CIRCULATION PUMP FOR HIGH-PURITY GASES AT HIGH-PRESSURES AND A NOVEL LINEAR MOTOR POSITIONING SYSTEM

A clearance-sealed piston pump has been developed which can be used to move high pressure gases in a closed loop for the purpose of purifica tion, mixing, or phase equilibration. It has been designed primarily w ith the former role in mind, so that inert gases may be used in the pr eparation of high purity intermetallic compounds to suppress the evapo ration of volatile constituents without introducing contamination. To this end, the device is made in such a way as to minimize outgassing, leakage, the formation of dead volumes, and the creation of debris. Th e Dump is intended for use at pressures of up to 200 bar. Its structur al materials are highly resistant to corrosion, and this should enable the device to be used with a wide variety of reactive gases, Flow rat es of between 4.3 and 0.043 / min(-1) can be sustained without difficu lty using realistic loads, although larger and smaller ones are possib le. The pump is capable of producing a head of 0.23 bar. A novel syste m has been developed for sensing and controlling the position of the p iston. This makes it possible to monitor and var?, the instantaneous f low rate while minimizing wear and vibration. The arrangement does not require the presence of a transducer or any kind of feedthrough in th e dean, high pressure environment. It may find applications in other a reas where positioning is needed under hostile or demanding conditions , such as inside ultrahigh vacuum apparatus. (C) 1996 American Institu te of Physics.