Dry goods share, one minute to take you to understand the selection principle of the open pump
The parallel adjustment mode of the central pump is that when a single central pump can not meet the transmission task, the central pump can be operated in parallel or in series. Two centrifugal pumps of the same type are parallel, although the pressure head changes little, the total transport flow increases, and the total efficiency of the parallel pump is the same as that of a single pump. When the pump starts in series, the total pressure head increases and the flow rate changes little. The total efficiency of a series of pumps is the same as that of a single pump. After the two pumps are connected in parallel, the flow and pressure head increase, but due to the limitation of the pipeline characteristic curve, the pipeline resistance increases, and the total throughput after the two pumps are connected in parallel is twice that of the original single pump. After the two pumps are connected in series, the pressure head and flow rate will also increase, but the total pressure head after the two pumps are connected in series is still less than twice the original single pump.
The cavitation of the middle open pump is when the pressure P1 at the entrance of the middle pump is equal to or less than the saturated vapor pressure PV of the liquid at the same temperature, the liquid will vaporize. Under the action of high pressure, the bubbles will rapidly coalesce or rupture, resulting in extremely high pressure and frequency of impact. The pump will produce strong vibration and noise, and the liquid flow, pressure head (outlet pressure) and efficiency will be significantly reduced. This phenomenon is called cavitation of open centrifugal pump.
The operation of the middle pump (energy conversion) is that before the pump starts, the pump shell is filled with liquid to be transported; After starting, the impeller is driven by the shaft to rotate at a high speed, and the liquid between the blades must also rotate accordingly. Under the action of centrifugal force, the liquid is thrown from the center of the impeller to the outer edge and obtains energy, and leaves the outer edge of the impeller at high speed and enters the volute pump shell. In the volute, the liquid slows down due to the gradual expansion of the flow path, and then converts part of the kinetic energy into static pressure energy, and finally flows into the discharge pipe at a higher pressure to be sent to the place where it is needed. When the liquid flows from the center of the impeller to the outer edge, the center of the impeller forms a certain vacuum. Since the pressure above the tank level is greater than the pressure at the pump inlet, the liquid is continuously pressed into the impeller. It can be seen that as long as the impeller keeps rotating, the liquid will be continuously inhaled and discharged.
What is the selection principle of the middle pump? Let's take a quick look at it.
Open pump is a widely used general mechanical equipment, it is widely used in petroleum, chemical industry, electricity metallurgy, mining, ship selection, light industry, agriculture, civil and national defense, occupies an important position in the national economy.
The so-called reasonable choice of open pump is to comprehensively consider the pump group and pump station investment, operating costs and other comprehensive technical and economic indicators, so that it is in line with the principles of economy, safety and applicability, specifically, there are the following aspects:
1. It is necessary to meet the requirements of flow and head, that is, the working point of the pump (the intersection of the characteristic curve of the device and the performance curve of the pump) is always maintained in an efficient interval, which saves electricity and is not easy to damage the parts. 2. The selected pump should be small size, light weight, low cost, good performance and high efficiency. 3. Good anti-cavitation performance, stable operation, long service life. 4. The selected pump project has less investment and low operating costs.