How to Choose a Pump?
The function of a vacuum pump is to extract gas molecules from a vacuum chamber, reducing the gas pressure within to achieve the required vacuum level. Broadly speaking, the range from atmospheric pressure to vacuum is vast, and to date, no single vacuum system can cover this entire spectrum. Therefore, to meet the process specifications, operational efficiency, and equipment lifespan requirements of different products, distinct vacuum system configurations must be selected for different vacuum segments. To achieve an optimal configuration, the following points should be considered when selecting a vacuum system:
1. The ultimate pressure of the vacuum pump must meet the working pressure requirements of the process. Typically, the pump's ultimate pressure is selected to be approximately one order of magnitude lower than the process requirement.
2. Each 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 outside the permissible working pressure for extended periods.
3. At its operating pressure, the vacuum pump must be capable of removing the entire gas volume generated during the vacuum equipment's process.
4. Selecting vacuum pump units:
(1) When a single pump cannot meet the pumping and vacuum requirements, multiple pumps must be combined to complement each other and satisfy process demands.
(2) Some vacuum pumps cannot operate at atmospheric pressure and require a pre-vacuum; others discharge at sub-atmospheric pressure and need a backing pump. Therefore, pumps must be used in combination. A combination of vacuum pumps is termed a vacuum pump unit, enabling the vacuum system to achieve optimal vacuum levels and pumping speeds. Proper selection of the pump combination is crucial, as different vacuum pumps have distinct requirements for the gases they can handle. For example, Roots-rotary vane units are generally unsuitable for systems containing significant amounts of condensable gases.
5. When selecting oil-sealed pumps, first determine whether your vacuum system has oil contamination requirements. If equipment demands strict oil-free operation, choose oil-free pumps such as liquid ring pumps or cryogenic pumps. For less stringent requirements, oil-lubricated pumps can be used with contamination prevention measures—such as cold traps, oil traps, or baffles—to meet clean vacuum standards.
6. Identify the composition of the gas being evacuated: Does it contain condensable vapors, particulate matter, or corrosive substances? Selecting the appropriate vacuum pump requires knowledge of the gas composition. If the gas contains vapors, particles, or corrosive components, consider installing auxiliary equipment on the pump inlet line, such as condensers or dust collectors.
7. When selecting oil-sealed vacuum pumps, consider the environmental impact of oil vapors (oil fumes) emitted by the pump. If pollution is unacceptable, choose oil-free vacuum pumps or vent oil vapors outdoors.
8. Determine whether vibrations generated during pump operation affect the process or environment. If unacceptable, select vibration-free pumps or implement anti-vibration measures.
9. Vacuum pump price, operating costs, and maintenance expenses.
Only after considering all these factors can a solution best suited to your needs be finalized:
(1) Minimal investment costs.
(2) Lowest possible production operating expenses.
(3) A feasible solution that reasonably balances the first two factors.
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