# Six Steps for the Selecting of Laboratory Vacuum Pumps

The function of the laboratory vacuum pump is to remove gas molecule from the vacuum room through reducing the vacuum room pressure to reach the required vacuum degree. Different vacuum system configurations should be selected to meet different process indexes, working efficiency, equipment working life requirements and different vacuum sections. In order to achieve the optimal configuration of laboratory vacuum pump selection, the following six steps should be given consideration to:

## 1. Determine the type of gas to be pumped and its amount.

Check and determine the type and volume of extraction required by the process.

The laboratory vacuum pump system will be contaminated if the type of gas being pumped reacts with the liquid in the laboratory vacuum pump. Meanwhile, it is also necessary to determine the appropriate exhaust time and the amount of gas produced during the extraction process.

## 2. Determine the vacuum degree.

The degree of vacuum is determined by the structure of the laboratory vacuum pump, and the vacuum is measured by the gauge pressure and absolute pressure. The absolute pressure indicates that the reading is absolute value the closer the reading is to 0 the higher the vacuum is. However, the closer the gauge pressure is to 760 mmHg, the higher the vacuum. This means that if the required absolute pressure (extreme vacuum) is close to zero then only a vacuum pump can meet this requirement, but if the demand is close to 1 bar (ie atmospheric pressure) then a roots blower or a centrifugal blower can be used.

## 3. Determine the operating vacuum range.

Because each process has its own vacuum range. Laboratory vacuum pump selection is checked to determine the vacuum required for each process.

## 4. Determine the vacuum volume for inspection.

Determine the time required to achieve the required vacuum, flow resistance and leakage of the vacuum piping. Consider the pumping rate required to maintain the vacuum under certain process requirements after achieving the required vacuum.

## 5. Determine the ultimate vacuum.

The ultimate vacuum of the vacuum pump system is checked on the basis of determining the degree of vacuum required by the process, since the ultimate vacuum of the system determines the optimum working vacuum of the system. Generally speaking, the ultimate vacuum of the system is 20% lower than the working vacuum of the system and 50% lower than the ultimate vacuum of the foreline pump.

## 6.Vacuum pump calculation formula.

S=2.303V/tLog(P1/P2). S refers to the vacuum pumping rate (L/s), V refers to the vacuum chamber volume (L), t refers to the time required to reach the required vacuum (s), and P1 refers to the initial vacuum. Degree (Torr), P2 refers to the required vacuum (Torr).

The above formula is only a theoretical calculation result and a number of variable factors are not taken into account, such as pipe flow resistance, leakage, flow resistance of the filter, temperature of the pumped gas, safe absorption, and the like.