The phenomena of a wet vacuum pump are very complicated because liquid and gas exist together affecting each other in the interior of the pump. Theories on a fluid machinery which deals with only liquid or gas can not be applied to a wet vacuum pump. Therefore any theoretical analysis to be satisfied has not been established yet.
Furthermore, in the experiments on a wet vacuum pump, it has been generally accepted that it is not easy to grasp the precise characteristics owing to the scattering of the measured values, and few experimental data have been published, The reason could be as follows : The characteristics of a wet vacuum pump are affected by so many factors in addition to the scale effects of the pump (e.g. gas flow rate, degree of vacuum, compression ratio, piston water and its supply water, etc.). Since these factors have the complicated interaction, it seems to be quite difficult to keep the experiments under control and arrange the measured values.
One of the authors has designed an accurate controlling system of the piston water for the sake of obtaining the exact and stable characteristic curves, and has already reported the experimental results on the wet vacuum pump with Nash type casing (i.e. double suction and exhaust type).
Subsequently, this paper is concerned with the experimental studies on the wet vacuum pump with Elmo type casing (i.e. single suction and exhaust type) and deals chiefly with the effects of the eccentricity of its casing and the flow state of piston water in the interior of the pump.