Keywords: Butterfly Valve, Heavy Hammer, New Technology Application
The heavy hammer butterfly valve is a sophisticated device composed of several key components, including the butterfly valve body, hydraulic bypass valve linkage, heavy hammer, release mechanism, manual or electric pump, rack drive cylinder, and an electronic control system (see Figure 1). The system operates by directing pressurized oil from the oil pump into the rack drive cylinder. This causes the piston to move, driving the gear on the main shaft of the butterfly plate and rotating it open. As the butterfly plate opens, the weight is lifted to its highest position. A pawl on the weight locks it in place via the release device, which is controlled by an electromagnet and holding mechanism. In the event of an accident, the electronic control system triggers the release of the electromagnet, allowing the heavy hammer to fall and rotate around the axis, thereby automatically closing the butterfly valve.
The hydraulic system employs a two-stage throttling mechanism to regulate the closing speed of the valve. During the initial stage, the closure is slow to reduce the rate of speed increase, while in the second stage, the closing speed is gradually increased to control the rise in water pressure. This process is illustrated in Figure 2.
One of the key technical features of this valve is its dual-purpose hydraulic system, which allows for compact design and ease of operation. It can also function without external power supply by relying on gravity storage for shutdown. The system automatically closes in case of over-speed, bearing overheating, or generator demagnetization, offering automatic protection to the unit. It also features two-stage closure, ensuring safe and reliable operation with low operating force due to the electromagnet-controlled locking mechanism.
As an example, the D741-10 heavy hammer butterfly valve has the following main technical parameters: pressure rating of 1 MPa, diameters ranging from φ400 to φ1200 mm, maximum head of 100 m, and a working head of 145 m. The opening time is approximately 5 minutes manually or 1 minute electrically, while the closing time includes a fast-closing phase of 5–10 seconds and a slow-closing phase of 10–50 seconds. The over-speed protection range is adjustable up to 1.8 times the rated speed.
This type of valve has been successfully applied in hydropower plants such as the Chaitan Hydropower Plant in Linhai City, Zhejiang Province, and the Pingyang Hydropower Plant. These installations use two D741X-10 heavy hammer butterfly valves. The power station is a hybrid type with a pressure tunnel of 1100 meters and a diameter of 2.6 meters, along with a pressure pipe of 50 meters and 1.2 meters in diameter. The design head is 45.5 meters, with a maximum head of 47 meters and a design flow of 1.8 m³/s. The turbine model is HL220-WJ-50A, and the generator is SFW-630-6/990 (reactive shunt excitation), with a rated voltage of 400V and capacity of 630 kW at 1000 rpm. Since being connected to the grid in January 1991, the two units have operated for a total of 7780 hours.
The heavy hammer butterfly valve has performed reliably, with a 100% correct operation rate after 203 openings and closings. The average electric opening time was 55 seconds, with a fast-closing time of 5 seconds and a slow-closing time of 20 seconds. During accidents, if the unit exceeds 1.4 times the rated speed, the speed measuring device triggers the automatic release of the heavy hammer, closing the water inlet valve and preventing further damage, thus enhancing operational safety.
In conclusion, the heavy hammer butterfly valve significantly improves equipment reliability and ensures safe shutdown. It reduces the labor intensity for operators and lowers maintenance workload. For instance, two units saved four on-duty staff members annually, resulting in about 80,000 yuan in savings. Additionally, the valve can automatically trip when there's no power supply, eliminating the need for backup DC systems. In some power plant designs, where it’s challenging to find an appropriate guide vane closing time under given conditions, the two-stage closure of the heavy hammer butterfly valve offers a more economical and reliable solution compared to artificial resistance or surge control.
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