Addtime： 2020-07-18 Browse times： 3019
Dry vacuum pump needs to operate at pure volume level, and roots pump has no internal compression function compared with rotary vane vacuum pump. It can compress the exhaust pressure. Compared with rotary vane vacuum pump, all parts in contact with medium are oil-free, and all parts suitable for Roots pump are also suitable for dry vacuum pump. It is characterized by compact structure and high pump speed. How to avoid the most common problems when using dry vacuum pump?
1. Operating at extreme pressure
For Roots pump operating under maximum differential pressure, it is not recommended to operate directly under the limit pressure before cooling it. At the limit pressure, due to the vacuum pump speed is too fast, the minimum or zero gas through the gas or shell surface will not emit any heat. Due to a sudden increase in temperature, the air gap between the rotor and the casing is too small, and the pump will stop rotating. In severe cases, this can lead to complete failure of the vacuum pump.
2. Improper temperature fluctuations
When roots pump plug is still very hot, a sudden sharp drop in ambient temperature will cause the pump casing to shrink and cause the pump to stop rotating. As shown in Figure 1, this is particularly important when working at extreme pressure. Therefore, it is necessary to avoid abrupt changes in ambient temperature at all costs. In addition, the operator must pay attention not to suddenly open the nearby blinds, other doors, etc., especially in winter.
In addition, for those self-supporting pumps, to put it in the eaves or canopy, so as not to be rain. If water is directed directly at the pump in case of fire, the pump casing may explode, especially those made of gray cast iron. Nodular cast iron version of the pump, due to the higher strength of its material, more suitable to withstand such heat fluctuations.
3. Temperature control
If the roots pump is operated at its maximum differential pressure, a temperature sensor needs to be installed at the exhaust end to prevent overheating and any damage resulting from it. This will generate an alarm at a limited temperature and will shut down the pump when it reaches the maximum allowable temperature.
4. Quick evacuation
In the application, it is necessary to realize the extraction cycle of several seconds, so the operator must ensure that the ratio of roots pump and front stage pump is 1:2. It is necessary to ensure this ratio, because most of the pumping time is taken up by the front stage pump to pump out the air at 100 hPa, while the roots pump can operate effectively only at the pressure of 10 HPA. Therefore, the size of the front stage pump must be correspondingly larger.
5. Start the pump
If a multi-stage pumping station or a combination of vacuum pumps operating in parallel is used, it is necessary to start these pumps at staggered intervals, starting first with the atmospheric pump, so as to avoid excessive power peaks and protect high-cost circuit breakers. This can be easily realized in the controller and PLC by timing element. Another way is to use a frequency converter to start the pump slowly.
6. Liquid intrusion
Sudden liquid intrusion can damage the pump because the gas cannot reach the required temperature to vaporize the liquid in the event of a sharp cooling. The extra steam cannot be pumped out in time because the front stage pump is overloaded and the pressure of the front stage may rise to an excessively high level. In order to prevent this, it is necessary to install a receiver between the treatment room and roots pump so that the liquid is absorbed before entering the pump.
7. Dust accumulation
It is necessary to install a dust filter at the air inlet of the pump to protect roots pump and downstream pump in the process of producing particles or carrying dust, such as in metallurgy or crystallization process. The so-called debris protection net should be installed at the air inlet of roots pump to prevent large solid substances and welding beads from shooting out of the welded joint due to improper cleaning when the system is used for the first time. In this case, it is recommended that the pump manufacturer's accessories be used as the debris protection net is designed to match the free section with the nominal diameter of the pump.
8. Extraction of rare and precious gases
When extracting valuable and highly pure gases, such as helium 3 or helium 4, contact with the surrounding air must be avoided at all costs. At this time, the pump body is required to have high air tightness and low leakage rate in the area less than 10-5 to 10-8 HPA L / s. Some vacuum pump manufacturers, such as PFA vacuum, can provide permanent magnet coupling for motor instead of common shaft feed through parts. This makes the leakage on all shaft seal rings history. Enclosed motors can also be used, but the operator must rely on the pump manufacturer for maintenance, as this type of enclosed motor is specially developed for the pump. For example, with magnetic coupling technology, a cost-effective standard motor can be used.
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