The Most Common Problems With Roots Pumps And Ways To Avoid These Problems

- May 17, 2018-

The Roots pump needs to operate at a pure volume level. Compared with the rotary vane vacuum pump, roots pump has no internal compression function. But it can compress the exhaust pressure. Besides, all parts in contact with the medium are oil-free. The characteristic of roots pump are compact structure and high pump speed.

1. Running under Extreme Pressure

For Roots pumps that operating under maximum differential pressure, it is not recommended to operate directly under extreme pressure before cooling it. Under extreme pressure, because of the too fast revolving speed, the heat cannot be dissipated by the gas or the surface of the housing. And due to the sudden increase of temperature, the air gap between the rotor and the housing is too small, so the pump will stop rotating. In serious cases, it can cause the vacuum pump to fail completely.

2. Improper Temperature Fluctuations

When the roots pump plug is still hot, a sudden and drastic drop of the ambient temperature will make the pump casing shrink, which can stop the pump rotating. Therefore, sudden changes of the ambient temperature must be avoided at all costs. Besides, the operator should not to suddenly open nearby blinds or other doors, especially in winter.

In addition, the free-standing pump should be placed under the eaves or canopies to prevent from rain. In the event of fire, if the pump contact with water directly, the pump casing may explode, especially those casing made of gray cast iron. The ductile cast iron pump is more suitable to withstand such thermal fluctuations due to the higher strength of the material.

3. Temperature Control

If the roots pump operates under the maximum differential pressure, a temperature sensor need to be installed at the discharge end to prevent overheating and any resulting damage. The temperature sensor will alarm at a defined temperature and turn off the pump when it reaches the maximum allowable temperature.

4. Fast Evacuation

In the application, a few seconds of extraction cycle must be realized, so the operator must ensure that the ratio of the roots pump to the backing pump is 1:2. It is necessary to keep this ratio because the backing pump makes air be pumped out at a pressure of 100 hPa, which occupies the most of pumping times. While the roots pump can operate efficiently only from a pressure of 10 hPa. Therefore, we believe that the size of the backing pump should be correspondingly larger.

5. Start the Pump

If a multi-stage pumping station or multiple parallel-operated vacuum pump combinations are used, it is necessary to start these pumps at staggered intervals. The first is atmospheric pump, which avoids excessive power peaks to protect high-cost breaker. This method can be easily implemented by controllers and PLCs with timing elements. Another method is to start the pump slowly by a frequency converter.

6. Liquid Intrusion

Sudden liquid intrusion can damage the pump, because he gas cannot reach the desired temperature to evaporate the liquid when a sudden cooling occurs. The extra steam cannot be pumped out in time because the backing pump is already overloaded and the backing pressure may rise to an excessive level. So it is necessary to install a receiver between the chamber and the roots pump to ensure the liquid is absorbed before entering the pump.

7. Dust Accumulation

In processes that may generate particles or carry dust, such as metallurgy or crystal pulling, it is necessary to install a dust filter at the inlet of the pump to protect the roots pump and the downstream pump. Besides, a so-called debris protection net should be installed at the inlet of the roots pump to prevent the larger solids and beads from the welded joint due to improper cleaning at the first time to use. In this case, it is recommended to use the accessories from pump manufacturer because the debris protection net is designed so that its free section corresponds to the nominal diameter of the pump.

8. Pump Rare Precious Gas

When pumping precious and high-purity gases, such as helium-3 or helium-4, these gases must be avoided contacting with ambient air. At this time, the pump body is required to have higher air tightness and lower leakage rate in a region lower than 10-5 to 10-8 hPa l/s. Some vacuum pump manufacturers can provide permanent magnet couplings for motors instead of ordinary shaft feeds, which made leakage on all shaft seals a history.