# Basic parameters of centrifugal pumps

Posted by angroup on September 24, 2021

The basic parameters of a centrifugal pump include the pump
Flow rate
Speed
Shaft power
Efficiency
NPSH

## Flow rate

The flow rate of centrifugal pumps is divided into volume flow rate and mass flow rate
Hugh volume flow is the volume of liquid pumped by the pump in a unit of time, that is, the volume of liquid discharged from the pressure outlet section of the pump. Volume flow is expressed in Q, and its unit is cubic meters per hour (m3/h).
Mass flow is the mass of liquid pumped per unit of time, mass flow q, the unit of tons per hour (t / h). Engineering customary use t/h as a unit.
The flow rate of the pump is usually referred to as volume flow, only in rare cases to use the mass flow rate.
The relationship between the volume flow rate of the pump Q mass flow rate q is:

The term head is used instead of pressure in the centrifugal pump business. refers to the energy obtained by the single weight fluid through the pump.

The head of the pump depends on the structure of the pump (such as the diameter of the impeller, the bending of the blades, etc., and the speed. At present, the pressure head of the pump cannot be calculated theoretically. Generally, the experimental method can be used to determine the head of the pump. The experimental measurement is to install a vacuum gauge at the inlet of the pump and a pressure gauge at the outlet. If the kinetic energy difference between the two gauge sections (Δu2/2g=0) is not counted, the energy loss between the two gauge sections (∑f1-2 =0).
Pay attention to the following two points:
(1) where p2 is the reading of the pressure gauge at the outlet of the pump (Pa); p1 is the reading of the vacuum gauge at the inlet of the pump (negative gauge pressure, Pa).
(2) Pay attention to distinguish the two different concepts of centrifugal pump head (pressure head) and lifting height.

## Rotating speed

The speed of the pump refers to the number of revolutions of the pump rotor per unit time. The speed of the pump is represented by n, and its unit is revolutions per minute (r/min) or revolutions per second (r/s).
Rotation speed can also be expressed by the rotational angular speed O of the rotor, its unit is per second (1/s), and the relationship between rotation speed and angular speed is

## Shaft power

The work given to the pump shaft by the prime mover per unit of time is called shaft power, and the shaft transmits the power (motor power) to the power parts (impeller), and the power value is less than the rated power of the motor.

## Efficiency

Pump in the process of transporting liquid, shaft power is greater than the power obtained from the impeller of the liquid discharged to the pipeline, because the volume loss, hydraulic losses mechanical losses are to consume part of the power, and the efficiency of centrifugal pump that reflects the pump to the extent of the use of external energy.
Pump efficiency value and the type of pump, size, structure, manufacturing accuracy, and the nature of the transported liquid related. Large pump efficiency value is higher, small pump efficiency value is lower.

## NPSH

When the pump is working, the liquid will generate the gas at the inlet of the impeller due to certain vacuum pressure. The vaporized bubbles will degrade the impeller and other metal surfaces under the impact movement of the liquid particles, thereby destroying the impeller and other metals. At this time, the vacuum pressure is called vaporization. Pressure, net positive suction head refers to the excess energy that exceeds the vaporization pressure per unit weight of liquid at the suction port of the pump