Problems with self-priming pumps and centrifugal pumps

The inlet of the centrifugal pump is larger than the outlet. The high flow rate at the inlet shouldn’t be too fast, while a smaller outlet can help maintain the head pressure; I’m not sure if that’s the reasoning

There are many types of centrifugal pumps, among which pipeline pumps have the same diameter at the inlet and outlet. The poster mentioned that the inlet and outlet of a self-priming pump are the same size – there’s no such thing; where did that claim come from?

It’s mainly the pressure difference at the inlet and outlet. . . .

The inlet and outlet of a centrifugal pump can be the same size.

Agreed. A self-priming pump can also have a large inlet and a small outlet, as long as the pump has sufficient self-priming capacity. However, in order to ensure an appropriate self-priming height for such pumps, it’s common to use an intake pipe that is the same size as the pump’s inlet

First of all, self-priming pumps, pipeline pumps, horizontal centrifugal pumps, etc., all belong to centrifugal pumps； Secondly, the inlet diameter of a centrifugal pump is generally larger than that of the outlet pipe, mainly to reduce the resistance at the inlet, which can minimize cavitation ； Once again, the smaller diameter of the outlet pipe is intended to achieve a higher pressure energy (by converting kinetic energy into pressure energy), thereby ensuring an adequate head ； The inlet and outlet diameters of the pipeline pump are equal, mainly to facilitate piping installation ； The inlet of a self-priming pump is not larger than the outlet; it’s the pipe that is narrower, which makes it easier to draw liquid in (the thicker the pipe, the harder it is to draw liquid in, as can be intuitively understood) ； There are also cases where the inlet and outlet of the bedroom centrifugal pump are the same, for example, both are flanged DN25 (it seems that it’s not possible to use a smaller size).

For the self-priming pumps I’ve seen, the diameters of the inlet and outlet pipes are more or less the same

There are too many total types of self-priming pumps, such as ZW, ZX, FZB, ZFB, etc.; the sizes range from large for import use to small for export use.

The inlet diameter of a horizontal centrifugal pump being one size larger than the outlet diameter is intended to address the issue of cavitation in the pump, by reducing the flow velocity of the liquid at the inlet and thereby increasing the cavitation margin. A check valve is installed at the inlet of the self-priming pump; the volume of the inlet chamber is larger than that of the inlet pipeline, and the flow velocity has already decreased, so such a requirement is not necessary.

If the outlet diameter of the centrifugal pump is small, can’t pressure energy be converted into kinetic energy? According to the principle of continuity, a smaller cross-sectional area corresponds to a higher velocity