The head of a self-priming pump refers to the height of a unit liquid or the energy given to it as the head of the self-priming pump (also called pressure head), the unit: m liquid column. The size of the head of the self-priming centrifugal pump is related to the pump speed, the structure and diameter of the impeller, and the pipeline conditions. The change of head directly changes the flow rate of the self-priming pump.
Self-priming pump head, self-priming pump head classification, self-priming pump head calculation formula
Self-priming pumps generally mark the head as the outlet pressure at the rated flow, and some also mark the cut-off head. The self-priming pump standard of 50 meters means the head of 50 meters at the rated flow rate. If the flow rate is less than the rated flow rate, the outlet pressure of the centrifugal pump should be greater than 50 meters.
Self-priming pump head classification:
Self-priming pump head points: suction head (lower head), discharge head (upper head), total head (actual head/net head) and device head.
Suction head: it is the height from the center of the pump to the lower water surface, also called the lower head;
Water head: it is the height from the center of the pump to the upper water surface, also called the upper head;
Total head: It is the height from the lower water surface to the upper water surface, that is, the sum of the lower head plus the head, and it is also called the actual head or net head;
Device head: It is the total head plus the resistance loss of the entire pipeline and pump system.
Self-priming pump head calculation formula:
The head of the self-priming pump can be measured in the same experiment, that is, a vacuum gauge is installed at the inlet of the pump, and a pressure gauge is installed at the outlet. If the kinetic energy difference between the two gauge sections (ie Δu2/2g=0) is not counted, the section between the two gauges is not counted. The energy loss (ie ∑f1-2=0).
The head of the water pump can be calculated by the following formula
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.
The pump head refers to the energy obtained by the unit weight of the fluid through the pump. List Bernoulli's equations between two sections (including pumps) in a piping system and arrange them to get
In the formula, H is the head, and the lift height only refers to the term Δz.
Example 2-1 is now measuring the head of a self-priming centrifugal pump. When the working fluid is 20℃ clean water and the measured flow rate is 60m^3/h, the pump inlet vacuum gauge reads 0.02Mpa and the outlet pressure gauge reads 0.47Mpa (gauge pressure). The vertical distance between the two gauges is known to be 0.45m. The suction pipe of the pump and the extruder pipe have the same diameter. Try to calculate the pump head.
Solution:
Check the water density of 1.0*10e3kg/m3 at 20℃,
H=0.45m (1Mpa is approximately equal to 100 meters of water column)
P exit=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)/ρg=0.45+(0.47*10e6-(-0.02*10e6))/(10e3*9.8)=50.45m (water column)
