The main valve of the water inlet valve was originally a gate and a water inlet Sluice Gate, but the main disadvantage of the gate is that the closing speed is slow, and the staged speed adjustment during the closing process cannot be realized. Instead of the hydraulic check butterfly valve, with the development of science and technology, the requirements for the function of the inlet valve group, the hydraulic ball valve has also become the main selection target of the inlet valve in recent years. But now each country chooses a butterfly valve or a ball valve for the main valve of the turbine, and there is no clear requirement in the standard, under what working conditions to choose the butterfly valve inlet main valve or the ball valve inlet main valve. my country’s national standard for inlet valves: basic technical conditions for inlet valves of large and medium-sized turbines GB/T 14478-2012, and there is no specific requirement for selecting butterfly valves or ball valves as the main inlet valve for any working conditions.
It is only required that the diameter of the main inlet butterfly valve is 1000-10000mm, and the diameter of the main inlet ball valve is 500-5000mm.
Based on the experience in valve production and use accumulated by our company over the years (including inheriting the original Tieling Valve Factory for more than 80 years), we will briefly describe how to select and rationally apply the main water inlet valve of the turbine.
As a kind of mechanical equipment, the main function of the valve is to divert, cut off and adjust. The main water inlet valve of the turbine is a kind of valve, and its function is also as described above. At present, the water inlet valves in practical application are mainly butterfly valves, and in recent years, ball valves are also used in working conditions. If only from the history of valve development, the ball valve is one of the oldest valves, with a wide range of applications and mature technology. Compared with the ball valve, the butterfly valve is a new product, and the production history of the butterfly valve is only more than 100 years ago. The butterfly valve and ball valve (including the plug valve) are actually the same ancestors – 90° rotary open and close valve. A butterfly valve is a new type of valve invented to meet the actual working conditions that the ball valve cannot meet. Once it came out, it immediately got very good applications all over the world. (The predecessor of our factory: Tieling Valve Factory was the factory that produced the first butterfly valve in China in the 1970s).
As a kind of high-quality valve, the ball valve has the advantages of good circulation (flow resistance is close to zero) and reliable sealing, but its disadvantages are small diameter (generally below DN1000), large weight (volume), high processing difficulty, and inconvenient maintenance. The important thing is that the ball valve can only realize the function of opening and closing, and cannot be used as a regulating device.
The butterfly valve is a kind of valve invented according to the structure principle of the ball valve, taking its advantages and avoiding its disadvantages. It has a simple structure, convenient processing, reliable sealing, and is lightweight (the weight of the same specification is 1/3-1/5 of the ball valve). It can be manufactured with a large diameter (the largest diameter produced by our factory is DN4500). It has the advantages of convenient maintenance and so on.
The following is part of the selection of the butterfly valve or ball valve for the main water inlet valve of the turbine for the Xinjiang XXX hydropower station project. for reference,
Xinjiang XXX hydropower station project, the actual pressure is 350M head. The caliber is DN2300. The valve parameter is DN2300 PN40. The design institute selects the main valve as a ball valve. Our company recommends that the main valve be a butterfly valve. The specific reasons are as follows:
1. Actual application conditions.
There are very few factories that have actually produced ball valves with such a large diameter of DN2300 PN40. There are very few reference data documenting actual applications. The butterfly valve is the main valve and our factory has produced DN4000 caliber. Other butterfly valve companies may have produced larger diameter ones, and have specific actual operating experience and usage data for reference.
2. Operating costs.
The preliminary calculation of the cost of the ball valve of DN2300 PN40 is equivalent to 5-10 times that of the butterfly valve of the same specification. This does not include its transportation, installation, and maintenance costs. In theory, the advantage of the ball valve is only that the flow resistance coefficient is smaller than that of the butterfly valve, nothing more. As for the main inlet valve, most of the potential energy consumption of water is on the turbine. 70% of the water potential energy is converted into electricity, and the remaining part is basically consumed in pipes and other heat conversions, and the energy consumption in the valve is less than 10%. Therefore, the flow resistance coefficient of the main valve of the turbine can be ignored (just compare the butterfly valve and the ball valve). This is only described for the normally open main valve. If it is a seasonal power generation unit, the advantages of the butterfly valve are more obvious.
3. Influence of main valve performance on pipelines and turbines
As mentioned above, the advantage of the butterfly valve is that it can be used for adjustment. We all know that the function of the inlet valve is only to open and close, and it does not involve adjustment. However, due to the large diameter of the water inlet main valve of the turbine, the opening and closing time will be very long (about 1-5 minutes). Since the ball valve has no adjustment function, it will cause huge turbulence during the opening and closing process. At the same time, due to the flow rate Fast (about 10m/s) will also be accompanied by severe vibration (such a large-diameter ball valve is more obvious). This will cause some damage to the valve block, piping, and turbine. Butterfly valves do not cause the above mentioned situations due to their good regulating function (valve opening and closing process, no or little turbulence is formed).
4. Environmental factors
Xinjiang is located deep in the northwest inland, with large temperature differences between the four seasons, drought, and little rainfall. The environment is relatively harsh. Due to the complex structure of large-diameter ball valves, there are many parts and strict requirements. In harsh environments, the probability of damage to components must be high, and maintenance is difficult. At the same time, due to the large weight of the ball valve itself, the size requirements are strict, and the basic seismic resistance requirements are very high. This also brings a lot of difficulties to installation, commissioning and operation, and maintenance. In contrast, butterfly valve manifolds are easy to maintain due to their lightweight, simple structure, and easy maintenance. Compared with the ball valve manifold, it has incomparable advantages.
In the end, according to the specific working conditions of Xinjiang XXX Hydropower Station, from our company’s production experience over the years and the feedback of actual valve application conditions, we suggest that the water turbine inlet valve uses a butterfly valve as the main valve, which is scientific, reasonable and supported by statistical data.
Application of ball valve:
As an excellent valve type, the circulation advantage of the ball valve is irreplaceable by other valves. It is mainly used in special working conditions such as oil, natural gas, and chemical industry, and is suitable for long-distance pressure transmission pipelines. Its low energy consumption and high circulation effect are very excellent, especially for gas transmission. When the ball valve is fully opened, it can ensure the invariance of gas volume as the same as the pipe diameter, which is very good for the stable temperature control and anti atomization condensation effect of chemical gas.
Application of butterfly valve:
As an alternative product of the ball valve, the above performance of the butterfly valve is far better than that of the ball valve, but its lightweight, simple and universal effect is better than that of the ball valve. It is most suitable for pipeline application of water medium. The application conditions are mainly non-long-distance gathering circuit pipelines, such as condensation system of the thermal power plant, water plant, hydropower station, sewage treatment plant, and civil facilities.