Vacuum pump oils FAQ

Why is the anti-emulsification property (water separability) of rotary vacuum pump oil necessary?

If a pump absorbs water such as water vapor, condensation will form within the pump. This condensation mixing into the oil will subject the oil to emulsification. In this situation, if the water is not quickly separated from the oil, a large amount of gas (water vapor) is released from the high quality vacuum side and the ultimate pressure increases, or the inside of the pump is corroded. Therefore, it is desirable for an oil to have good water separability and be easy to drain of water.

Why is vacuum pump oil heat resistance necessary?

To lower the ultimate pressure, oils that have excellent heat resistance, that is, oils that release a small amount of gas due to thermal decomposition, are required.
Also, oils with favorable properties such as heat resistance are required in order to reduce the frequency of oil changes (to increase the service life of the oil).

What is the meaning of the ultimate pressure of a vacuum pump oil?

The ultimate pressure refers to the lowest pressure that can be obtained at a steady state when using vacuum pump oil to actually operate a vacuum pump and thoroughly exhausting the gases. The oil steam pressure must be lower than the pump's limit ultimate pressure.

What is the meaning of the exhaust velocity of oil diffusion pump oil?

This indicates the exhaust capability of the diffusion pump. Basically, this capability is determined by the structure of the diffusion pump, but the molecular weight of the oil diffusion pump oil also has an effect. If the molecular weight is too small, the steam pressure will become too high. On the other hand, if the molecular weight is too large, the exhaust velocity will decrease.

What are some of the causes of decreased rotary pump oil service life? What are some corresponding counter-measures?

There are a great number of causes, but some examples are shown below.
• Decrease in the degree of vacuum due to the suctioned gas (a substance with high steam pressure such as a solvent or water)
If a small quantity of these substances is suctioned, the substances can be removed. But if a large quantity is suctioned and cannot be separated from the oil, replace the oil.
• Oxidation degradation caused by usage with a low degree of vacuum
Strengthen the external cooling of the vacuum pump or replace the oil with one that excels in terms of stable heat resistance and oxidation resistance.
• Thermal degradation caused by the suction of a gas at an extremely high temperature
Attach a cooler on the suction side of the vacuum pump or replace the oil with one that excels in terms of stable heat and oxidation resistance.
 (Such as NEOVAC SO-M, NEOVAC ST-200, or NEOVAC MR-200A )
• Contamination caused by the suction of powders or solid objects
Use a filter outside of the system to remove through circulation the solid objects that have entered into the vacuum pump oil and attach a filter to the suction side.
• Degradation caused by the suction of corrosive gases (fluorine and chlorinated gases)
Our current idea is to use an active filter to remove the gases, but there are limits to how effective this is, and we cannot guarantee that it will eliminate all damage caused by the gases.

effect does this have on the pump?

There are a number of different causes of this degradation, some of which are shown below.
1) Thermal degradation caused by overheating past the operating temperature
2) Thermal degradation caused by the application of heat with insufficient oil applied
3) Oxidation degradation caused by contact with air while the oil is at a high temperature (100°C or more)
4) Degradation caused by contact and mixing with suctioned objects from the vacuum equipment Oil degradation can lead to phenomena such as decreased exhaust velocity, inferior ultimate pressure, and uneven pressure caused by decomposition products.

What is the structure of a rotary pump?

Rotary pumps are constructed of a cylinder as well as the rotor and its blades that rotate within the cylinder. There are three types of rotary pumps, which are divided on the basis of how the rotor is attached to the rotating shaft and the differences in blade shapes.
As a description of a representative rotating-blade-type rotary pump, the rotor rotates around the shaft at its center and the blades attached to the rotor come in contact with the cylinder wall as they rotate, which compresses the air that has entered into the pump from the suction inlet. A valve is present at the outlet. The compressed air presses against the valve and is then evacuated out into the atmosphere. Repetitions of this process are used to create a vacuum at the inspiration side.

What is the purpose of rotary pump oil?

With a rotary pump, it is not possible to exhaust all the compressed air that exists in the vicinity of the exhaust valve. Due to the pump construction, there remains air that cannot be completely compressed. This is known as "invalid air," and so long as this exists, the degree of vacuum cannot improve past a certain level.
In this situation, if rotary pump oil is fed into the pump, the oil fills in the space that was taken by the invalid air. What's more, the oil is not compressed, so air that remains as invalid air is further reduced. As a result, the degree of vacuum can be improved.
In addition, the oil works as a lubricant for the cylinder, blades, and rotor to enable the moving parts to slide past each other more smoothly.

What is the structure of an oil diffusion pump and what is the purpose of oil diffusion pump oil?

Oil diffusion pumps are constructed of a boiler part, a jet part, and a cylinder part. There are no parts that are made to move mechanically.
Oil diffusion pump oil is heated by the electric heater of the boiler part until the oil is converted to steam. This steam is then sprayed from the nozzles of the jet part. Gas molecules that enter through the suction inlet are struck by the jets of oil steam molecules, whose momentum is conveyed to the gas molecules. These gas molecules are thusly compressed down to the bottom of the chamber. At the same time, the gas molecules are transported from the exhaust port to the supplemental pump (in most cases a rotary pump). As a result, a vacuum is obtained in the suction system. On the other hand, the oil steam molecules that strike the inner walls of the cold cylinder condense into a liquid, return to the boiler part, and are once more heated and sprayed from the nozzles.