1. Compact structure, small footprint. Submersible sewage pump submersible work, so can be installed directly in the sewage tank, without the need to build a dedicated pump room for the installation of pumps and machines, you can save a lot of land and infrastructure costs. 2 installation and maintenance easy. Small submersible sewage pump can be freely installed, large submersible sewage pumps are generally equipped with automatic coupling device can be automatically installed, installation and maintenance quite convenient. 3. Continuous operation for a long time. Submersible sewage pump due to pump and motor coaxial, short shafts, rotating parts light weight, so the bearing load (radial) is relatively small, longer life expectancy than the average pump. 4. There is no cavitation damage and irrigation water and other issues. Especially after the point to the operator has brought great convenience. 5. Vibration noise, low motor temperature, pollution-free environment. It is because of the above advantages, submersible sewage pump has been more and more people's attention, the use of a more and more wide range from the original purely for the transport of fresh water to the present can transport a variety of domestic sewage, industrial wastewater, construction Site drainage, liquid feed and more. In municipal engineering, industry, hospitals, buildings, restaurants, water conservancy construction plays a very important role in all walks of life. But everything is divided into two parts, the most critical issue for the submersible sewage pump is the problem of reliability, because the submersible sewage pump is used under the liquid occasion; the medium is mixed with some mixed liquid containing solid material ; Pump and motor * are very close; pump is vertical layout, the weight of rotating parts and impeller pressure in the same direction. These problems make the submersible sewage pump in sealing, motor carrying capacity, bearing arrangement and selection requirements than the average sewage pump is higher. In order to improve the life of submersible sewage pump, most domestic and foreign manufacturers are now on the pump protection system think of a way that the pump leaks, overload, over-temperature and other failures can automatically alarm and automatically shut down for repair. However, in our opinion, it is necessary to set up a protection system in the submersible sewage pump, which can effectively protect the safe operation of the electric pump. However, this is not the crux of the problem. The protection system is only a remedy after a pump failure. It is a relatively passive approach. The crux of the problem should be from the very beginning, to completely solve the pump in the sealing, overload and other issues, this is a more proactive approach. To this end, we apply the sub-impeller hydrodynamic sealing technology and the pump's no-overload design technology to the submersible sewage pump, greatly improving the pump seal reliability and carrying capacity and prolonging the service life of the pump. First, the application of the impeller hydrodynamic sealing technology The so-called vice impeller hydrodynamic seal is installed on the back of the pump impeller rear cover near the coaxial reverse direction to install an open impeller. When the pump is working, the auxiliary impeller rotates with the pump main shaft, and the liquid in the auxiliary impeller will also rotate together. The rotating liquid will generate an outward centrifugal force that on the one hand withstands the liquid flowing to the mechanical seal and lowers the mechanical Sealing pressure. On the other hand prevent the solid particles in the medium from entering the friction pair of the mechanical seal, reduce the abrasion of the mechanical seal and prolong the service life of the mechanical seal. In addition to sealing the secondary impeller play a role, but also can play a role in reducing the axial force in the submersible sewage pump axial force is mainly caused by the liquid pressure on the impeller pressure force and the entire rotating part of the composition of gravity, which The direction of action of the two forces is the same, the resultant force is formed by the sum of two forces.