the rotating part of the water pump motor has a certain moment of inertia, the speed is gradually reduced after the power outage, but the speed is gradually reduced, and the water pump is still in working condition. Both the head and the water are gradually reduced. When the head falls to the pressure of the external pipeline and the flow rate becomes 0, the water starts to flow backwards. At this moment, the water pump is still being turned by the reverse flow, and the speed drops quickly. This stage is the braking phase. Further, when the speed of the water pump is 0, it is reversed, pushing the pump to reverse, and it starts to enter the working state of the turbine, and then the pressure gradually rises. The duration of the entire low pressure (or negative pressure) water hammer wave is greater than the normal water hammer wave. Low pressure (or negative pressure) wave time, generally from 4, 5 seconds to 7, 8 seconds. When the pump outlet does not have a check valve, the water can be pumped back through a large number of backflows after the pump is stopped, so that the pressure of the positive pressure water hammer is effectively reduced. Therefore, under certain circumstances, water hammer can be eliminated to prevent water hammer accidents, but Can not eliminate the water hammer pull off the water column. When the outlet of the pump is equipped with a check valve or the outlet valve of the pump is closed earlier, the water can impinge on the check valve to close quickly after the water flows backwards, thereby generating a larger water shutoff valve, especially when the water hammer is pulled off the water column. The return water column hits the check valve of the closing valve and will generate a great water hammer pressure, which is our main protection object. Stop pumping water hammer protection valve to adapt to the characteristics of this process production and manufacturing, and in normal operation, the head loss should be small, safe and reliable. If the pipeline is assumed to be a rigid body, the water hammer pressure type g: gravity acceleration m/s;
a: water hammer wave propagation speed, approximately 1000m/s;
V: flow rate m/s;
L: pipe length m.
The direct water hammer occurs when the pipeline is longer and the valve closing speed is faster. Therefore, the control of the valve closing time T is very important and should be satisfied.
3.2 valve cavitation problems with the cavitation coefficient δ value to select when used as control flow, select what kind of valve structure type H1: valve (outlet) pressure m;
H2: the difference between saturation vapor pressure corresponding to atmospheric pressure and its temperature, m;
ΔP: differential pressure m before and after the valve;
The rest of the symbols are the same as before.
Due to the different structures of various valves, the allowable cavitation coefficient δ is also different. If the calculated cavitation coefficient is greater than the allowable cavitation coefficient, it is available and no cavitation will occur. If the butterfly valve allows a cavitation coefficient of 2.5, then:
If δ > 2.5, cavitation does not occur.
When 2.5>δ>1.5, slight cavitation occurs.
When δ<1.5, vibration occurs.
When δ < 0.5 continues to be used, it will damage the valve and downstream piping.
3.3 Hygienic Requirements for Valves The requirements for hygiene and epidemic prevention of tap water pipes and valves are very important. At present, no attention has been paid to all aspects of production, construction, and application. Various medicines and foods have now been strengthened in management, but people are most exposed to daily However, few people are interested in the water. The future is an important issue that we should solve. GB5749 "Sanitary Standards for Drinking Water" and GB/T17219 "Evaluation Criteria for Safety of Drinking Water Distribution Equipment and Protective Materials for Drinking Water" shall be strictly enforced. There must be certification from the provincial-level or above sanitation and epidemic prevention department, and 21 items stipulated in the soaking test. And the other three projects, the coatings should be tested for the hygiene requirements of 21 prescribed projects and 5 other projects. Raw materials reach food grade.

3.4 Valve protection problems Hongfeng believes that the valve life should be extended to ensure the sanitary requirements of the valve. The metal surface of the valve must be painted. The thickness of the coating must be ensured. The coating process must be performed before the surface treatment of the metal to reach the level (near white Grade), and thermal spraying is recommended. The outer surface of the open-air valve should be coated with UV-resistant acrylic paint.
Not only the above problems need to be solved, but also the flow coefficient should be optimized to reduce the head loss coefficient, and research should be conducted to improve the production technology of special valves for large-scale pressure regulation and flow adjustment (energy dissipation), such as needle valves (piston valves), porous valves, Ring spray valve (fixed poppet valve), water barrier with guaranteed diversion preventer, etc., and further development of large-scale butterfly valve (DN3000 above) and so on.