Owing to the introduction of vacuum technologies in many industrial areas, it is necessary to use vacuum generating devices and working fluids for them. Without high-quality working vacuum fluids, it is impossible to create a vacuum, because the degree of the achieved vacuum to a significant extent depends on the exploitation properties. When choosing a vacuum liquid, it is necessary to take into account the characteristics of the pumps, the compatibility of the liquids with the equipment for pumping it, the pumped out medium and the sealing materials of the structure.
Vacuum oil must have reduced vapor pressure at operating temperatures in the pump and thermal stability, and be chemically inert to the pumped gases and oxygen in the air.
Basically, vacuum oils are used in volumetric vacuum pumps (oil-sealed mechanical pumps, high-vacuum steam, steam-jet, steam boosters and for filling liquid vacuum gauges). In vacuum technology, vacuum organosilicon and mineral oils are often used.
When choosing a vacuum liquid, in addition to the characteristics of the pumps, it is also necessary to take into account the compatibility of the liquid with pumping equipment, the pumped out medium and sealing materials. For example, due to the use of vacuum oil for mechanical pumps, the sealing of the working chambers is improved, and power losses due to friction are reduced. The quality indicators of vacuum oils for mechanical pumps are assessed according to the following criteria:
- sufficiently low pressure of saturated vapors (it affects the degree of attainable vacuum and oil volatility);
- increased hydrolytic stability when pumping out air and vapors;
- optimal viscosity in certain cases (it indirectly determines the sealing and lubricating properties of working fluids);
- environmental safety;
- low gas solubility.