This article will provide a detailed introduction to the relevant knowledge of freeze dryer vacuum pumps, covering their principles and classifications.
I. Working Principle
The main function of a freeze dryer vacuum pump is to extract air from inside the freeze dryer, creating a low-pressure environment. This allows the water in the material to sublimate at low temperatures, achieving the drying purpose. Its principle is mainly based on the rarefaction and compression process of gases. When gas is drawn into the vacuum pump, as the pressure decreases, the average free path of gas molecules increases, and the collisions between gas molecules decrease, thus gradually rarefying the gas. When the gas is rarefied to a certain extent, it can be discharged out of the pump through a compression process, thereby maintaining the vacuum state inside the freeze dryer.
II. Types of Vacuum Pumps
According to their working principles and structural characteristics, freeze dryer vacuum pumps are mainly divided into oil-sealed vacuum pumps and oil-free vacuum pumps.
1. Oil-Sealed Vacuum Pumps
There are two types of oil-sealed mechanical vacuum pumps: rotary vane type and sliding vane type. The most commonly used in freeze dryers is the rotary vane pump. The parts are sealed and lubricated by an oil film of vacuum pump oil. To improve the ultimate vacuum, it is generally composed of two pumps connected in series to form a two-stage pump.
Rotary vane vacuum pumps compress the gas during operation. If the gas contains a large amount of water vapor, the water vapor will be compressed into small water droplets and mixed into the vacuum pump oil, causing the vacuum pump oil to emulsify, affecting the sealing performance of the pump, and thus affecting the ultimate vacuum of the pump. Therefore, a gas ballast valve is installed on the oil-sealed vacuum pump. Before the compression reaches the end point, the compressed gas is connected to the outside, reducing the compression ratio and thus reducing the amount of water entering the vacuum pump oil. The opening degree of the gas ballast valve can be adjusted or completely closed; when the gas ballast valve is opened, it will reduce the ultimate vacuum of the vacuum pump and increase the consumption of vacuum pump oil.
2. Oil-Free Vacuum Pumps
Vacuum pumps that use a working medium in the pump chamber will have the vapor molecules of the working medium evaporate and diffuse into the vacuum system, contaminating the vacuum system; this is not allowed for strictly regulated pharmaceutical machinery. Dry pumps, however, can operate without a working medium. Dry pump systems are clean vacuum systems with no oil or other liquid media in the pump chamber, thus preventing any contamination of the contents of the evacuated container; the exhaust port is free of oil mist, preventing environmental pollution; they have a strong pumping capacity for condensable gases such as alcohol and water vapor; and they have low maintenance costs, requiring no oiling or oil changes.