Roots vacuum unit selection notes

To form a roots vacuum unit, the selection of the pumping speed ratio between the roots vacuum pump and the backing pump is very important.

Because the compression ratio of the Roots vacuum pump is very limited. This compression ratio determines the capacity of the backing pump, because the compression ratio is the inverse ratio of the two pumping speeds. Generally, the compression ratio is selected within 2~10. In addition, consideration should be given to the requirements for pre-sampling time.

Vacuum equipment is used as an auxiliary equipment in various mechanical equipment. If the normal working time is much longer than the pre pumping time, a smaller front stage pump (compression ratio can be larger) can be selected, if the vacuum is larger. Moreover, it is required to pre pump quickly, and a larger front-stage pump is used.

Sometimes, in order to give full play to the efficiency of the equipment, a large pre pumping pump is installed in front of the unit. After normal operation, it is stopped and maintained by a smaller front stage pump. This is to save power.

The requirement of limit pressure of Roots vacuum pump unit must be considered when selecting the front stage pump. The requirement for limit vacuum degree is high (up to 1 × 10-3pa ~ 1 × 10-2Pa) and double-stage rotary vane oil seal mechanical pump or double-stage sliding vane mechanical pump are generally selected as the front stage pump.

When the limit vacuum degree is between 1 × 10-2 PA and 1 × 10-1 PA, the single-stage oil sealed mechanical pump can be selected as the front stage pump, and the reciprocating vacuum pump or liquid ring vacuum pump can be selected as the front stage pump when the limit vacuum degree is between 133 and 1333 PA.

In order to obtain high pumping rate at low inlet pressure (1-100pa), a Roots vacuum pump can be used as a three-stage or four-stage unit composed of another roots vacuum pump. At this time, the pumping speed ratio of Roots vacuum pump is generally between 2 and 5.

Correct combination of roots water ring vacuum unit. Because roots water ring vacuum unit has selective air extraction, sometimes one kind of pump can not meet the requirements of air extraction, and several pumps need to be combined to supplement each other to meet the requirements of air extraction. For example, the titanium sublimation pump has a high pumping speed for hydrogen, but can not pump helium, while the tripolar sputtering ion pump has a certain pumping speed for argon, the combination of the two will make the vacuum device get better vacuum degree. In addition, some roots water ring vacuum units can not work under atmospheric pressure and need pre vacuum; some roots water ring vacuum units have outlet pressure lower than atmospheric pressure and need front stage pump, so they all need to be combined.

Precautions when using vacuum pump unit:

Between the distillation system and the vacuum pump unit, attention must be paid to the installation of absorption device; before distillation, the vapor of organic solvent in the system must be completely pumped out by water pump; if the air can be pumped by water pump, the water pump should be used as far as possible. If the distilled substances contain volatile substances, the water pump can be used to reduce the pressure first, and then the oil pump can be used.

When the vacuum pump unit is in use, the constant change of the cavity volume will directly form the exhaust effect, requiring that the lubricating oil should have the appropriate viscosity and viscosity temperature characteristics; the pressure reducing system on the vacuum pump unit must pay attention to keep tight without air leakage, all rubber stoppers and holes should be appropriate, and the rubber pipe should use the rubber pipe for vacuum. The ground glass is coated with vacuum grease.

The above contents are summarized by EVP vacuum pump manufacturer, and some contents are introduced in detail. If you have requirements in this respect, please contact us.