2.What is Main Performance Parameters of Pumps？
Flow Rate and Head
The amount of fluid pumped by a pump in a unit of time is called the flow rate, which is typically denoted by the symbol Q for centrifugal pumps. The increase in the energy of the liquid under the action of gravity, obtained by the pump, is called the head and can be represented by the symbol H, with the unit being meters (m).
When selecting a water pump, the flow rate and head are the main parameters provided by the design engineers based on the process calculations. These are fixed values. However, in terms of the pump's own performance, the flow rate and head often have a corresponding relationship within a range. These two parameters will influence each other during pump selection. The ideal selection is when the fixed industrial parameters fall within the high-efficiency range of the pump's performance curve. If there are deviations, a comprehensive evaluation of the adverse impacts of the deviations is needed, and the selection result is decided after weighing the pros and cons.
Shaft Power and Efficiency
The power transmitted by the prime mover to the pump shaft is called the shaft power, which can be represented by the symbol P, with the unit being kilowatts (kW). The power obtained from the fluid by the energy-efficient pump in a unit of time is called the effective power, which can be represented by the symbol Pe.
The efficiency of an energy-efficient pump is related to the pump's design level and the level of mechanical processing. The high or low efficiency will directly affect the energy consumption of the pump. Each pump has its own high-efficiency range, and the pump selection should always fall within this high-efficiency range to reduce energy consumption.
Rotational Speed
The rotational speed of the pump shaft, expressed in revolutions per minute (r/min), is denoted by the symbol N. The rotational speed is usually corresponding to the standard speed of the motor, and can be adjusted to achieve higher energy savings using a variable frequency drive.
Cavitation and Net Positive Suction Head
Cavitation refers to the phenomenon where the local pressure in the pump drops below the vapor pressure of the liquid, causing the liquid to vaporize and form a gas-liquid flow. When this gas-liquid mixture reaches the high-pressure region, the bubbles are compressed and collapsed, resulting in high water hammer pressures that can cause erosion and damage to the pump materials. Cavitation is directly related to the pump's performance and the design of the suction system.
Operating Conditions
The physical and chemical properties of the pumped medium, such as characteristics, particle size, particle content, viscosity, density, and vapor pressure, directly affect the pump's structure, materials, and performance.
Site Conditions
The environmental factors, such as ambient temperature, installation location, atmospheric pressure, relative humidity, atmospheric corrosion, and hazardous area classification, also need to be considered when selecting a pump.
