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The most common problems and avoidance of Roots vacuum pump

Addtime： 2020-07-17 Browse times： 2981

Achieving the most perfect vacuum solution at the most reasonable price is usually the main criterion for decision-making. However, there is a risk that in order to reduce the cost, people may choose a less ideal vacuum solution. This decision will eventually reduce the normal operation time of the customer's equipment and even spend more maintenance costs for it. In the long run, choosing reliable vacuum pump and corresponding accessories, as well as reasonable monitoring and operation mode can bring you more benefits.

It is not uncommon to make many mistakes in the selection and operation of Roots pumps. Errors can be avoided by taking into account only the specific parameters valid for each pump model. In the following, you will see an overview of the most important information about the operation, selection and maintenance of commonly used Roots pumps.

Roots pump - compact structure, high pump speed

Roots pump needs to operate at pure volume level, and compared with rotary vane vacuum pump, roots pump has no internal compression function. It can compress the exhaust pressure. All parts are oil-free in contact with media.

This is why roots pump is called "dry running pump". Its main characteristics are compact structure and high pump speed. Roots pump named after its inventor, namely "roots" brothers.

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 its higher material strength, is more suitable to withstand such heat fluctuations.

3. Temperature control

If the roots pump is operated at 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 the air pumped out by the front stage pump at 100 hPa takes up most of the pumping time. The roots pump can operate effectively only with a minimum pressure of 10 HPA. Therefore, the size of the front stage pump must be correspondingly larger.

5. Turn on the pump

Sudden fluid intrusion can damage the pump as rapid cooling occurs. The gas cannot reach the temperature required to vaporize the liquid. 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. To prevent this, it is necessary to install a receiver between the treatment chamber and roots pump so that the liquid is absorbed before entering the pump.

6. Liquid intrusion

6. 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. A so-called debris net should be installed at the inlet of roots pump. This prevents large solids and weld beads from shooting out of the welded joint due to improper cleaning when the system is first used. In this case, it is recommended to use the pump manufacturer's accessories as the debris protection net is designed to match the nominal diameter of the pump. This ensures that the pump speed will not be affected by unexpected conductance loss.

7. Extraction of critical gas

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. PFA vacuum provides 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. However, the operator must rely on the pump manufacturer for maintenance because this type of enclosed motor is specially developed for the pump. In case of magnetic coupling, a cost-effective standard motor can be used. PFA vacuum provides magnetic coupling up to 250 m3 / h for two-stage rotary vane vacuum pump and 12000 m3 / h for Roots pump.

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