This article introduces the performance and composition of the ultra-large intelligent flow control equipment manufactured by FCV Company, discusses the dynamic and static sealing characteristics of the DN4800 butterfly valve designed according to the actual working conditions, and summarizes the rigidity of the main body of the butterfly valve by using a computer. And the method of finite element theoretical analysis of strength and strength to achieve structural optimization design.
Keywords： butterfly valve, structure design, double seal pair, dynamic seal, hydraulic control, heavy hammer.
With the rapid development of the world economy, urban water diversion and electricity consumption have increased significantly year by year, especially for hydroelectric power generation with no pollution and low operating costs. Domestic and foreign hydroelectric power generation projects are increasing year by year, and the equipment specifications used are also increasing. Large-scale intelligent flow control equipment is the key equipment for controlling fluid medium transportation conditions. In hydroelectric power stations, the equipment is installed between the dam and the turbine generator to ensure the normal operation of the turbine and prevent accidents such as runaways from other important equipment in the system. In thermal power stations and water diversion projects, intelligent flow control equipment completes various prescribed actions according to procedures and instructions to prevent water hammers and make the system safe, stable and continuous operation under the best economic conditions. Tieling Flow Control Valve Co., Ltd is a major manufacturer of large-scale flow control equipment. Among them, the complete set of butterfly valves for super-large hydropower stations above DN4000 is a key supporting device, which requires high safety and control complexity.
Valve complete device design
1 . structure
The butterfly valve complete set is mainly composed of upper and lower connecting short pipes, butterfly valves, expansion joints, bypass valves, globe valves, bypass pipes, air valves, hydraulic actuators, hydraulic stations, electric actuators and electrical control cabinets. （Figure 1), the butterfly valve is an important part of it, which cuts off the medium or adjusts the flow and pressure of the medium. The connecting short pipe and the expansion joint play the role of connecting with the main pipe and facilitating disassembly and assembly. The bypass pipe, the bypass valve and the stop valve constitute the bypass system of the main pipe to reduce the pressure difference between the front and the back of the main valve closing part and have a flat pressure effect. Conducive to the opening and closing of the closure and the start of the turbine. The air valve is used to remove the air in the pipeline, and as the air inlet passage when negative pressure is generated in the pipeline, to protect the pipeline from negative pressure instability and avoid excessive water hammer. The hydraulic station is the power source of the hydraulic actuator. The hydraulic or electric actuator drives the valve closing part to move so that the valve completes the specified action according to the program and realizes the predetermined function. The electrical control cabinet is the operating control component, which issues operating instructions and the detection and display of valve working status and its own faults. Complete intelligent automatic control.
1. Connecting pipe 2. Drain manual gate valve 3. Bronze cock 4. Access door 5. Swing cylinder 6. Main expansion joint 7. Connecting rod body 8. Hydraulic butterfly valve 9. Downstream connecting pipe 10. Manual butterfly valve 11. Quick intake and exhaust valve 12. Bypass expansion joint 13. Electric butterfly valve 14. Bypass straight pipe 15. Manual butterfly valve 16. Bypass elbow 17. Upstream connecting pipe 18. Pressure sensor 19. Ball valve 20. O-ring (The hydraulic station and accumulator group are not shown in this figure)
Figure 1 Butterfly valve complete set
2. Technical Features
The main parameters of the butterfly valve complete set are as follows.
Nominal size: DN4800
Working head: 108.83m
Maximum head: 150m
Flat pressure opening: 0.3MPa
Opening and closing time: 60～120s
Water shut-off time: 60～120s
Drive mode: Hydraulic, touch screen PLC integrated control
Sealing structure: Main valve double seal
3. Sealing substructure
The butterfly plate adopts a double-plate truss structure, and a streamlined design is adopted on the front surface to reduce fluid resistance loss and flow resistance. By reasonably selecting the offset value of the double eccentricity of the valve and taking advantage of the feature of low resistance during flat pressure opening, the opening and closing torque design of the driving device is more reasonable, and the service life of the rubber sealing ring and the reliability of the valve are improved. The floating of the butterfly plate sealing ring can be adjusted in any direction, which simplifies the processing and assembly process.
The sealing pair structure is double-disc, double sealing pair, and double eccentric. That is, a sealing pair is designed on the upstream and downstream sides (Figure 2).
(a) Metal dynamic seal pair structure on the upstream side (b) Rubber seal pair structure on the downstream side
Figure 2 Sealing structure
The downstream side seal pair adopts a soft seal pair sealing structure. The sealing ring on the butterfly plate is T-shaped, the material is nitrile rubber, and the leakage can be controlled to zero leakage. This kind of seal is called working seal or static seal for this valve. The structure designed as a double seal pair makes the valve safer in leakage control. The metal seal has a long service life, and the rubber has good sealing performance. The two sealing performances are complementary. At the same time, the metal seal on the upstream side is also to facilitate the replacement of the rubber seal ring on the downstream butterfly plate (the rubber ring is a vulnerable part). Users no longer need to configure maintenance valves when designing the system, reducing the project cost (for DN4800 butterfly valves, a set of maintenance valves is more than one million yuan), and it also facilitates the user’s maintenance. This kind of seal is called a maintenance seal or a dynamic seal. The soft seal on the downstream side is the working seal of the valve, which protects the normal operation of the turbine or pump. The moving metal hard sealing structure on the upstream side can be applied to ordinary large-diameter metal sealing butterfly valves. This structure does not require the valve body and the butterfly plate to be boring together, and the butterfly plate sealing ring can be adjusted arbitrarily. For super large diameter valves, if the upstream side metal hard seal leaks too much, it may cause the medium pressure of the double-disc cavity (the downstream side rubber seal leakage is 0) and the downstream disc seal ring cannot be replaced. According to this situation, the valve body between the upstream side disc and the downstream side disc is designed with a pressure relief external discharge device. The discharge volume is far greater than the leakage volume so that the medium inside the double-disc will not form pressure.
4. Finite Element Analysis
In the design process of main parts such as butterfly plate and valve body, FCV engineers used three-dimensional modeling and finite element stress analysis methods for stiffness and strength analysis (Figure 3), which can make the loading deformation of the main parts within a controllable range. On the premise of ensuring reliable valve sealing and flexible opening and closing, the application of structural materials is more reasonable, and it is close to the equal-strength design.
Figure 3a FCV Finite element analysis diagram of DN4800 hydraulic control butterfly valve body
Figure 3b FCV Deformation analysis diagram of DN4800 double plate butterfly valve
When testing the DN4 800 butterfly valve set device, it strictly follows the requirements of GB, BS, DIN, and other relevant standards, and at the same time meets the user’s parameter requirements. The strength test, action test, control function and parameter test of the valve all meet the corresponding requirements. Its leakage is zero. With the heavy hammer closed, the switching speed of the hydraulic actuator can be adjusted throughout the entire process as required.
The super-large intelligent fluid control equipment can make the fluid delivery system operate continuously and stably for a long time. The service life is more than 40 years, and the service life of wearing parts is more than 5 years. The fluid dynamics design and characteristics of the butterfly valve flow chamber are more optimized, and the flow resistance is more optimized. The coefficient is small, and the action is flexible and reliable. In recent years, water conservancy, hydropower projects, and thermal power plants are developing towards large-scale parameterization. The requirements for super-large intelligent control equipment are increasing, and the application prospects are broad.