SPI Critical Point Drying Apparatus

The pressure vessel and water jacket are made from a solid brass cylinder of diameter 3¼"(8.25 cm) and length 5" (12.7 cm). Machining, literally, from a solid piece of metal gives reliable mechanical properties under high pressure conditions and the use of brass ensures good thermal transfer properties.

The internal diameter of the pressure vessel (i.e. the diameter of the pressure chamber) is slightly under 1¼" (3.18 cm) giving a wall thickness of over 2" (5.1 cm). The wall contains narrow-bore water passageways which act as an integral water jacket for heating and cooling. The ends of the water jacket are sealed by two annular end plates which do not cover the ends of the pressure chamber. Two connectors are screwed into the outside wall of the vessel and connect with the water channels.

Both ends of the pressure chamber are internally screw threaded. The specimen loading door screws into one end; the viewing window is held in the other end by a retaining ring. A ½" (1.27 cm) thick Perspex ^® shield acts as an explosion guard over the toughened glass (½"/5.1 cm thick) viewing window. For those not familiar with the trade name Perspex, it is the trade name belonging to ICI to describe their brand of cast acrylic sheets. Another commonly used cast acrylic sheet that could have been used is Plexiglas ^®, made by Rohm & Haas, or Lucite ^® sheet made by DuPont.

Servicing

To replace glass viewing window:

1. Unscrew the four hexagon socket screws and remove the Perspex guard.
2. Unscrew the slotted retaining ring (but whatever you do, do not disturb the chromium plated annulus which covers the water jacket)
3. Check the 'O' ring in the retaining ring.
4. Remove the viewing window and the Dowty^® seal. If hardened or damaged, the seal should be replaced.
5. Reassemble the unit in reverse order taking care not to damage the edge of the glass window.

1. Remove four hexagon socket screws.
2. Pry end plate off body.
3. Thoroughly clean all surfaces.
4. Replace new cork gasket and nylon screw seal.
5. Screw end plate firmly to body.

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