Generally called the reducer refers to the size of head, reducing the short section for less than DN50 pipeline, in principle, only the use of concentric reducer short section; Reducing pipe hoop for less than DN40 pipe, can not use different diameter short section Reducing the diameter of the hoop can also be used. From the point of view of the use of large diameter reducer because of quality, stress and other issues there may be security risks, in order to ensure the use of safety, so the size of the connection, the import of pumps must be eccentric head, to avoid cavitation, Inside and outside the wire, to the nineties there is no product. For process piping, usually carbon steel forging. In actual use, different diameter hoop has captured the positions of different diameter short section, usually only two, size head and reducer, but also the petrochemical standard can be found in the pipe. Specific details can be found in "SH 3012-2000 Petrochemical Pipe Layout Design General" 5.1.3. Eccentric reducer is mainly installed on the level of the pipe, the top of the flat pipe is to prevent the accumulation of gas in the upper part, usually liquid pipe, the bottom of the flat pipe is to prevent the lower fluid, usually installed in the gas pipeline. Generally liquid tube, the bottom of the flat pipe is to prevent the lower fluid, generally installed in the gas pipeline. The main characteristics of the process to determine the use of concentric reducer or eccentric reducer. The eccentric reducer is mainly installed on the horizontal pipe. If the diameter of the reducer is different from the inner diameter of the process pipe, the corresponding diameter reducer or diameter expansion should be carried out. If the pipe is retracted, this should be considered Will the pressure loss affect the process? In order to prevent the installation of different diameter pipe flow field distribution, resulting in pressure loss, thereby reducing the accuracy of electromagnetic flowmeter measurement, the required center cone angle α is not greater than 15 °, the smaller the better. There are two types of concentric and eccentric, concentric reducer is generally used in the vertical pipe; eccentric reducer for horizontal pipe, and pay attention to indicate the top level or bottom level.