Addtime： 2020-07-18 Browse times： 2759
With the rapid development of instrument industry, small size, oil-free and environment-friendly micro vacuum pump and micro diaphragm vacuum pump have been widely used. How to choose the most appropriate product among the various specifications of micro pump?
First of all, the purpose of micro pump should be clarified.
1、 If only use the micro air pump to output compressed air.
In short, it is only used to pump and inflate, and the pump's air outlet is basically not used. This situation is relatively simple, according to the output pressure from large to small can be selected: pcf5015n, faa8006, faa6003, faa4002, fm2002, fm1001. Of course, we also need to refer to the flow index and other relevant technical parameters.
2、 Phw600b or WAA series products should be selected for the following situations.
1. The micro pump is used to pump air or vacuum, but sometimes liquid water will enter the pump chamber.
2. The micro pump is required to be able to pump as well as air.
3. It mainly uses micro pump to pump water, but does not want to rely on manual "water diversion" before pumping. (some pumps need to add some "water diversion" manually before operation, so that the pump can pump water from the lower part, otherwise the pump can not pump water or even be damaged.) The advantage of phw600b or WAA series products is that when there is no contact with water, it will vacuum. After forming a vacuum, the water pressure will be raised by air pressure, and then the water will be pumped.
4. Pump water with a micro pump, but sometimes there may be no water to pump, in the "dry" state. Some traditional pumps are afraid of "dry running", even fatal. However, phw600b or WAA series products are essentially a kind of composite function pump, which integrates the functions of vacuum pump and water pump. Some people call it "vacuum pump". Therefore, in the absence of water, it will vacuum, when there is water, it will pump. Both the pumping state and the pumping state belong to the normal working category, so there is no so-called "dry turning" damage.
3、 If the micro pump is used to pump air, the situation is a little more complicated.
1. Judging the working condition of the pumping end of micro pump
There are two kinds of micropumps for pumping: gas sampling pump and micro vacuum pump. Although they are generally referred to as micro vacuum pumps without distinction, they are different from each other from the technical point of view, so special attention should be paid to the type selection.
In short, the gas sampling pump can only carry a small load (i.e., the resistance at the pumping end of the pump cannot be too large), but the price is cheap; strictly speaking, the micro vacuum pump can carry a large load (large resistance is allowed at the suction end, or even completely blocked), but the price is slightly higher. The specific differences between the two can be seen in the article "the difference between micro vacuum pump and gas sampling pump".
Gas sampling pumps include: PM series (specific models: pm950.2, pm850.5, pm8001, pm7002, pm6503); micro vacuum pumps include: VM series, VAA series, PK series, PC series, VCA series, VCC series, VCH series, pH series, FM series, FAA series, PCF series. All specifications under these series are real micro vacuum pumps, such as vm7002, vaa6005, pc3025, etc.
The resistance at the suction end of the micro pump can be measured by instrument. Comparing it with the por value of the pump's technical parameter "the maximum allowable resistance at the inlet", we can know whether the type selection is appropriate or not. It is usually determined by simple methods according to experience. For example, the following cases are all of high load (i.e. the resistance of the pump suction end is large), so the selection can only be carried out within the scope of micro vacuum pump: ① long pipeline should be connected at the pumping end of the pump, or there are many bending points, severe bending, or even blocking and sealing, or the inner hole of the pipe is very small (such as less than φ 2mm); ② there are some problems in the pipeline Throttle valve, solenoid valve, gas circuit switch, filter and other components; ③ the pump suction port is connected with a closed container, or the container is not sealed but the air intake is small; ④ the pump suction port is connected with the suction cup, which is used to adsorb objects (such as integrated blocks, precision workpieces, etc.); ⑤ the suction end of the pump is connected with the filter container, and the filter screen is placed at the container port to accelerate the liquid filtration.
2. Judging the working condition of the discharge end of micro pump
All of the above are discussing the problem of the suction end resistance of the micro pump. According to these judgment conditions, the selection range has been reduced, but the exhaust end resistance must be considered, so as to finally determine the optional range.
In practical application, the micro vacuum pump is faced with different exhaust conditions: one is that the exhaust is very smooth and straight to the atmosphere; the other is that the exhaust resistance is large, such as valves, small elbows, large damping sensors, non dedicated silencers, exhaust below the liquid level, and gas is discharged to closed or semi closed containers. In modern design and manufacture, micro vacuum pumps with different exhaust conditions are treated differently. The parameter "allowable maximum resistance por value at the exhaust port" is to calibrate the discharge capacity of the pump, so that we can determine whether the selection is appropriate by strict technical means.
In short, for the system with high exhaust resistance, our selection range is: FM series, FAA series, PCF series; for the system with small exhaust resistance, the selection range is: VM series, VAA series, PK series, PC series, VCA series, VCC series, VCH series, pH series. According to the above steps, we have been able to determine the scope of micro pump selection. In the delimited several optional series, we can determine the specific model according to our requirements for flow rate and vacuum degree. For the poor quality products not listed in this paper, try not to use. Attention should be paid to the selection of parameters, especially the flow parameters. When the pump is connected to the gas system, the flow rate will be reduced due to the pressure loss caused by the pipeline, valve and other gas path components, so the flow rate obtained is less than the nominal flow rate of the pump.
There are also some problems related to the type selection listed below, according to the use of consideration.
1. Start with load problem.
If there is vacuum in the suction port or pressure in the exhaust port before the micro air pump is started, another technical parameter of the pump should be considered: the maximum starting load PIs value at the inlet port and the maximum starting load POS value at the exhaust port. A typical application example is to use a micro air pump to maintain the vacuum or positive pressure in the container. When the vacuum or positive pressure in the container is lower than the set value, the pump needs to be powered on to start, and when it is higher than the set value, it will stop. The products that can be started under the limit vacuum degree they can reach are: VM series, VAA series, PK series, PC series, VCA series, VCC series, VCH series and pH series; the products that can be started under the maximum output pressure they can reach are FM series, FAA series and PCF series. This performance requires high technical level of the manufacturer.
2. The medium temperature of micro pump.
According to the temperature of the medium gas through the pump, choose to ordinary type or high temperature type.
3. The reliability of micropump.
According to the micro pump failure after the severity of the consequences, completely according to their own requirements. The average fault free continuous operation time of high-quality products is more than 1000 hours, some as high as thousands of hours. In particular, this parameter is measured under full load and uninterrupted operation, which is the worst working condition. If the actual use is not full load or continuous operation, the value will be higher, and the higher value depends on the working condition of the pump. This performance is a test of the manufacturer's technical strength. It can be seen from the appearance of the products, such as the use of special motors instead of ordinary low-cost motors, and the weight is heavier when the volume is the same. According to the price of the product, we can know a little about it.
4. Electromagnetic interference of micropump.
If there is a precision circuit controlled micropump, depending on the anti-interference ability of the circuit, it may be necessary to order a micro pump with low electromagnetic interference.
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