The submersible drainage pump is a kind of pump product that works submerged in the liquid while the pump and motor are connected. Compared with the general horizontal pump or vertical sewage pump, the submersible drainage pump obviously has the following advantages:

1. compact structure, small footprint. submersible drainage pump can be installed directly in the cesspool because it works under the liquid, so there is no need to build a special pump room to install the pump and machine, which can save a lot of land and infrastructure costs.

2. Easy installation and maintenance. Small submersible drainage pumps can be installed freely, and large submersible drainage pumps are generally equipped with automatic coupling devices for automatic installation, making installation and maintenance quite convenient.

3.Long continuous running time. submersible drainage pump has a shorter shaft and lighter weight rotating parts due to the coaxial pump and motor, so the radial load on the bearing is relatively small and the life span is much longer than normal pumps.

4. There is no cavitation damage and irrigation and diversion of water and other problems. Especially the latter point brings great convenience to the operator.

5. Small vibration noise, low motor temperature rise, no pollution to the environment.

Because of the above advantages, the submersible drainage pump has become more and more important to people, and the scope of use has become more and more extensive, from the original simply used to transport clear water to the current can transport a variety of domestic sewage, industrial wastewater, construction site drainage, liquid feed, etc..

In municipal projects, industry, hospitals, construction, hotels, water conservancy construction and other industries play a very important role.

But everything is divided into two, for submersible drainage pump, the most critical issue is reliability, because the use of submersible drainage pump is under the liquid; the medium is some mixed liquid containing solid materials; the pump and the motor are close to each other; the pump is arranged vertically, the rotating parts The weight of the pump is the same as the impeller bearing water pressure. These problems make the submersible drainage pump in the seal, motor load capacity, bearing arrangement and the choice of the requirements than the general sewage pump is higher.

In order to improve the life of the submersible drainage pump, most manufacturers are now thinking about the pump protection system, that is, in the event of leakage, overload, over temperature and other failures in the pump can be automatically alarmed, and automatically shut down for repair. However, we believe that it is necessary to set up a protection system in the submersible drainage pump, which can effectively protect the safe operation of the electric pump. But this is not the key to the problem, the protection system is only a remedy after the failure of the pump, is a more passive approach. The key to the problem should be to start from the root, to completely solve the pump in the seal, overload and other aspects of the problem, which is a more active approach. To this end, we have applied the technology of hydrodynamic sealing of the vice impeller and the design technology of the pump without overload to the submersible sewage pump, which has greatly improved the reliability of the pump seal and bearing capacity, and extended the service life of the pump.

1. Application of sub impeller hydrodynamic sealing technology

The so-called vice impeller hydrodynamic seal is the back of the impeller in the pump near the back of the cover plate coaxially installed in the opposite direction of an open impeller. When the pump works, the sub impeller rotates with the pump main shaft, and the liquid in the sub impeller will also rotate together, and the rotating liquid will generate an outward centrifugal force, which on the one hand tops the liquid flowing to the mechanical seal and reduces the pressure at the mechanical seal. On the other hand, the solid particles in the medium are prevented from entering the frictional side of the mechanical seal, which reduces the wear of the mechanical seal and prolongs its service life.

In addition to playing a sealing role, the secondary impeller can also play a role in reducing the axial force. In the submersible drainage pump, the axial force is mainly composed of the differential pressure of the liquid acting on the impeller and the gravity of the entire rotating part, the direction of action of these two forces is the same, and the combined force is made up of two forces added together. It can be seen that in the case of identical performance parameters, the axial force of submersible drainage pump is larger than that of general horizontal pumps, and the balance difficulty is more difficult than that of vertical pumps. So in the submersible drainage pump, the bearing is easy to damage the reason is also has a great relationship with the large axial force.

And if the installation of the vice impeller, the liquid acting on the vice impeller differential pressure force direction is the opposite of the above two forces, which can offset part of the axial force, also played a role in extending the life of the bearing. However, the use of sub-impeller sealing system also has a disadvantage, that is, in the sub-impeller to consume part of the energy, generally in about 3%, but as long as the design is reasonable, can completely reduce this part of the loss to a minimum.

2. The application of pump design technology without overload

In the general centrifugal pump, power always increases with the flow, that is, the power curve is a curve that increases with the flow, which will bring a problem to the use of the pump: when the pump in the design operating point, generally speaking, the power of the pump is less than the rated power of the motor, the use of this pump is safe; but when the pump head is reduced, the flow will increase from the pump performance curve can seen, the power also increases.

When the flow rate exceeds the design working point flow rate and reaches a certain value, the input power of the pump may exceed the rated power of the motor and cause the motor to overload and burn up. When the motor is overloaded, either the protection system will stop the pump; or the protection system will fail and the motor will burn up.

Pump head is lower than the design working point head use, in practice is also often encountered, a situation is in the pump selection, the pump head selected too high, and the actual use of the pump is to reduce the head use; another situation is that in the use of the pump working point is not very well determined, in other words, the pump flow needs to be adjusted frequently; another situation is that the pump needs to change the location often. These three cases may make the pump overload and affect the reliability of the use of the pump. So to speak, for no full head characteristics of the pump, including submersible sewage pumps, its use will be largely limited.

The so-called full head characteristics also known as no overload characteristics refers to the power curve with the flow increases and the rate of rise is very slow, more desirable is when the flow increases to a certain value, the power will not only rise again, but will decline, that is, the power curve is a curve with a hump, if so, we just choose the motor rated power slightly more than the power value of the hump point, then in the 0 flow to the maximum Flow rate of the entire range, you no matter in that a working point of operation, the pump power will not exceed the motor power.