The most important components of sanitary pumps are impeller, pump casing and shaft sealing device. 1. Impeller-The impeller isthe core partof the sanitary centrifugal pump . The impeller usually has several forms as shown in the figure. The one with cover plates on the front and back is called the closed type; the one without cover plates at the front and the back is called the open type; the one with only the rear cover plate and no front cover is called the semi-open type. Open and semi-open impellers are suitable for conveying suspensions containing solid particles because the flow passages are not easy to block, but the efficiency is low. Generally, centrifugal pumps use enclosed impellers, which are highly efficient and suitable for transporting clean liquids. The centrifugal sanitary negative pressure pump referred to in the food industryoften adopts a closed impeller with fewer blades due to the requirements of sanitation and frequent cleaning. Second, the pump casing-the pump casing of the centrifugal pump is an energy conversion device. After the impeller is installed in the pump casing, a volute-shaped passage with a gradually enlarged cross-section is formed. Therefore, the kinetic energy of the high-speed liquid flow thrown around the impeller can be gradually converted into static pressure energy. In order to reduce the energy loss caused by collision when the fluid directly enters the volute, some centrifugal pumps are equipped with a fixed guide wheel between the impeller and the pump casing. The guide wheel has many gradual turning flow passages, and the gentle fluid directly enters the pump casing. The effect of, reduces the energy loss caused by the collision of the fluid, and makes the conversion from kinetic energy to static pressure energy more effective.