A freeze dry unit having several novel features is the subject of this vacuum freeze dryer. A plurality of shelves are placed in the drying unit and are coupled with cables which serve to interconnect three points on each shelf. This assures that an upward force applied at any point on the shelf will be distributed over the entire shelf and the shelf will rise in a true horizontal plane. An improved refrigeration system is also provided which incorporates an auxiliary capillary tube that can be bypassed by a solenoid valve or used to reduce the volume of refrigerant flowing through the system thereby decreasing the load on the compressor.
Food drying equipment is a technique well known to those skilled in the art for preserving both plant and animal biological materials. For relatively small production or laboratory requirements, so-called "fluid bed dryer" have long been in use. These units are normally relatively small and are designed to freeze dry and stopper a large number of small vials or other "laboratory size" vessels. It is known in the art to utilize movable shelves inside of a stoppering tray dryer along with an inflatable bladder which raises one or more shelves until the stoppers on the vials of the shelf being raised contact the horizontal shelf or frame section immediately above it thus forcing the stoppers into sealing relationship with the vial.
Another difficulty with drying equipment of the type that have heretofore been commercialized is the need to size the refrigeration compressor to handle maximum cooling requirements, namely those required to effect the initial freezing of the sample. This means that once the sample is frozen and a vacuum is applied, there is excess refrigeration capacity because of the lowered pressure inside of the dryer.
It is also one of the objects of the vacuum freeze dryer to provide an improved locking mechanism for the door of a stoppering tray dryer which provides a more reliable seal than previous locking mechanisms as a result of applying the locking mechanisms as a result of applying the locking force at the center of the door.
by: wan
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