Large-diameter Telescopic Hydraulic Slow Closing Butterfly Valves (Part Two)

Large-diameter Telescopic Hydraulic Slow Closing Butterfly Valves (Part Two)


4. The calculation of the opening and closing torque of the valve
After the main structure of the valve and the supporting and sealing structure at both ends of the valve body are determined, the maximum dynamic water force can be calculated. The maximum dynamic water moment and the combined torque both occur when the valve is close to closing. The opening and closing torque of the heavy hammer hydraulic control butterfly valve is calculated as follows:
(1) Take a centrifugal pump as an example. There is water behind the valve. First, open the pump and then open the valve. Open the valve after the pump reaches the rated pressure. At this time, the pressure before the valve is the pressure at zero flow of the pump, and the pressure after the valve is the geometric lift pressure of the pump station. The valve opening torque is:
 
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In the formula, MC is the friction torque at the bearing at both ends of the valve shaft, N•m. MT is the friction torque between the valve shaft and the sealing packing, N•m. MM is the friction torque of the valve body diameter and sealing surface, N•m. MH is the resistance torque of the valve hydraulic system, N•m. MG is the heavy hammer moment, N•m. θ is the angle between the heavy hammer connecting rod and the axis of the pipeline when the valve is fully closed.
 
(2) There is no water behind the valve. Open the pump first and then open the valve. At this time, the pressure before the valve is the pressure at zero flow of the pump, and the pressure after the valve is zero. At this time, the operating torque is the smallest, and its value is:

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The above calculation shows that the designed hydraulic working torque should be greater than the maximum operating torque and the safety factor should be considered in order to reliably open the valve. The valve opening procedure is to open the pump first and then open the valve, and in order to prevent the pipeline's water hammer from boosting pressure and control the reverse of the pump impeller. The closing procedure is to close the valve first and then stop the pump.
 
5. The hydraulic control system of the valve
(1) The hydraulic system of the valve includes hydraulic components such as swing cylinders, accumulators and solenoid valves.
(2) The swing cylinder is the driving mechanism for opening the valve and the braking damping mechanism when the valve is closed. The angle regulating valve and the speed regulating valve adjust and control the opening and closing speed and the fast and slow closing angle of the butterfly valve.
(3) The accumulator is the power source for opening and closing the butterfly valve. The energy of the accumulator is provided by the motor and the oil pump. At the same time, the accumulator, the digital display pressure controller and the oil pump form an automatic pressure storage and energy storage closed-loop system, which can stabilize the system. If the system pressure drops below the set value, the oil pump will automatically start to supply pressure to the accumulator.
 
6. The electrical control system of the valve
The electrical control system is divided into two types, that is, ordinary relay control types and PLC intelligent control types. Ordinary relay control logic operation is realized by relay. It can not only operate directly, but also can be connected to the DCS system to realize remote control and direct state switching with universal switches. The remote signals that can be received are opening of valves, closing of valves, stop, status of water pumps and pipeline pressure. The output signals for remote DCS monitoring are opening position signals of valves, status signals, status signals of oil pumps, lock status signals, fault signals and 4 to 20mA analog signals, except the valve status 4 to 20mA signal; the rest of the signals are passive dry contact switching signals.
 
PLC intelligent control logic operation is realized by programmable controller PLC, which not only improves the reliability of system logic operation, but also is simple and easy to maintain. At the same time, because of the use of human-machine interfaces such as the expansion of functions, processing text displays and touch screens, it has been fully reflected in the aspect of intelligence.
 
7. Conclusion
The hydraulically controlled slow-closing butterfly valve designed in this article is a kind of pipeline control device, which is mainly installed at the inlet of the turbine of the hydropower station and used as a turbine valve. It can also be installed at the pump outlet of various pumping stations such as water conservancy, electric power, water supply and drainage to replace the function of check valves and gate valves. When working, the valve fast closes, slowly closes, slowly opens, and quickly opens through the preset opening and closing procedures to achieve a reliable cut-off of the pipeline and effectively eliminate the water hammer of the pipeline, which is of great benefit to energy saving, water saving and environmental protection.