Laboratory freeze dryer

Claim 2

Vacuum trap apparatus useful as a laboratory freeze dryer comprising: a. inner and outer shells forming a closed spaced therebetween which can be evacuated, said inner shell being metallic and providing a condensing surface on which vapors from the goods being freeze dried are condensed; b. valved means for introducing a gas under pressure into said inner shell adjacent the bottom thereof, said gas expanding in said inner shell to form a snow for cooling the walls of said inner shell, and c. control means acting to open and close said valve means responsive to the level of snow in said inner shell respectively falling below and reaching a predetermined level for controlling the introduction of said gas into said inner shell and maintaining the level of snow at substantially said predetermined level.

Claim 3

Apparatus as set forth in claim 1 wherein said valved means includes: a. a gas line having one end extending down into said inner shell and terminating in an outlet nozzle adjacent the bottom thereof, the other end of said line being connectable to a source of pressurized gas; and b. a flow control valve intermediate said ends.

Claim 4

Apparatus as set forth in claim 1 wherein said valved means includes a gas line having an outlet opening into said inner shell adjacent the bottom thereof, said control means including a piston in said inner shell disposed above said gas line outlet, said piston moving responsive to the level of snow in said inner shell to open and close said valved means.

Claim 5

Apparatus as set forth in claim 3 including a pad of porous material disposed above said piston to seal against the passage of snow while permitting the passage of sublimating gas.

Claim 6

Apparatus as set forth in claim 4 wherein said porous material rests on and moves with said piston.

Claim 7

Apparatus as in claim 3 including a micro switch operatively connected to said piston and valved means wherein movement of said piston beyond predetermined limits opens and closEs said switch to operate said valved means.

Claim 8

Apparatus as in claim 6 including a cover for said inner shell, said switch being mounted on said cover.

Claim 9

Apparatus as in claim 7 including a rod upstanding from said piston, said rod adapted to pass through an opening in said cover responsive to movement of said piston for operating said switch.

Claim 10

In a laboratory freeze dryer comprising an inner and an outer shell adapted to be joined so that the space therebetween can be evacuated, the inner shell forming a reservoir for the containment of a cooling medium and presenting a super cooled condensing surface to said space, the improvement comprising: a. valved means for introducing pressurized carbon dioxide into the reservoir formed by said inner shell, the expansion of said pressurized carbon dioxide in said inner shell forming a snow therein to cool said condensing surface; b. a piston in said inner shell, said piston rising and falling in said inner shell responsive to the level of carbon dioxide snow therein; and c. control means operatively connected to said piston and valved means and operating to close and open said valved means in response to movement of said piston between predetermined high and low level limits respectively, for maintaining the level of said snow at a substantially constant level between said limits.

Claim 11

In a laboratory freeze dryer comprising an inner and an outer shell adapted to be joined so that the space therebetween can be evacuated, the inner shell forming a reservoir for the containment of a cooling medium and presenting a super cooled condensing surface to said space, the improvement comprising: a. valved means for introducing pressurized carbon dioxide into the reservoir formed by said inner shell, the expansion of said pressurized carbon dioxide in said inner shell forming a snow therein to cool said condensing surface; b. a piston in said inner shell, said piston rising and falling in said inner shell responsive to the level of carbon dioxide snow therein; and c. control means operatively connected to said piston and valved means and operating to close and open said valved means in response to movement of said piston between predetermined high and low level limits respectively, for maintaining the level of said snow at a substantially constant level between said limits.