How to select a multistage pump
It is unlikely that you can buy a centrifugal multistage pump off the shelf, install it in an existing system and expect it to deliver exactly the flow rate you require. The flow rate that you obtain depends on the physical characteristics of your system such as friction which depends on the length and size of the pipes and elevation difference which depends on the building and location. The pump manufacturer has no means of knowing what these constraints will be. This is why buying a centrifugal pump is more complicated than buying a positive displacement pump which will provide its rated flow no matter what system you install it in.
The main factors that affect the flow rate of a centrifugal pump are:
- friction, which depends on the length of pipe and the diameter
- static head, which depends on the difference of the pipe end discharge height vs. the suction tank fluid surface height
- fluid viscosity, if the fluid is different than water.
The steps to follow to select a centrifugal pump are:
.1. Determine the flow rate
.To size and select a centrifugal pump, first determine the flow rate. If you are a home owner, find out which of your uses for water is the biggest consumer. In many cases, this will be the bathtub which requires approximately 10 gpm (0.6 L/s). In an industrial setting, the flow rate will often depend on the production level of the plant. Selecting the right flow rate may be as simple as determining that it takes 100 gpm (6.3 L/s) to fill a tank in a reasonable amount of time or the flow rate may depend on the interaction between processes.
.2. Determine the static head
.This a matter of taking measurements of the height between the suction tank fluid surface and the discharge pipe end height or the discharge tank fluid surface elevation.
.3. Determine the friction head
.The friction head depends on the flow rate, the pipe size and the pipe length. This is calculated from the values in the tables presented here (see Table 2). For fluids different than water the viscosity will be an important factor and Table 1 is not applicable.
.4. Calculate the total head
.The total head is the sum of the static head (remember that the static head can be positive or negative) and the friction head.
2. 5. Select the pump You can select the pump based on the pump manufacturer's catalogue information using the total head and flow required as well as suitability to the application.

Rovatti electrical pumps home page <> About us/Profile<> About us/A partner in problem solving Products/Green Line <> Products/Orange Line <> Technical Info <> Find Us <> Contact us/Information <> Contact us/Job area <> News <> Italian version