What are the criteria for selecting an oil-free dry vacuum pump?

BOKE VAC

Oil-free dry vacuum pumps offer significant advantages in energy efficiency and environmental protection, representing the future trend of the pump industry. Many oil-free dry vacuum pumps come with varying vacuum performance characteristics and distinct functional features. To select the appropriate model for your specific process requirements, it is essential first to understand the key considerations involved in choosing among different types of oil-free dry vacuum pumps. This informed selection helps you acquire the most suitable pump, reduce procurement costs, and ensure stable vacuum conditions—yielding substantial economic benefits for your enterprise. Now, let us delve into the detailed guidelines for selecting an oil-free dry vacuum pump.

Most users’ oil-free dry vacuum pumps are retrofitted from their former oil-sealed and liquid-ring vacuum pumps. So why are an increasing number of corporate customers opting to replace their traditional oil-sealed or liquid-ring vacuum pumps with dry, oil-free models?

Dry oil-free vacuum pumps operate without oil or water in the working chamber, thereby avoiding contamination of the vacuum chamber or the extraction medium. With fewer auxiliary components, they can also be vented directly to the atmosphere. Although their initial purchase cost is higher than that of conventional vacuum pumps, dry oil-free vacuum pumps offer significantly lower operating and maintenance expenses over time, with the cost advantage becoming increasingly pronounced as usage duration increases.

An oil-free dry vacuum pump is a dry, contactless, constant-pitch screw-type vacuum pump. The two screws are dynamically balanced and supported by bearings, with the entire assembly housed within the pump casing. A small clearance exists between the screws, ensuring stable operation without mechanical interference and eliminating any working fluid in the pumping chamber. Consequently, this oil-free dry vacuum pump can handle gases containing significant amounts of condensable vapors and particulates. It is an environmentally friendly, energy-efficient vacuum pump that outperforms oil-sealed mechanical vacuum pumps, liquid-ring vacuum pumps, reciprocating vacuum pumps, and other conventional models.

The selection criteria for dry vacuum pumps are as follows:

1. A dry vacuum pump shall be capable of exhausting all gases generated during the operation of the vacuum pumping system at its rated working pressure.

2. Each pump has a specific operating pressure range. Therefore, the pump’s operating point should be selected within this range, rather than allowing it to run continuously at the maximum allowable pressure.

3. The ultimate pressure of a dry vacuum pump shall meet the process’s operating pressure requirements. Typically, the pump’s ultimate pressure is approximately one order of magnitude lower than the process requirement.

4. Select the vacuum system:

(1) Determine the composition of the gas to be pumped, whether it contains condensable vapors, whether particulate matter is present, and whether it is corrosive. When selecting a dry vacuum pump, it is essential to know the gas composition and choose a pump type that is suitable for the specific gas being handled. If the gas contains vapors, particulates, or corrosive components, consider installing auxiliary equipment—such as condensers or dust collectors—in the pump’s inlet line.

(2) Do the vibrations generated by the dry vacuum pump during operation affect the process or the environment? If such vibrations are unacceptable, a vibration‑free pump should be selected, or vibration‑mitigation measures should be implemented.

5. When selecting an oil-sealed pump, the first step is to determine whether the vacuum system has oil‑contamination requirements. If the equipment mandates an oil‑free environment, non‑oil pumps—such as liquid‑ring pumps or cryogenic pumps—should be chosen. If the requirements are less stringent, oil‑sealed pumps may be used; additionally, various measures to prevent oil contamination—such as installing cold‑trap bends, oil‑separating bends, and baffles—can also help meet cleanliness‑related vacuum specifications.

6. When a single pump cannot meet the required pumping capacity and vacuum level, multiple pumps must be combined to complement one another, thereby satisfying the process requirements.

7. When selecting an oil-sealed vacuum pump, consider the environmental impact of the oil vapor (oil mist) discharged by the pump. If environmental contamination is unacceptable, choose an oil-free vacuum pump or vent the oil vapor to the outdoors.

8. Some vacuum pumps cannot operate at atmospheric pressure and require a preliminary vacuum; certain dry‑type vacuum pumps have outlet pressures below atmospheric pressure and thus necessitate a backing pump, requiring their combined use. Such integrated vacuum pump systems, known as vacuum pump units, enable the vacuum system to achieve higher vacuum levels and greater pumping speeds. We should select the appropriate configuration accordingly.