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Rotary Vane Vacuum Pump Ultimate Vacuum Instability factors

Limit vacuum refers to the lowest vacuum pressure that a pump can achieve under stable working conditions. It can reach its lowest pressure range soon after the pump is opened. After a period of operation, the increase of pump temperature will lead to the change of saturated vapor pressure and viscosity of lubricating oil. Limit vacuum pressure will fluctuate slightly, but it will fluctuate slightly. After a period of operation, it will tend to a stable vacuum pressure value. This stable value is what we usually call the limit pressure of vacuum pumps. The unstability of vacuum pump pressure is influenced by many factors, such as pumping time, lubricating oil, processing accuracy of pump itself, gap adjustment between pump parts and harmful space.


1. Effect of Vacuum Pump Oil on Vacuum Pump


For the height of the vacuum pump oil, that is, the circulating oil quantity of the pump. The greater the circulating oil quantity of rotary vane vacuum pump, the better the sealing effect and the lower the limit pressure. However, because the air and steam absorbed in the vacuum pump oil of rotary vane pump will release to affect its limit pressure during the operation of vacuum pump, the greater the circulating oil quantity, the better the sealing effect, and there should be an appropriate value.


The relationship between oil circulation and the limit pressure of rotary vane pump is as follows:


Among them, DE is the relationship between the circulating oil quantity and the limit pressure under the ideal condition (oil does not release air and water swallow gas), that is, the larger the vacuum pump oil is, the lower the limit pressure is: FG is the relationship between the vacuum pump oil and the limit pressure under the actual situation (mainly considering the release of air and water vapor). With the increase of the circulating oil quantity, the relationship between the vacuum pump oil and the limit pressure is getting higher and higher. When the oil quantity is at a certain value, the limit pressure is the lowest. Then it increases with the increase of oil quantity.


With the increase of the vacuum pump oil, the saturated vapor pressure of the oil also increases, and the volatile gas oil also increases greatly, so the limit pressure of the rotary vane pump should be lowered as much as possible to reduce the limit pressure of the rotary vane pump. At present, the main methods adopted by Yazhi Reed's mechanical and electrical technology include water cooling or air cooling of pump oil, increasing radiator and so on.


2. The influence of harmful space on the limit pressure of vacuum pump


The existence of harmful space also increases the limit pressure of rotary vane vacuum pump. The harmful space refers to the space between the contact point a of the rotor and stator of the rotary vane vacuum pump at the top of the stator chamber and the exhaust port. At the end of the cycle, it is difficult for the gas in this space to be discharged from the exhaust port. Under the compression action of the continuous rotation of the rotary vane, it will overflow from the clearance of point a contact point, and the overflow gas from the vertex enters the suction chamber, thus raising the limit pressure of the rotary vane vacuum pump. It can be solved by filling the harmful space with oil or opening the air groove on the side plate of the space (used in the self-lubricating dry pump).


3. Effect of Clearance on Limit Pressure of Vacuum Pump


The clearance of rotary vane vacuum pump refers to the clearance between the apex and the section. Clearance has a great influence on the limit pressure of good Kaide rotary vane vacuum pump. The existence of clearance is inevitable, which is related to the processing accuracy and assembly accuracy in the production process of rotary vane pump, and is also the need of functional design. Excessive clearance will cause the gas in the high-pressure chamber of rotary vane pump to drain into the low-pressure chamber, which will seriously affect the limit pressure of rotary vane vacuum pump. Although small clearance can reduce the limit pressure of rotary vane pump, it will lead to the increase of friction, which will lead to a series of problems such as power, wear and heat dissipation. So it is important to determine a reasonable gap. The clearance value is not the smaller the better. Generally, the clearance value should consider not only lubrication and leakage, but also thermal expansion.

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2XZ Direct Drive Rotary Vane Vacuum Pump

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