The head of water pump is the lift of unit liquid or the energy given is called pump head (also called pressure head), unit is meter (liquid column). The head of centrifugal water pump is related to the speed of pump, the structure and diameter of impeller, and the condition of pipeline. The change of the head directly changes the flow of the pump.
The pump lift is divided into four parts: suction head (lower head), outlet head (upper head), total head (actual head / net head) and device head.
Suction head: the height from the pump center to the lower water surface, also known as the lower head;
Discharge head: the height from the center of the water pump to the upper water surface, also known as the upper head;
Total head: the height from the lower water surface to the upper water surface, that is, the sum of the lower head and the head, also known as the actual head or net head;
Head of device: it is the total head plus the resistance loss of the whole pipeline and water pump system.
The head of the water pump can be determined by experiment, that is, a vacuum gauge is installed at the pump inlet and a pressure gauge is installed at the outlet. If the kinetic energy difference (Δ U2 / 2G = 0) and the energy loss (Σ f1-2 = 0) between the two surface sections are ignored.
Then the head of water pump can be calculated by the following formula:
H = H + (P2 - P1 ) / ρg
Note the following two points:
1. Where P2 is the reading of the pressure gauge at the pump outlet (PA); P1 is the reading of the vacuum gauge at the pump inlet (negative gauge pressure, PA).
2. Pay attention to the two different concepts of head (head) and lift height of separation core pump.
Pump head refers to the energy obtained by unit weight fluid through the pump. In a pipeline system, Bernoulli equation is listed between two sections (including pump) and it can be obtained
Example 2-1 the head of a centrifugal pump is measured. When the working medium is 20 ℃ clean water and the measured flow is 60m ^ 3 / h, the reading of the vacuum gauge at the inlet of the pump is 0.02MPa, and the reading of the pressure gauge at the outlet is 0.47mpa (gauge pressure). It is known that the vertical distance between the two gauges is 0.45M. If the diameter of the suction pipe and the discharge pipe of the pump is the same, try to calculate the lift of the pump.
Check out that the water density at 20 ℃ is 1.0 * 10e3kg / m3,
H = 0.45M (1MPa is equal to 100m water column)
P outlet = 0.47mpa (0.47 * 100m water column = 47m water column)
P inlet = -0.02mpa (0.02 * 100m water column = 2m water column)
ρ is the density of the liquid
H = H + (P outlet - P inlet) / ρ g = 0.45 + (0.47 * 10e6 - (- 0.02 * 10e6)) / (10e3 * 9.8) = 50.45m (water column)