Abstract
The capillary viscometer by discharging time is one of the commonly used viscometer. However, the measuring principle of the viscometer of this type is not yet established theoretically, especially the mean effective head of the viscometer is customarilly assumed to be independent on viscosity without theoretical verification.
In this paper, considering some simplified models, it is proved theoretically that the mean effective head of a capillary viscometer depend on viscosity with exception of long enough capillary tube, even when the inlet correction of the capillary tube is assumed constant.
