The relationship between the opening of the ball valve and plastic valve the flow rate basically changes linearly. If it is used to control flow, its flow characteristics are also closely related to the flow resistance of the piping. For example, two pipelines are installed with the same valve diameter and form, but the pipeline loss coefficient is different, and the flow rate of the valve will also be very different.If the valve is in a state with a large throttle range, the back of the valve plate is prone to cavitation, which may damage the valve. Generally, it is used outside 15°.When the plastic ball valve is in the middle opening, the opening shape formed by the valve body and the front end of the butterfly plate is centered on the valve shaft, and the two sides form different states. The front end of the butterfly plate on one side moves in the direction of the flow of water, and the other side is counter to the direction of the flow. Therefore, one side of the valve body and the valve plate form a nozzle-like opening, and the other side is similar to a throttle opening. The nozzle side has a much faster flow rate than the throttle side, and negative pressure will be generated under the throttle side valve. Rubber seals often fall off.Plastic ball valves and butterfly rods have no self-locking ability.
For the positioning of the butterfly plate, a worm gear reducer must be installed on the valve rod. The use of worm gear reducer can not only make the butterfly plate have self-locking ability, make the butterfly plate stop at any position, but also improve the operation performance of the valve.The operating torque of the plastic ball valve has different values due to the different opening and closing directions of the valve. For horizontal ball valves, especially large-diameter valves, the torque produced by the difference between the upper and lower water heads of the valve shaft due to the depth of water cannot be ignored. In addition, when an elbow is installed on the inlet side of the valve, a bias flow is formed and the torque will increase. When the valve is in the middle opening, the operating mechanism needs to be self-locking due to the water flow torque.The plastic ball valve has a simple structure, consisting of only a few parts, and saves material consumption; small size, light weight, small installation size, small driving torque, simple and rapid operation, only need to rotate 90° to quickly open and close; and At the same time, it has good flow adjustment function and closing and sealing characteristics.
In the application field of large and medium caliber, medium and low pressure, plastic ball valve is the dominant valve form. When the ball valve is in the fully open position, the thickness of the butterfly plate is the resistance when the medium flows through the valve body, so the pressure drop produced by the valve is small, so it has better flow control characteristics. The ball valve has two sealing types: elastic seal and metal seal. Elastic sealing valve, the sealing ring can be inlaid on the valve body or attached to the periphery of the butterfly plate.Valves with metal seals generally have a longer life than valves with elastic seals, but it is difficult to achieve a complete seal. Metal seals can adapt to higher operating temperatures, while elastic seals have the defect of being limited by temperature. If the ball valve is required to be used as a flow control, the main thing is to correctly select the size and type of the valve. The structural principle of the ball valve is especially suitable for making large caliber valves. Ball valves are not only widely used in general industries such as petroleum, gas, chemical, and water treatment, but also used in cooling water systems of thermal power stations.Commonly used ball valves include wafer butterfly valves and flange butterfly valves.
Wafer type ball valves are connected between two pipe flanges with stud bolts. Flange type ball valves are equipped with flanges on the valve. The two ends of the valve are flanged to the pipe flanges with bolts. The strength performance of the valve refers to the ability of the valve to withstand the pressure of the medium. The valve is a mechanical product that bears internal pressure, so it must have sufficient strength and rigidity to ensure long-term use without cracking or deformation.With the application of anti-corrosion synthetic rubber and polytetrafluoroethylene, the performance of the ball valve can be improved and meet different working conditions. In the past ten years, the metal-sealed ball valve has developed rapidly. With the application of high temperature, low temperature, strong corrosion resistance, strong erosion resistance, and high-strength alloy materials in butterfly valves, metal sealed ball valves have been used in high temperature, low temperature, and strong erosion. It has been widely used under other working conditions and partially replaced the globe valve, gate valve and ball valve.
