How to Choose a Pump

所属分类： How to Choose a Pump

发布时间： 2021-02-26

概要：

The function of a vacuum pump is to extract gas molecules from the vacuum chamber, thereby reducing the gas pressure inside the chamber and achieving the desired degree of vacuum. Generally speaking, there is a wide range—from atmospheric pressure down to extremely high vacuum—and to date, no single vacuum system can cover this entire range. Therefore, to meet the process requirements, efficiency goals, and service life expectations of different products, it is necessary to select different vacuum system configurations for various vacuum segments. To achieve the optimal configuration, the following points should be considered when choosing a vacuum system:

1. The ultimate pressure of the vacuum pump should meet the working pressure required by the process. Typically, the pump’s ultimate pressure is selected to be about one order of magnitude lower than the process requirements.

2. Each type of pump has a specific operating pressure range; therefore, the pump’s operating point should be selected within this range and it should not be allowed to operate for extended periods beyond its maximum allowable working pressure.

3. Under its operating pressure, the vacuum pump should be able to exhaust the entire volume of gas generated during the process in the vacuum equipment.

4. Select the vacuum unit:

(1) When a single pump cannot meet the requirements for pumping and achieving vacuum, several pumps need to be combined and used in tandem to complement each other and satisfy the process demands.

(2) Some vacuum pumps cannot operate at atmospheric pressure and thus require a preliminary vacuum stage; others have outlet pressures lower than atmospheric pressure and therefore need a forepump. Consequently, these pumps must be combined for use. A vacuum pump system composed of such combined pumps is referred to as a vacuum pump unit. Such a unit can achieve better vacuum levels and higher pumping speeds in the vacuum system. We should select the appropriate combination of vacuum pumps carefully, since different vacuum pumps have varying requirements for the gases they can effectively remove. For example, under normal circumstances, a Roots-rotary vane pump combination is not suitable for systems containing large amounts of condensable gases.

5. When selecting an oil-sealed pump, you should first determine whether your vacuum system has specific requirements regarding oil contamination. If the equipment strictly demands oil-free operation, you should opt for various oil-free pumps, such as liquid-ring pumps or cryogenic pumps. However, if the requirements are not stringent, you can choose oil-sealed pumps and supplement them with certain measures to prevent oil contamination—for example, installing cold traps, oil traps, or baffles—to still meet the cleanliness requirements of the vacuum system.

6. Understand the composition of the gas being pumped, whether the gas contains condensable vapors, particulate dust, or corrosive substances. When selecting a vacuum pump, it is essential to know the gas composition and choose a pump that is specifically suited to the gas being pumped. If the gas contains vapors, particles, or corrosive gases, you should consider installing auxiliary equipment—such as condensers or dust collectors—in the pump’s inlet pipeline.

7. When selecting an oil-sealed vacuum pump, you should consider the impact of oil vapor (fumes) emitted by the pump on the environment. If the environment cannot tolerate any pollution, you should choose an oil-free vacuum pump or ensure that the oil vapor is vented outdoors.

8. Does the vibration generated during the operation of the vacuum pump affect the process or the environment? If the process does not permit such vibration, a pump that produces no vibration should be selected, or vibration-reducing measures should be implemented.

9. The price of the vacuum pump, as well as its operating and maintenance costs.

Only after considering all possible scenarios can we finally determine a solution that’s right for you.

(1) The lowest investment cost.

(2) The lowest production operating costs.

(3) A feasible solution that reasonably and evenly distributes the first two scenarios.

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关键词： How to Choose a Pump

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