Vacuum pump oil selection requirements

- Dec 19, 2018-

1. Vacuum pump oil tightness
The vacuum pump oil needs a suitable viscosity, and the vacuum pump can be started at a low temperature. The vacuum pump oil can have a good sealing performance at a high temperature, and the vacuum pump oil has a low temperature rise in the pump. Does not contain light volatile components, reducing the return rate of the vacuum pump during operation.
2. Saturated vapor pressure of vacuum pump oil
Saturated vapor pressure is one of the key indicators of vacuum pump oil. In a constant temperature closed vessel, the pressure at which the vapor and liquid phases reach dynamic equilibrium is referred to as the saturated vapor pressure.
The saturated vapor pressure of the oil should be as low as possible. At the maximum operating temperature of the pump, it must have a sufficiently low saturated vapor pressure and be lower than the ultimate pressure of the vacuum pump. At least 6.5 × 10 -5 kPa is required at 60 ° C (the saturated vapor pressure drops by an order of magnitude for every 20 ° C rise in temperature rise).
3. Limit total pressure and limit partial pressure of vacuum pump oil
Ultimate full pressure: The sum of all the substances (gas) generated by the vacuum pump is measured by a Pirani meter or a thermocouple vacuum gauge. Foreign countries are currently focusing on test indicators for full pressure.
 Limit partial pressure: The limit air partial pressure of the pump measured by a mercury-tight vacuum gauge (Mcometer). The partial pressure of the two-stage rotary vane pump should be ≤6×10-5 kPa. The limit full pressure and the limit partial pressure difference request are not more than one order of magnitude. The greater the difference between the two, the more volatile components contained in the vacuum pump oil, and the worse the properties of the oil.
 (Note: The ultimate full pressure and ultimate partial pressure are stopped by a two-stage excellent vacuum pump)
 4, the smoothness of vacuum pump oil
 Friction and wear of the friction surface, wear and wear on the surface, and corrosion and wear are all related to smooth conditions. The excellent performance of the vacuum pump oil is beneficial to suppress corrosion and wear; it can effectively reduce the adhesive wear and the appearance of fatigue wear; the fluid smoothing agent has a cleaning effect on the friction surface and can also reduce the friction and wear. Reduce frictional resistance to save energy and reduce wear and tear to extend mechanical life.
5, vacuum pump oil cooling performance
Reducing the temperature of the friction surface is an important part of smoothness. When the friction surface moves, it is necessary to restrain the friction and work, and the work that is used to restrain the friction is all converted into heat, and as a result, the temperature of the friction surface rises. The amount of frictional heat is related to the smooth state. The heat with the highest viscosity is the largest, the heat with the low viscosity is the smallest, and the heat of the border friction is between the two. It can be seen that the vacuum pump oil with suitable viscosity can not only complete the smoothness of the liquid, reduce the generation of frictional heat, but also can bring the frictional heat out of the pump body in time.
6, the cleanliness of vacuum pump oil
 The friction pair must not be in contact with the surrounding medium, causing corrosion, rust and destruction. The excellent performance of the vacuum pump oil requires cleaning the friction area as much as possible; corrosion resistance and rust prevention and maintenance of the friction surface is not affected by oil enthalpy or external corrosion.
7. Oxidation stability of vacuum pump oil
Oxidation stability clarifies the anti-aging properties of smooth oils, and this special performance request is available for vacuum pump oils for industrial line operations. All smooth oils have different levels of auto-oxidation tendency depending on their chemical composition and external conditions. In the presence of air (or oxygen) and a metal catalyst, the vacuum pump oil exhibits an acid value, a viscosity change, and a precipitate formation in an oxidation time at a certain temperature. Oxidation will occur with the application process, so some aldehydes, ketones, acids and colloids, asphaltenes and the like are gradually formed, and oxidation stability is to suppress the above-mentioned properties which are not favorable for the use of oils.
8. Heat stability of vacuum pump oil
It indicates the high temperature resistance of the oil, that is, the resistance of the smooth oil to the heat synthesis, that is, the heat synthesis temperature. Some demanding vacuum applications require thermal stability for vacuum oils.
Natural mineral oil has its unpreventable defects, and its heat resistance is worse than that of synthetic oil. The composition of pump oil is easily degraded with thermal oxidation synthesis, the ultimate pressure stability is poor, and the pumping speed also drops with the application time. The ordinary pure mineral oil oxidation test method D943 is about several hundred hours, and the synthetic oil D943 can be extended to more than 3,000 hours. It can be seen that its service life has been extended.
9, the anti-emulsification of vacuum pump oil
During the operation of the vacuum pump, the moisture and cold air in the system are discharged into the pump oil. If the vacuum pump oil is not resistant to emulsification, it will form an emulsion with the mixed water, so that the water is not easily discharged from the bottom of the circulating oil tank. It is possible to form a vacuum drop and a poor smoothness.
Therefore, demulsibility is a very important physical and chemical property of industrial smooth oil. Especially in the pharmaceutical, food, ceramics and other industries using vacuum drying process, the anti-emulsification performance of pump oil is more important. The oil-resistant oil and water with good anti-emulsification ability can be strong, and the water vapor and condensed gas will discharge local water vapor after opening the gas ballast valve. In addition, low viscosity pump oil can be more resistant to emulsification than high viscosity pump oil.
10. Anti-foaming property of vacuum pump oil
During the operation of the vacuum pump, foam is often generated due to the presence of air. Especially when the oil contains an additive having a surface activity, the foam is more likely to be generated, and the foam is not easily lost. The use of foam in the smooth oil application will destroy the oil film, not only causing the friction surface to sinter or increase wear, but also promote smooth oil oxidation. During the operation of the vacuum system, the gas is discharged from the sealed vacuum pump oil layer from time to time, and the exhausted gas collar will generate a large amount of air bubbles on the outer surface of the oil layer and overflow from the vent hole of the pump to form oil loss and equipment pollution. The pump oil with anti-foaming agent has obvious progress in anti-foaming effect.