Oil drying, there is a way to blow dry the operating (compressed) air above the exhaust valve. It is quite effective to remove water from fine mist oil emulsion in exhaust pipe by dry coal air. This method is especially suitable for the small single-stage claw vacuum pump whose pressure is lower than 5 Torr, because this method is different from the gas stabilization method and will not affect the inlet pressure of the claw vacuum pump. When the working pressure is lower than 5 Torr, the air used is about 5% of that of the claw vacuum pump, and it can be reduced with the decrease of the working pressure. The higher the working temperature of claw type vacuum pump is, the drier and hotter the air for water removal is, and the better the degree of oil purification is. For claw type vacuum pump, this method is not used.
Claw type vacuum pump oil of selection requirements
1. Sealing property of claw type vacuum pump oil
The claw type vacuum pump oil needs to have the suitable viscosity, which can make the claw type vacuum pump start quickly at low temperature. The claw type vacuum pump oil can have good sealing performance at high temperature, and the claw type vacuum pump oil has low temperature rise in the pump. It does not contain light volatile components, which can reduce the oil return rate of claw vacuum pump.
2. Saturated vapor pressure of claw vacuum pump oil
Saturated vapor pressure is one of the key indexes of claw vacuum pump oil. In a closed vessel with constant temperature, when the vapor-liquid two phases reach dynamic equilibrium, the pressure is called saturated vapor pressure.
3. Limiting total pressure and limiting partial pressure of claw type vacuum pump oil
Limit total pressure: the total pressure of all materials (gases) in claw vacuum pump measured by Pirani meter or thermocouple vacuum gauge. At present, foreign countries pay attention to the test index of full pressure.
Limit partial pressure: the limit air partial pressure of the pump measured by mercury contraction vacuum gauge (Maxwell’s meter), and the partial pressure of double-stage rotary vane pump shall be ≤ 6 × 10-5kpa. The difference request between the limit full pressure and the limit partial pressure is not more than one order of magnitude. The greater the difference between the two, the more volatile components in claw vacuum pump oil are, and the worse the properties of the oil are.
(Note: the two-stage claw type vacuum pump is used to stop the test for the limit full pressure and limit partial pressure)
4. Smoothness of claw type vacuum pump oil
The friction wear, surface fatigue wear and corrosion wear of the friction surface are all related to the smooth condition. Good performance of claw type vacuum pump oil is beneficial to prevent corrosion and wear; it can effectively reduce adhesive wear and external fatigue wear; fluid lubricant can clean the friction surface and reduce friction and wear. Reduce friction resistance to save energy, reduce wear and prolong mechanical life.
5. Cooling performance of claw vacuum pump oil
Reducing the temperature of friction surface is an important function of smoothness. When the friction surface moves, it is necessary to work against the friction force, and all the work consumed in restraining the friction force is converted into heat, which will cause the temperature of the friction surface to rise. The heat of friction is related to the smooth state, the heat of high viscosity is the largest, the heat of low viscosity is the least, and the heat of boundary friction is between the two. It can be seen that the claw vacuum pump oil with suitable viscosity can not only smooth the liquid and reduce the generation of friction heat, but also take the friction heat out of the pump body in time.
6. Detergency of claw vacuum pump oil
Friction pairs can not be prevented from contacting with the surrounding media, causing corrosion, corrosion and damage. The excellent claw type vacuum pump oil should be cleaned as far as possible to remove the scale on the friction area; anti-corrosion and anti rust, and maintain the friction surface from oil degeneration or external corrosion.
7. Oxidation stability of claw vacuum pump oil
Oxidation stability clarifies the anti-aging properties of smooth oil, and has special performance requirements for claw vacuum pump oil for industrial pipeline operation. All smooth oils have different levels of automatic oxidation tendency depending on their chemical composition and external conditions. In the presence of air (or oxygen) and metal catalyst, the claw type vacuum pump oil will show the changes of acid value, viscosity and sediment formation during the oxidation time at a certain temperature. Oxidation will occur along with the application process, so some aldehydes, ketones, acids, resins, asphaltenes and other substances will be gradually generated. Oxidation stability is the performance of inhibiting the formation of the above substances which are not conducive to the use of oil products.
8. Heat stability of claw vacuum pump oil
It indicates the high temperature resistance ability of oil, that is, the resistance ability of smooth oil to thermal synthesis, that is, the thermal synthesis temperature. Some harsh vacuum application environment will put forward the request of thermal safety of vacuum oil.
9. Demulsibility of claw vacuum pump oil
During the operation of claw type vacuum pump, the water and cold air in the system will be discharged into the pump oil. If the anti emulsifying property of claw type vacuum pump oil is not good, it will form emulsion with mixed water, so that the water is not easy to discharge from the bottom of the circulating oil tank, so as to form vacuum drop and poor smoothness.
10. Antifoaming property of claw vacuum pump oil
During the operation of the claw vacuum pump, air bubbles often occur, especially when the oil contains active additives, and it is more likely to generate foam, and the foam is not easy to disappear. The use of foam in smooth oil will destroy the oil film, not only cause the friction surface to attack or increase wear, but also promote the oxidation and transformation of smooth oil. During the operation of the vacuum system, the gas in the vacuum system will be discharged from time to time through the sealed claw type vacuum pump reservoir. The discharged gas will generate a large number of bubbles on the surface of the oil layer, and overflow from the exhaust hole of the pump, resulting in oil loss and equipment pollution. The anti foam effect of pump oil with antifoaming agent has been improved obviously.