Butterfly valve is the most widely used valve in wastewater treatment. Its circulation medium includes sewage, clean water, activated sludge, low-pressure gas for aeration, etc. Its maximum flow diameter can exceed 2m. Figure 6-13 is a photo of a stainless steel butterfly valve.
The butterfly valve is composed of valve body, inner lining, butterfly plate and opening and closing mechanism. The valve body is generally made of cast iron, and special ones are also made of stainless steel and plastic, etc. The connection with the pipeline is mostly flanges. The main function of the inner lining is to realize the sealing between the valve body and the butterfly plate, to avoid the contact between the medium and the cast iron valve body and the flange sealing. The inner lining is mostly made of rubber material or nylon material: stainless steel butterfly valve has no amount of inner lining. The movement mode of the butterfly plate is rotation, and the maximum rotation angle is 90°. The material of the butterfly plate is determined by the medium, some are steel materials with anti-corrosion layer or plating, and some are stainless steel or aluminum alloy. The central axis of the butterfly plate is fixed on two sliding bearings above and below the valve body. The opening and closing mechanism is divided into two types: manual and electric. Small butterfly valves can be turned directly by the handle. For larger ones, worm gears are used to decelerate and increase the force. For those with a diameter greater than 500mm, gear deceleration and spiral deceleration must be added in addition to worm gear deceleration. The board rotates.
The advantage of the butterfly valve is that it has a small volume compared with its diameter and good sealing. The disadvantage is that after the valve is opened, the butterfly plate is still in the center of the circulation pipe, which will cause resistance to the flow of the medium, and the debris in the medium will cause entanglement on the butterfly plate. Therefore, butterfly valves should be avoided in scum pipelines or pipelines with a lot of scum in the medium. In addition, when the butterfly valve is closed. If there is a lot of silt near the butterfly plate, the mud and sand will prevent the butterfly plate from opening again.