Freeze drying pressure parameter, how much is suitable for good result

Understanding how freeze-drying pressure changes at different stages of the drying process will enable you to use a freeze dryer proficiently. Therefore, this article will provide an in-depth analysis of pressure parameters to help customers easily understand the pressure changes within the freeze-drying chamber.

In a freeze-drying process, the freeze-drying pressure changes at each stage of product drying. Many users of this drying machine do not understand the logic behind the changes in parameters during the drying process, thus failing to monitor or identify problems when they occur. All parameters, including pressure, tray temperature, condenser temperature, solvent temperature, log temperature, etc., are interconnected according to specific rules. To understand these rules, users need to invest time in learning about them on this website.

The first image shows the machine in the freezing phase, displayed in the right corner of the white frame as DONG-25o, meaning it cools from room temperature to -25°C in about 4-6 hours. At this stage, the dryer has not yet created a vacuum, so the AP level is high.

The second image shows the cooling phase for the water condensation chamber. After freezing the product, the machine transfers the cooling to the condenser. When the condenser temperature reaches the set level, usually -40°C, the dryer moves to the next phase, which is the depressurization phase for the drying chamber, meaning the vacuum pump starts operating.

Image 3: The pressure reduction phase is the initial stage when the vacuum pump is activated. During this phase, the freeze-drying pressure gradually decreases to 120 Pa to allow for the next drying process, which involves heating the product to accelerate ice sublimation. In freeze-drying machines, this pressure reduction phase can be prone to errors such as leaky doors or valves, affecting the suction process. If the pressure doesn’t decrease sufficiently within a certain time, the machine will report an error, and the drying process will restart to prevent ice from melting on the product. Users need to check the opening and closing mechanisms.

Image 4: After the appropriate pressure reduction phase, when the pressure is below 120 Pa, the dryer switches to the actual product drying phase. The display in the right corner of the screen shows APS: 15°. This is the drying parameter for probiotics, so the maximum temperature on the product should not exceed 15°C. For other products such as fruits, vegetables, and Cordyceps mushrooms, the setting should be 30~45°C. The drying chamber pressure in this phase should be maintained within the range of 20~50 Pa for optimal results. The temperature on the product is then gradually increased until completely dry.

Image 5: These are the parameters when the product is completely dried. An AP of < 25 Pa is acceptable, and the temperature values ​​of the D-V-T-X sensors will approximate the APS. If, at this final stage, the freeze-drying pressure shows above 50 Pa, you need to check the pump oil and replace it with new oil to ensure the suction pressure meets the requirements.

Thus, with the basic information above, users of freeze dryers can now better understand how the freeze-drying pressure value changes during the product drying process. For further advice, please contact Mactech for appropriate information. Thank you for reading this information.