# Fluid Mechanics – Choosing a centrifugal pump

### ELECTION OF A CENTRIFUGAL PUMP AND ELECTRIC MOTOR DRIVE, TRANSPORT OF A FLUID BY A PRESSURE DUCT.

It is common practice in Engineering and Industrial Maintenance, calculate the characteristics of a centrifugal pump, to drive a fluid through a conduit of known dimensions and nature (length, diameter, absolute roughness).

In the basic analysis of the installation, the Energy Equation gives us the height gauge (J/N=m) (column of fluid meter, specific energy) we need to bring the fluid, for flow (Q = m³ / s), the cargo-passenger.

These two values, we determine the Operating Point, contrast the characteristic curve when the pump; provided by the manufacturer (driving curve), with the characteristic curve of the installation (resistant curve), which grows quadratically with increasing flow.

Multiplying these two parameters for the specific gravity (N / m) obtain the energy flow (J/s) it has to receive the fluid; for transport to the desired conditions of pressure and height.

Three central issues have to enter our target, good choice for pump, and correct operation in the installation:

• First, The operating point should be approximately maximum performance, for the design flow. Check the yield curve / caudal ( n / Q).
• Second, electric motor (usually asynchronous), must actuate the pump shaft, must provide the necessary speed to the design flow and possible changes of regime. For these cases, requires the use of frequency rectifiers (variable speed drives), for optimize energy consumption and further compensate the reactive power required for the engine.
• Thirdly, the pressure at the pump inlet must exceed, with some margin, vapor pressure at the temperature of the fluid transport, to avoid cavitation problems. Basically we limited the suction (hasp), to grow since this; the inlet pressure is reduced significantly. (example; if we transport water, a meter tall, pressure is lower 10 kPa)

Conclusion: Choosing the proper motor-pump for pumping our facility, should first assure us design flow we need, but we must also take into account paragraphs energy optimization, and analyzing the pressures of the vacuum pump inlet, Non produce cavitation conditions.