# How to choose a vacuum pump?

How to choose the right vacuum pump? There are many kinds of vacuum pumps, not any one is suitable for you. Maybe according to your factory environment need oil-free dry vacuum pump, maybe the gas is corrosive, need corrosion-resistant vacuum pump; There is also the possibility that a vacuum pump can not meet your requirements, need a number of combination together to meet. What do we need to know before choosing a vacuum pump?

1. Absolute pressure and relative pressure
Vacuum pump absolute pressure refers to the absolute pressure, that is, the real vacuum pressure produced by the vacuum pump. Absolute vacuum is absolute vacuum pressure. Absolute pressure = local atmospheric pressure + surface pressure (relative pressure), the smaller the absolute pressure is, the closer to vacuum!
Ultimate vacuum means that no matter (including molecules, atoms, etc.) exists in this state, which is only a theoretical state and impossible to achieve in practice. It is an important parameter of the vacuum pump, is the characteristic value of the pumping capacity of the reaction pump, is a value related to the vacuum pump, different vacuum pumps can have different limit vacuum; He is a concept of theoretical research, is the exclusion of various practical factors and the extraction of an ideal vacuum state.

2, vacuum pump pumping rate
3. Vacuum degree
Vacuum refers to the degree of gas rarefaction in a vacuum. If the pressure in the device is lower than the atmospheric pressure, the pressure measurement needs a vacuum meter. The value read from the vacuum meter is called the vacuum degree. Vacuum value is the value indicating that the actual pressure of the system is lower than the atmospheric pressure, that is: vacuum = absolute pressure – atmospheric pressure, absolute pressure = atmospheric pressure + surface pressure (vacuum).

### One, the choice of the main vacuum pump seven principles

1. Select the main vacuum pump according to the vacuum pressure required by the factory;

2. Determine the type and model of the main vacuum pump according to the ultimate pressure;

3, according to the vacuum volume size and pumping rate to choose the main vacuum pump;

4, the correct combination of vacuum pump;

5, according to the requirements of the factory production environment to determine the oil vacuum pump or no oil vacuum pump;

6. Select the vacuum pump according to the composition characteristics of the pumped gas;

7, according to the factory vacuum system cost budget and daily maintenance costs, such as the choice of economic and affordable vacuum pump of good quality

### Ii. How to choose the vacuum front-stage pump and the pre-pumping pump

1, according to the main vacuum pump exhaust gas flow to choose;
2, according to the main vacuum pump exhaust maximum pressure to choose;
3, according to the customer required speed and vacuum to choose.

### Vacuum pump selection – why do you need to add a maintenance pump sometimes

In order to prevent the valve pipeline and other leakage and material surface gas caused by reflux, oil vapor oxidation and so on, it is necessary to continue before the pump pump pump exhaust gas or set up to maintain pump exhaust.

## Vacuum pump selection matters needing attention

When choosing a vacuum pump, first of all should pay attention to the selection of the most important requirements of the vacuum pump, the most attention to the performance is what, after the pump to meet this point to consider some other selection requirements. In general, the following should be noted in the selection:

1. The working pressure of the vacuum pump shall meet the requirements of the extreme vacuum and working pressure of the vacuum equipment. For example: vacuum coating requirements 1 x 10-5 mBar vacuum, the selected vacuum pump vacuum limit should be no more than 5 x 10-6 mBar. Usually the choice of vacuum pump vacuum than vacuum equipment vacuum half to an order of magnitude.

2, the correct choice of vacuum pump vacuum degree. Each pump has a certain range of working pressure, such as: the ultimate vacuum is 0.1mBar, its stable working pressure range of 1.0 mBar to 0.5 mBar, therefore, the pump operating point should be selected in this range.

3, the vacuum pump in its working pressure, should be able to drain all the gas produced in the process of vacuum equipment within the specified time, this requires to consider the vacuum pump with load in a certain extent under the premise of the extraction rate.

4, according to the pumping medium to the different, selective selection of vacuum pump. If a pump can not meet the requirements of pumping into the air, but also consider a variety of pump combinations. For example, the pumping rate curve of svf-e1-20 is different when pumping oil-free air and helium, so the characteristics of the pumped medium should be fully considered when considering the vacuum pump.

5, to understand the composition of the gas, the gas contains condensable steam, no particle dust, corrosion, toxicity, etc. When selecting a vacuum pump, it is necessary to know the composition of the pumped gas and select the corresponding pump for the pumped gas. If there is a corrosive gas, then the pump cavity material should choose anti-corrosion materials; If it is toxic gas, vacuum pump also need to consider the leakage rate, in order to avoid toxic gas leakage caused by industrial accidents. Containing condensable steam, particles, and corrosive gases, it is also possible to consider installing auxiliary equipment, such as condenser, dust remover, etc. on the inlet pipe of the pump.

6. Requirements for oil pollution of vacuum equipment. If the equipment strictly requires no oil, should choose a variety of no oil pump, such as: water ring pump, no oil vortex pump, no oil screw pump, etc., if the equipment has strict requirements for water vapor, dust, etc., it is necessary to choose no oil dry pump, such as vortex dry pump, screw dry pump, molecular pump. If the requirements are not strict, you can choose a pump, plus some anti-oil pollution measures, such as cold trap, baffle, oil trap, etc., can also meet the requirements of clean vacuum.

7, the impact of vacuum pump on the environment. Environment does not allow any oil pollution, can choose oil-free vacuum pump; The environment is not allowed to have dust pollution, can choose no debris produced by the pump, such as floating vortex pump, oil-free diaphragm pump; The environment does not allow noise pollution, can choose silent pump.

8. Whether the vibration generated during the operation of the vacuum pump has any influence on the process and environment. If the process does not allow, should choose no vibration of the pump or take anti-vibration measures.

9. Cost factor. The cost of vacuum pump should consider the one-time purchase cost and comprehensive use cost. One-time costs, including the cost of the vacuum pump itself, the cost of peripheral pipeline supporting; Comprehensive use costs, including daily operation and maintenance costs, maintenance costs and service life costs.

10. Other special requirements. It mainly includes ac and dc power supply, power consumption, weight, volume, electronic control, heat dissipation, gas pipeline connection and specific requirements of various industries.

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