Vacuum pump oil selection guide

Vacuum pump oil is a vacuum pump accessory. When selecting vacuum pump oil, what should be paid attention to and what are the requirements? EVP vacuum pump manufacturer has made the following summary.

1. Oil seal performance of vacuum pump

Vacuum pump oil requires proper viscosity. At low temperature, the vacuum pump can start quickly. Under high temperature, vacuum pump oil can have good sealing performance. The pump temperature of the vacuum pump oil is low. rise. It does not contain light volatile components, which reduces the recovery rate of the vacuum pump during operation.

2. Saturated steam pressure of vacuum pump oil

Saturated vapor pressure is one of the key indexes of vacuum pump oil. In a constant temperature closed vessel, the pressure at which the vapor and liquid phases reach dynamic equilibrium is called saturated vapor pressure.

The saturated vapor pressure of the oil should be as low as possible. Under the high working temperature of the pump, it should still have enough low saturated vapor pressure and be lower than the limit pressure of the vacuum pump. At a temperature of 60, it must reach at least 6.5 × 10 – 5 kPa (the saturated vapor pressure drops by about an order of magnitude for every 20% increase in temperature).

3. Final total pressure and final partial pressure of vacuum pump oil

The sum of the pressure generated by the vacuum pump material (gas) measured by the Pirani instrument or thermocouple vacuum gauge. Foreign countries are now focusing on comprehensive stress test indicators.

Final partial pressure: the ultimate air partial pressure of the pump measured by the mercury compression vacuum gauge (mcometer), the partial pressure of the two-stage rotary vane pump shall be ≤ 6 × 10-5kpa. The limit full pressure and the limit differential pressure request shall not exceed one order of magnitude. The greater the difference between the two, the more volatile components in the vacuum pump oil, the worse the properties of the oil. (Note: the final total pressure and ultimate partial pressure are both stopped by two-stage advanced vacuum pump)

4. Smoothness of vacuum pump oil

Friction and wear of friction surface, surface fatigue and wear, corrosion and wear, etc. Both are related to smoothing conditions. The excellent performance of vacuum pump oil is conducive to the inhibition of corrosion and wear; it can effectively reduce the appearance of adhesive wear and fatigue wear; the fluid smooth agent has a clean effect on the friction surface, and can also reduce friction and wear. Reduce friction resistance to save energy, reduce wear and prolong mechanical life.

vacuum pump oil selection guide

5. Cooling performance and cooling performance of vacuum pump oil

It is important to reduce the temperature of friction surface. When the friction surface moves, friction and work must be suppressed, and all work used to suppress friction is converted into heat. As a result, the temperature of the friction surface rises. The friction heat is related to the smooth state. High viscosity heat, low viscosity heat is small, and boundary friction heat is between them. It can be seen that the vacuum pump oil with appropriate viscosity can not only complete the smoothness of the liquid, reduce the generation of friction heat, but also timely remove the friction heat from the pump body.

6. Cleanliness of vacuum pump oil

It can not prevent the friction pair from contacting with the surrounding medium, causing corrosion, rust and damage. The performance requirements of vacuum pump oil are to sweep through the friction area as far as possible, to prevent corrosion and rust, and to keep the friction surface free from oil or external corrosion.

7. Oxidation stability of vacuum pump oil

Oxidation stability clarifies the anti-aging property of smooth oil, which is the special performance requirement of vacuum pump oil for industrial assembly line operation. Smooth oils have different degrees of self oxidation tendency, which depends on their chemical composition and external conditions. In the presence of air (or oxygen) and metal catalyst, vacuum pump oil shows acid value, viscosity change and precipitate formation in oxidation time at a certain temperature. In the process of application, oxidation will occur, so some aldehydes, ketones, acids, colloids, asphaltenes, etc. will be formed gradually, and the oxidation stability is to inhibit the performance of the above unfavorable oil.

8. Thermal stability of vacuum pump oil

Indicates the high temperature resistance of oil, that is, the resistance of smooth oil to thermal synthesis, that is, the thermal synthesis temperature. Some demanding vacuum applications require thermal stability of vacuum oil.

Natural mineral oil has its inevitable defects, the heat resistance is worse than synthetic oil, the composition of pump oil is easy to deteriorate with thermal oxidation synthesis, the stability of limit pressure is poor, and the pumping speed also decreases with the use of time. The oxidation test method of common pure mineral oil D943 is about several hundred hours, and synthetic oil D943 can be extended to more than 3000 hours. It can be seen that its service life has been extended.

9. Anti emulsification of vacuum pump oil

During the operation of the vacuum pump, the water and cold air in the system will be discharged into the pump oil. If the demulsibility of vacuum pump oil is not good, mix it with mixed water. The emulsion makes it difficult for water to escape from the bottom of the circulation tank, which may lead to vacuum drop and 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 and water resistant oil and water with good anti emulsification ability can be very strong. After opening the valve, the water vapor and condensate will discharge local water vapor. In addition, low viscosity pump oil is more resistant to emulsification than high viscosity pump oil.

10. Defoaming performance of vacuum pump oil

In the process of vacuum pump operation, because of the existence of air, bubbles often occur, especially when the surface active additives in oil are more prone to foam, and bubbles are not easy to fade.

The use of foam in smooth oil will destroy the oil film. It will not only make the friction surface sintered or increase wear, but also promote the smooth oxidation and enthalpy change of the oil. During the operation of the vacuum system, the gas reservoir will be discharged from time to time through the sealed vacuum pump oil layer. Large amount of waste gas is produced on the outer surface of oil layer

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