Vacuum is the absence of gases like air, and water vapor, and in a freeze drying system is produced to enable water molecules unimpeded travel from the product to the condensing surface.  Vacuum pressure must be maintained during the primary and secondary drying phases of the process of freeze drying.  Maintenance of vacuum depends upon many factors which include, integrity of the drying system envelope [pipe connections, welds, valves, gaskets, seals, chambers], and also the condition of the vacuum pumping system. Product contamination can be caused by back streaming, which is a phenomenon that allows vacuum pump oil to move by diffusion into the freeze drying chamber and potentially contaminate product being dried, during some portions of cycles.  There are many sorts of vacuum pumps, and vacuum systems, which are both complex to maintain, and difficult to understand when a vacuum fails to be established at the right time, and at the appropriate pressure during the process.

The capacity of a condenser for pumping or trapping water vapor is much higher than water removal than typical vacuum pumps installed on freeze dryers.  A rule of thumb is that one square inch of condensing surface below -40 DegC is equivalent to a 100 CFM vacuum pump’s water vapor pumping capacity.  A typical condenser in a production sized freeze dryer has a condensing surface that may be equivalent to or larger than the shelf area of the freeze dryer.  So, a 100 square foot freeze dryer, has a condensing surface that is 100 square feet. If the rule of thumb is followed there are 14400 square inches of surface, or the equivalent of that many 100 CFM vacuum pumps.  So, adding a bigger vacuum pump to a poorly designed system [i.e. one that has an inadequate condenser surface area] is ineffective and a waste of energy. 

Whether you need hands on training in vacuum pump maintenance, leak checking, elimination of back streaming, someone to trouble shoot your system, you can rely upon Applewood Scientific as your resource to evaluate, educate, and train your personnel in all aspects of vacuum,