A water pump is a machine that transports liquid or pressurizes liquid. It usually uses a motor or other power equipment to drive the impeller to rotate. After the liquid is sucked from a low place, it is converted into kinetic energy through the impeller to generate pressure, thereby transporting the liquid to a high place or a long distance. The main performance parameters of a water pump are: flow rate, head, power and efficiency.
1. Flow rate of water pump performance parameters The flow rate of a water pump refers to the volume or weight of liquid transported by the water pump per unit time. It is represented by the symbol Q. Common units are m³/h, m³/s, L/s or t/h.
The flow rate marked on the nameplate of the water pump is the design flow rate of the pump, also known as the rated flow rate. The water pump operates most efficiently at the rated flow rate. Instrument Dot-to-Dot Anti-Plagiarism
The water pump flow calculation formula is:
Q=P×η/2.73H
Where: Q is the flow rate, unit m³/h; P is the shaft power, unit KW; η is the water pump efficiency, unit %; 2.73 is a constant; H is the head, unit m.
2. Pump performance parameters of head
Pump head refers to the energy added by the unit gravity of liquid from the pump inlet to the outlet, that is, the energy obtained by the unit gravity of water after passing through the pump. Generally speaking, it refers to the height to which the pump can lift water. It is represented by the symbol H, and its unit is mH2O, which is generally simplified to m. Centrifugal pump head The centrifugal pump head is based on the impeller centerline and consists of two parts. The vertical height from the centerline of the pump impeller to the water surface of the water source, that is, the height to which the pump can suck up water, is called the suction head, or suction head for short; the vertical height from the centerline of the pump impeller to the water surface of the outlet pool, that is, the height to which the pump can press up water, is called the pressure head, or pressure head for short. The centrifugal pump head is equal to the sum of the suction head and the pressure head.
The head marked on the pump nameplate is the design head of the pump, also known as the rated head, which corresponds to the head when passing the design flow. The pump head calculation formula is:
H=(p2-p1)/ρg+(v2²-v1²)/2g+z2-z1
Where: H is the head, unit m; p1, p2 is the pressure of the liquid at the pump inlet and outlet, unit Pa; v1, v2 is the flow rate of the liquid at the pump inlet and outlet, unit m/s; z1, z2 is the inlet and outlet height, unit m; ρ is the liquid density, unit kg/m³; g is the acceleration of gravity, unit m/s².
3. Power of pump performance parameters Pump power refers to the work done by the pump per unit time, usually represented by the symbol N, and the commonly used unit is KW.
Pump power can be further divided into shaft power, effective power and matching power.
The shaft power marked on the pump nameplate refers to the shaft power corresponding to the design flow rate, also known as rated power.
The shaft power refers to the power transmitted to the pump shaft by the power machine (motor), which can be understood as the input power of the pump. Generally speaking, the pump power refers to the shaft power, which is represented by the symbol P.
The effective power refers to the energy obtained from the pump by the liquid flowing through the pump per unit time, also known as the output power of the pump, usually represented by Pu.
The matching power refers to the power of the power machine (motor) matching the pump, and the matching power value is generally marked on the pump nameplate or sample. The pump power calculation formula of the instrument point-to-point anti-plagiarism is:
P=ρ×g×Q×H/1000η
Where: P is the rated power, unit KW; ρ is the liquid density, unit kg/m³; g is the acceleration of gravity, unit m/s²; Q is the flow rate, unit m³/s; H is the head, unit m; η is the pump efficiency, unit %.
4. Efficiency of water pump performance parameters Water pump efficiency refers to the percentage of the effective power of the pump to the shaft power. It is an important technical and economic indicator of the water pump and is represented by the symbol η.
The efficiency marked on the water pump nameplate corresponds to the efficiency when passing the design flow rate, which is the highest efficiency of the water pump.
It is impossible for the shaft power of the water pump to be fully transferred to the output liquid, and there must be a part of energy loss. The energy loss in the water pump can be divided into three parts, namely hydraulic loss, volumetric loss and mechanical loss, and correspondingly there are hydraulic efficiency ηh, volumetric efficiency ηV and mechanical efficiency ηm.
The efficiency η of the water pump is the product of hydraulic efficiency ηh, volumetric efficiency ηV and mechanical efficiency ηm. The higher the efficiency of the water pump, the smaller its energy loss during operation. The pump efficiency calculation formula of the instrument point-to-point anti-plagiarism is:
η = (H × Q) / P × 100%
Among them, η is the pump efficiency, unit %; H is the head, unit m; Q is the flow, unit m³/s; P is the power, unit KW.
01. Hydraulic loss and hydraulic efficiency: When the liquid flows through the suction chamber, impeller, and discharge chamber of the pump, friction loss, local loss, and impact loss are generated.
Friction loss is the loss caused by the friction resistance between the liquid and the wall of the flow-through component. Local loss is the loss caused by the change of velocity and direction of the liquid in the pump. Impact loss is the loss caused by the liquid at the inlet, outlet, and discharge chamber of the blade when the pump is running under non-design conditions. The greater the hydraulic loss, the smaller the pump head. The head without considering the hydraulic loss in the pump is the theoretical head HT, then the ratio of the pump head H to the theoretical head H to the theoretical head HT is called the hydraulic efficiency ηh.
02. Volumetric loss and volumetric efficiency: After the liquid flows through the impeller, a small part of the high-pressure liquid leaks to the inlet of the impeller through the gap in the pump body (such as the leakage reduction ring) and the axial force balancing device (such as the balancing hole), and another part leaks out of the pump body from the shaft seal device, consuming part of the energy, that is, volumetric loss. The larger the leakage q, the smaller the water output Q of the pump. The ratio of the flow rate Q through the outlet of the pump to the flow rate Q+q through the pump inlet is called the volumetric efficiency ηV.
03. Mechanical loss and mechanical efficiency: When the impeller rotates in the liquid, the outer surface of the front and rear covers and the liquid produce friction loss (wheel loss), and when the pump shaft rotates, the shaft and the shaft seal and bearing produce friction loss. Overcoming the friction loss consumes part of the energy, that is, mechanical loss, and the mechanical loss power is represented by Pm. After deducting the mechanical loss from the input power of the pump, the power transmitted to the liquid by the impeller is called hydraulic power, represented by Pw. The ratio of the hydraulic power of the pump to the shaft power is called the mechanical efficiency ηm.
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