After the condensate pump is started, the pump shaft of condensate pump drives the impeller to rotate in high speed together, compelling the liquid filled in vane in advance to rotate. Under the function of inertial centrifugal force, the liquid carries out radial movement from the center of impeller to periphery. During the movement process flowing through impeller, the liquid gets energy, its static pressure increases, and flowing speed increases too. After the liquid leaves impeller and enters into pump case, because the flowing channel inside shell increases gradually and slows down, part of its kinetic energy is transformed into static energy, and finally it flows to drainage pipeline along tangential direction.

Therefore, the snail–shaped pump shell is not only the component to collect the liquid flowing from impeller, but also an energy transformation device. At the same time when the liquid is thrown from impeller centre to periphery, the impeller centre forms a low-voltage zone. And under the function of total potential energy difference between liquid level of storage tank and impeller centre, the liquid is absorbed into the centre of impeller. Depending on the unceasing operation of impeller, the liquid is absorbed and drained continuously. The mechanical energy obtained by liquid in centrifugal pump is finally displayed as the increase of depressurization energy. 

The first grade of shell is calathiform shell or spiral shell, the secondary and the last shell are calathiform shells; the pump shaft is equipped with radial direction bearing at many places. The pump rotor axial direction load can be supported by the thrust bearing of pump itself, and can be supported by the motor; the shaft seal can be packing seal or mechanical seal. The pump rotor shafting system includes two shafts. The connection between shafts is snap ring cylinder type of coupler. The connection between pump and motor is elastic pin coupler or rigid coupler connection; the suction and outlet(disgorging) interface are located in pump cylinder and outlet base respectively, and are laid in 180° horizontally.