The pump inside the tank works on the fluid medium through the impeller, which can be commonly referred to as turbomachinery along with mechanical devices such as fans and centrifugal compressors. Usually composed of impellers, shafts, volutes, and sealing mechanisms. When it works, the shaft and impeller are driven by the prime mover to rotate, and the fluid medium moves in a circular motion with the impeller rotation. Under the action of centrifugal force, it is thrown out from the center of the impeller and obtains pressure energy and velocity energy from the impeller. The fluid medium converts some velocity energy into static pressure energy in stationary components such as volutes (or diffusers). In addition, as the fluid is ejected from the center of the impeller, a low-pressure zone is formed at the center of the impeller, creating a pressure difference with the fluid inlet, ensuring that the fluid can be continuously drawn in and discharged at a certain pressure and velocity.
(1) Impeller
The impeller is a component that transfers the energy of the prime mover to the fluid medium. Typically, the impeller consists of a front cover plate, a rear cover plate, blades, and a hub. If there is no front cover plate, it becomes a semi open impeller, and if there are no front and rear cover plates, it is called a starting impeller. If there are both front and rear cover plates, the impeller becomes a closed impeller. In addition, according to whether the bending direction of the blades is the same as the rotation direction of the impeller, it can be divided into forward impellers (which can obtain a larger pressure ratio), backward impellers (which can obtain a larger static pressure energy), and radial impellers (which can obtain a flatter head curve under the condition of sacrificing efficiency).
(2) Pump body inside the tank
The pump body inside the tank usually includes a suction section, a middle section, and a discharge section, which require a certain strength and sealing. To ensure that it does not deform during operation, a certain stiffness is required. The pump body inside the tank is composed of many parts, so it is necessary to ensure the concentricity and perpendicularity of the contact surfaces of each part during installation.
The pump casing inside the tank can be divided into two types: axial and radial. The casing of single-stage tank pumps is volute, while the radial casing of multi-stage tank pumps is generally annular or circular. The inner cavity of the pump casing in the snail shell type tank is designed with a spiral liquid channel to collect the liquid thrown out from the impeller and guide it to the diffusion pipe to the pump outlet inside the tank. The snail shell bears all the working pressure and thermal load of the liquid.
(3) Sealing ring
The function of the sealing ring is to prevent internal and external leakage of the pump inside the tank. The sealing ring is made of wear-resistant material and is embedded on the front and rear cover plates of the impeller and the pump casing inside the tank. It can be replaced after wear.
(4) Shaft and bearings
One end of the pump shaft inside the tank is fixed with an impeller, and the other end is installed with a coupling. According to the size of the pump inside the tank, rolling bearings and sliding bearings can be selected as bearings.
(5) Shaft seal
There are generally two types of shaft seals: mechanical seals and packing seals. Generally, in tank pumps are designed to accommodate both packing seals and mechanical seal structures.
