5. The basic parameters of the pump
The basic parameters that characterize the main performance of the pump are as follows:
1. Flow Q
Flow rate is the amount of liquid (volume or mass) delivered by the pump in a unit of time.
The volume flow is represented by Q, and the unit is: m3/s, m3/h, l/s, etc.
The mass flow rate is expressed in Qm and the unit is: t/h, kg/s, etc.
The relationship between mass flow and volume flow is:
Qm = ρQ
The density of the liquid in the formula (kg/m3, t/m3), normal temperature clean water ρ = 1000kg/ m3.
2. Head H
The head is the increase in the energy of the unit weight of the pumped liquid from the pump inlet (pump inlet flange) to the pump outlet (pump outlet flange). That is, the effective energy obtained by the Newtonian liquid through the pump. The unit is N ● m / N = m, that is, the height of the liquid column pumped by the pump, which is commonly referred to as meters.
3. Speed n
Speed is the number of revolutions of the pump shaft per unit time, represented by the symbol n, and the unit is r / min.
4. Cavitation allowance NPSH
The cavitation surplus is also called the net positive suction head, which is the main parameter indicating the cavitation performance. The cavitation surplus was once expressed by Oh in China.
5. Power and efficiency
The power of the pump usually refers to the input power, that is, the power on the shaft of the transfer pump of the prime mover, so it is also called the shaft power and is represented by P; the effective power of the pump is also called the output power and is represented by Pe. It is the effective energy obtained in the pump from the liquid delivered from the pump per unit time.
Because the head refers to the effective energy obtained from the pump per unit of heavy liquid output by the pump, the product of the head and the mass flow rate and the acceleration of gravity is the effective energy obtained from the liquid output from the pump per unit time-that is, the pump's Effective power:
Pe = ρgQH (W) = γ QH (W)
In the formula
ρ- density of liquid transported by pump (kg / m3);
γ—The gravity of the liquid delivered by the pump (N / m3);
Q—Flow of pump (m3 / s);
H- pump head (m);
g- acceleration of gravity (m / s2).
The difference between the shaft power P and the effective power Pe is the power loss in the pump, and its magnitude is measured by the efficiency of the pump. The efficiency of the pump is the ratio of effective power to shaft power, expressed by η.
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