Abstract: An adjustable sanitary impellor hub device having a hub, a tapered, split collet, a locking collar and multiple seals. Impeller blades are attached to a hub that may be slid over an agitator shaft to a desired position. A tapered, split collet engages with a tapered inner cylindrical bore of the locking collar as the locking collar and hub are forced together, clamping the collet to shaft. At the same time, the outer surface of the locking collar engages with the hub, locking all three elements to the shaft. The multiple soft seals ensure that there are no dead spaces.

Abstract: A method and an apparatus for controlling the concentration of oxygen and pH of a medium during a bioreaction process in a vessel. The method and apparatus are particularly adapted to a fermentation process. A dissolved oxygen sensor generates a signal corresponding to the pH of the medium and a dissolved oxygen sensor generates a signal corresponding to the dissolved oxygen in the medium. A valve mechanism selectively applies air, N.sub.2, O.sub.2 and CO.sub.2 to the medium. A controller produces a control signal for controlling the operation of the valve means so that a substantially fixed volume of gas consisting of one or more of air, CO.sub.2, N.sub.2 and O.sub.2 are added to the fermenting medium during a period of time. The controller determines in response to the dissolved oxygen and pH signals, the amount of CO.sub.2, O.sub.2 and/or N.sub.2 required to effect dissolved oxygen and pH correction. The controller further adjusts these determined values to compensate for the displacement of the CO.sub.