In wastewater treatment facilities, valves are widely used to control the flow of media or completely intercept the flow of media. There are many types of valves used in water treatment projects, most of which use shaped products. When anti-corrosion requirements are required, chemical valves are used. If there are special requirements, they can be designed and manufactured separately. In terms of the types of media, the valves used in wastewater treatment plants include sewage valves, sludge valves, clean water valves, gas valves, and oil valves. In terms of function, there are globe valves, flow control valves, check valve
s, safety valves, etc. In terms of structure, there are gate valves, butterfly valves, ball valves, plug valves, angle valves and so on. The most basic parameters of the valve are the flow diameter and the working pressure of the medium. The following introduces several commonly used valves in wastewater treatment. 1. Gate valve The flow medium of the gate valve can be clean water, sewage, sludge, scum, oil or gas. Its circulation diameter is generally 50~1000mm, and the maximum working pressure can be larger than 2~4MPa. The characteristic of the gate valve is that the passage is completely barrier-free when the valve is fully opened, so the resistance of the fluid passing through the valve is minimal, and there will be no entanglement, so it is suitable for use in sewage and sludge pipelines containing a lot of impurities. However, gate valves have shortcomings such as long sealing surfaces, easy leakage, and large volume. The gate valve is composed of a valve body, a gate plate (also called a plug-in plate), a seal and an opening and closing device. Because 6-12 shows a single gate valve. The opening and closing method of the gate is reciprocating translation. In order to prevent leakage, the two planes and two sides of the gate must form a good seal with the valve body. Therefore, a long and narrow gap between the valve body and the gate must be inlaid with Bronze, rubber or comb tooth shape. The opening and closing device of the gate valve has open rod and concealed rod, which can be manual, electric or hydraulic. 2. Butterfly valve Butterfly valve is the most widely used valve in wastewater treatment. Its circulating 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 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 directly rotated by the handle. For larger ones, worm gear is used to reduce the force. For those with a diameter greater than 500mm, gear reduction and spiral reduction must be added to reduce The board rotates. The advantage of the butterfly valve is that it has a small volume compared with its diameter and good sealing performance. The disadvantage is that after the valve is opened, the butterfly plate is still horizontal 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 more silt near the butterfly plate, the mud and sand will prevent the butterfly plate from opening again. 3. Ball valve The characteristic of the ball valve is that the valve core is a spherical shape with a through hole with the same diameter in the middle. The opening and closing method of the valve is the same as the butterfly valve-the rotation of the valve core. When the axial position of the through hole is parallel to the direction of medium flow, the valve is fully open; when the position of the through hole is perpendicular to the direction of medium flow, the valve is fully closed. Therefore, there are no obstacles in the pipeline through which the medium flows, and even if there is mud and sand when closed, it will not hinder the reopening. Figure 6-14 is a structure diagram of a small ball valve. The ball valve has good seals, flexible action, and a wide range of media. Some ball valves can withstand a pressure of 20MPa. In sewage treatment plants, ball valves are often used in small and medium-sized pipelines containing more debris, such as sludge and flotation pipelines. In addition, with its characteristics of good sealing and high pressure resistance, ball valves are often used in the biogas pipeline of the sludge digestion system. The opening and closing of the ball valve is rotating, and the form of the opening and closing device is similar to that of the butterfly valve. The disadvantage is that compared with the aforementioned two valves, the volume and mass of the ball valve with the same diameter are much larger, and the cost is also higher. For this reason, ball valves with a diameter greater than 400mm are generally rare. 4. Conical mud valve The conical mud valve is mostly used for sludge discharge at the bottom of a sedimentation tank or aeration tank. On a static pressure suction dredge, the conical mud valve is used to control the flow of living sludge. The opening and closing method of the conical mud valve is up and down translation, the valve plate is connected with the screw, and the open rod screw, electric or manual opening and closing are generally used. The working characteristic of the conical valve is that when the medium degree is 0.2, its flow rate changes the most. The flow rate at 0.2 opening is 80% of that of today, o. When the opening degree is 3, it is the same as the full combination. Most of the poppet valves have a maximum opening degree of 0.3~0.4. The opening of the cone valve refers to the ratio of the lifting height to the diameter. The seal between the valve plate and the valve body of the conical mud valve is inlaid with bronze or rubber. In some parts that do not require high sealing or only need to adjust the flow rate and do not need to be completely closed, the poppet valve without inlay is widely used. For example, the poppet valve on the suction dredge rarely uses the sealed inlay.
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