Abstract: In the transformation of sewage treatment equipment, the valve is re-selected, selected, and maintained to achieve the purpose of safe, reliable and regular use of the valve. Keywords: valve; maintenance; renewal; valve is the main control equipment in sewage treatment plant. Although there are not many types in use, they are large in number and large in size. Most valves are between DN200 and DN700. And most of them are located in underground valve wells, and the space for operation, maintenance, and repair is small. In addition, valve leakage makes the working environment harsh. In the first two years of transformation of the chemical wastewater treatment plant in our plant, the main production facilities built in the 1960s, as well as the main dynamic and static equipment were updated and transformed, but for the special equipment such as valves, due to continuous The characteristics of sex production cannot be fully updated. It is the valves installed and used in that era. The problems that have been exposed until now, such as leakage problems, frequent maintenance, difficult maintenance problems, and the incompatibility of fittings with the current valves on the market have seriously affected the safety and reliability of the valves. Sex, and the quality of sewage treatment. With the increasing awareness of environmental protection and the strict implementation of environmental laws and regulations, the responsibility for environmental pollution caused by valve leakage in the sewage treatment process and the consequences of unqualified sewage treatment caused by the The pressure of influence is also increasing. Therefore, the safety and reliability of the valve, long-term use, especially the prevention of valve leakage, has become a very important issue in the sewage treatment process, and we must attach great importance to it. The following is a discussion on the replacement of valves in the transformation of sewage treatment equipment, and the measures taken in terms of model selection, overhaul and maintenance, especially leakage prevention. 1 The main defects of the original old valve 1.1 The leakage of the valve There are two cases of leakage of the valve, one is internal leakage and the other is external leakage. In sewage treatment, the internal leakage and external leakage of the valve have the same serious harm. Internal leakage causes process fluctuations and unstable water quality. Leakage causes direct environmental pollution, and the leakage of flammable and explosive components contained in industrial sewage forms a dangerous factor, which also makes the valve difficult to repair or replace. Internal leakage analysis: a. Sewage often contains large solid impurities, especially soft materials, such as rubber blocks, plastic blocks, etc., which are squeezed in the middle of the flow channel by the gate, causing the gate to be closed loosely, causing sewage leakage. Because the valves in the main process are mostly parallel double gate valve
s, the thickness of the gate is between 30 and 150mm, so the above situation is very easy to happen. This is the main cause of internal leakage, and the amount of leakage is relatively large. b. The sealing surface of the gate or valve body is corroded and deformed, resulting in a leaky seal. It causes internal leakage of sewage, which becomes continuous discharge of small flow. c. There are quality problems in the manufacturing of the valve, which results in the leakage of sewage due to the imperfect seal of the gate. External leakage analysis: a. The leakage of sewage at the packing is mainly due to improper selection of materials or inconsistent quality; packing is worn and loses elasticity; the diameter of the valve stem becomes smaller when worn; the packing gland is loose and other reasons, which is packing leakage The main form. In the past, the gate valve usually used oil-soaked packing, which is more likely to lose elasticity and be worn after being soaked in sewage and sludge. b. The valve body leaks. Common low-pressure gate valves are usually made of gray cast iron, which is prone to defects such as blisters during casting. The blisters on the valve body will rapidly expand under the erosion of sewage and sludge, and change from leakage to leakage. c. The stem of the low pressure gate valve is made of ordinary carbon steel, which is easily corroded by sewage, so that the diameter becomes smaller, and the sewage will leak through the packing; also because the stem of the ordinary gate valve is not directly connected to the valve plate, but in the middle There is also a movable connection block, so that the valve stem may be stuck in a certain position during the up and down movement, so that the valve can neither be closed nor opened. In this case, the leakage will be large. 1.2 Problems in valve maintenance Another outstanding problem of the original old valve is that the frequency of maintenance is high, the service period is short within 6 months, and the maintenance is difficult. The main reasons are as follows: a. Sludge , There are many solid impurities in the sewage, especially soft blocks such as rubber blocks, which are easy to stay in the valve flow channel and be pressed by the thicker valve plate, making it difficult to close the valve, and the operator is likely to use excessive force, resulting in The valve plate is stretched too far, and the connecting body is stuck in the middle of the valve plate, or even crushed. b. Due to wear, the connecting block is separated from the valve stem or the valve plate, so that the valve stem completely loses command of the valve plate. c. It is difficult to match the original valve accessories with the current valves on the market, and it is difficult to solve the accessories during maintenance. d. Due to the leakage of sewage, the maintenance and repair environment of the valve is harsh, and the underground construction must be erected with a hanger, coupled with special safety protection, which greatly increases the difficulty and cost of the maintenance. e. The management is difficult. Under such harsh environment, it brings great difficulties to the daily inspection, maintenance, and lubrication of the operators, making it difficult to perform these tasks.
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