Is the centrifugal pump inlet eccentric head installed flat on top or flat on the bottom?

　　On the end suction type centrifugal pump (i.e., the pump inlet for the horizontal inlet) inlet piping on the eccentric size of the head of the installation problem, in the relevant pump piping standards in the textbook, the provisions of its: eccentric reducer diameter orientation on the horizontal pipe (the horizontal part of the upward or downward), according to the non-appearance of the liquid bag or air pocket to decide (divided into two cases):

　　1, when the medium from the top down into the pump, the bottom of the flat eccentric size head installation, no liquid pockets;

　　2, when the medium from the bottom up into the pump, using the top flat eccentric size head installation, there is no airbag.

　　Overview is generally “up into the bottom flat, down into the top flat”.

　　To figure out the reason, first understand a knowledge point: the phenomenon of cavitation, of course, if you just do industrial installation, you do not need to know so much, because in each pump manufacturer's instructions have a complete and correct installation method, just need to follow the construction of the diagram on the line.

　　1.Cavitation phenomenon

　　Centrifugal pump working principle: the driving machine through the pump shaft drives the impeller to rotate to produce centrifugal force, under the action of centrifugal force, the liquid along the vane runner is thrown to the impeller outlet, the liquid is collected by the worm casing and sent to the discharge pipe. Liquid from the impeller to obtain energy, so that the pressure and speed energy are increased, and rely on this energy to transport the liquid to the workplace. In the liquid is thrown to the impeller outlet at the same time, the impeller inlet to the center of the formation of a low-pressure, in the suction tank and the impeller center of the liquid between the pressure difference, the liquid in the suction tank in the role of the pressure difference, and constantly through the suction pipeline and the pump suction chamber into the impeller.

　　According to the working principle of centrifugal pumps can be seen, the liquid flow is in the suction tank pressure Pa and impeller inlet minimum pressure Pk formed between the pressure difference (Pa-Pk) under the action of the impeller, the lower the impeller inlet pressure Pk, the greater the suction capacity. However, if Pk is reduced to a limit value (at present, more to the liquid at the transport temperature of saturated vapor pressure Pt for the critical value of the liquid vaporization pressure), there will be vapor corrosion phenomenon.

　　2. Cavitation will cause serious consequences:

　　(1) produce vibration and noise.

　　(2) have an impact on the performance of the pump: when the development of cavitation to a certain extent, a large number of vapor bubbles, will block the flow channel, so that the pump flow, head, efficiency, etc. are significantly reduced.

　　(3) The material of the runner will have damage: mainly in the vane inlet near the metal fatigue corrosion.

　　3. Improve the centrifugal pump anti-cavitation performance methods are:

　　A. Improve the machine pump structure, reduce Δhr, is a machine pump design issues.

　　B. Improve the effective cavitation margin in the device: the main and most commonly used method is to use the filling head suction device.

　　In addition, minimize the suction line resistance loss, reduce the saturation vapor pressure of the liquid, that is, in the design of the suction line as much as possible to choose a larger diameter, shorter length, fewer elbows and valves, the temperature of the transported liquid as low as possible, and other measures, can improve the device's effective cavitation margin.

　　Well, understand the above knowledge points and then look at the role of the size of the head? Is used to change the size of the pipe diameter. So what is the use of changing the size of the pipe diameter in the import and export of the pump? Mainly to reduce the medium in the pipeline flow rate, reduce the flow rate to reduce the medium in the pipeline flow friction.

　　Centrifugal pump inlet level of the eccentric reducer is generally used in the top flat arrangement, but in the case of the reducer and upward bending elbow direct connection, can be used in the bottom flat arrangement. The reducer should be close to the pump inlet. The reason for top-flat installation is: to prevent the accumulation of gas in the eccentric reducer, and enter the centrifugal pump, cavitation damage to the pump. Horizontal suction centrifugal pump inlet reducer, pipeline from the bottom up into the pump using the top flat installation, from the top down into the pump using the bottom flat installation (in order to prevent the accumulation of gas in the mouth of the pump is also used in the top flat installation), the medium with impurities and suction speed is lower than the speed of impurities settling using the bottom flat installation. The principle is not to form gas pockets.