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Small dry vacuum pumps are emerging in applications for which pumping of condensable gases is necessary. Recent development has permitted a significant increase in condensable pumping capacity. Relevant applications typically include freeze drying, vacuum drying, evaporation, filling of liquid circuit, organic layer coating.
Ability to pump such gases, without using condensers, is not yet well documented with small dry pumps. This paper shows what to change with our habits when using oil free pumps. For a long time, Pneurop method was the standard reference to grasp vapour pumping ability and to compare pumps performances. Applied to dry pumps, this method shows its limitations and requires to be adapted.
Then, this paper includes a theoretical study of gas condensation inside the pump. This study is based on gas thermodynamic properties, pressure and thermal behavior of the pump and gas dilution with an inert permanent gas purge. To illustrate this purpose, our study is mainly focused on multiroots dry vacuum pumps.
An experiment dedicated to water vapour pumping has been set up in our application laboratory and is described in this document. Experimental results are compared to previous theoretical calculation and discussed.
In conclusion of this paper, primary vacuum pumps capability to evacuate condensable gases are summarized and general recommendations are also listed.
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