Abstract
Since almost all commercially provided dry pumps are of the positive displacement type, the leak flow through clearance between displacement chambers in the pump is a dominant factor which determines pumping performance. Prediction methods for the pumping performance of dry pumps are explained by comparing it to the scroll pump and the screw pump. The scroll pump has long clearances, but the screw pump has relatively short ones, and the volume of the chambers reduces from the inlet toward the outlet in the scroll pump, but that in the screw pump is kept constant throughout the pumping process. Such a structural difference produces a small difference in the way of treating leak flow. These two methods can be applied to the other dry pumps requiring only minor modification.
