A pressure-operated safety circuit for use in high-vacuum serum-drying plants

Abstract

The successful operation of the Greaves-Adair (1939) and similar processes for drying blood serum by sublimation from the frozen state depends on the maintenance of an adequate vacuum in the desiccating chamber. If the pressure in the region of the refrigerated condenser coils should rise materially above the operating range of 0 10-0 05 mm. Hg (the vapour tension of ice at -40 to -45°C.), the rate of sublimation from the frozen serum will diminish and the serum will tend to thaw.A rise in pressure may occur in one of two main ways. In the first place a fault in the mechanical refrigeration cycle may cause a rise in temperature and hence in water-vapour tension at the condenser surface.