Submersible sewage pump is a kind of pump and motor connected, and at the same time submerged into the liquid pump work, compared with the general horizontal pump or vertical sewage pump, submersible sewage pump has obvious advantages in the following aspects:
1. Compact structure, small footprint. The submersible sewage pump can be directly installed in the sewage pool because it is submerged under the liquid. There is no need to build a special pump room to install the pump and the machine, which can save a lot of land and infrastructure costs.
2. Easy installation and maintenance. Small submersible sewage pumps can be installed freely. Large submersible sewage pumps are generally equipped with automatic coupling devices for automatic installation and installation and maintenance are very convenient.
3. Long running time. Submersible sewage pump Because the pump and the motor are coaxial, the shaft is short, and the rotating parts are light. Therefore, the load (radial) on the bearing is relatively small, and the service life is much longer than that of a general pump.
4. There are no problems such as cavitation damage and flooding. In particular, the latter point brings great convenience to the operators.
5. Small vibration and noise, low motor temperature rise, no pollution to the environment.
Due to the above advantages, submersible sewage pumps have attracted more and more attention from people, and the scope of use has also become wider and wider. From the original purely used to transport clean water to the present, various submersible sewage, industrial wastewater, and construction can be transported. Site drainage, liquid feed, etc.
It plays a very important role in various industries such as municipal engineering, industry, hospitals, architecture, restaurants, and water conservancy construction.
However, everything is divided into two parts. The most critical issue for submersible sewage pumps is the issue of submersible sewage pumps. The submerged sewage pump is used under liquid conditions; the medium to be transported is mixed liquid containing solid materials. The pump and the motor* are in close proximity; the pump is in a vertical arrangement and the weight of the rotating part is in the same direction as the impeller is subjected to the water pressure. These problems make the requirements of the submersible sewage pump in terms of sealing, motor bearing capacity, bearing arrangement and selection, etc. higher than that of a general sewage pump.
In order to improve the life of the submersible sewage pump, most domestic and foreign manufacturers are now thinking of ways to protect the pump system, that is, when the pump leaks, overload, over temperature and other faults 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 sewage pump, which can effectively protect the safe operation of the electric pump.
But this is not the crux of the problem. The protection system is only a remedy after the pump failure. It is a passive method. The key to the problem should be to start from the root and completely solve the problem of the pump in terms of sealing, overload, etc. This is a more proactive approach. For this purpose, we apply the sub-impeller fluid dynamic sealing technology and the pump's no-overload design technology to the submersible sewage pump, greatly improving the pump sealability and load carrying capacity, and extending the pump's service life.
First, the application of the auxiliary impeller hydrodynamic sealing technology The so-called secondary impeller hydrodynamic seal refers to the installation of an open impeller in the opposite direction of the back of the pump impeller rear cover. When the pump is working, the secondary impeller rotates with the pump spindle, and the liquid in the auxiliary impeller also rotates together. The rotating liquid generates an outward centrifugal force that resists the flow of liquid to the mechanical seal on the one hand and reduces the mechanical load. Pressure at the seal. On the other hand, the solid particles in the medium are prevented from entering the mechanically sealed friction pair, which reduces wear of the mechanical seal grinding block and prolongs its service life.
In addition to the sealing function, the auxiliary impeller can also reduce the axial force. In the submersible sewage pump, the axial force is mainly composed of the pressure differential force acting on the impeller and the gravity of the entire rotating part. The direction of the two forces is the same, and the resultant force is the sum of two forces. It can be seen that under the same performance parameters, the axial force of the submersible pump is larger than that of the horizontal pump, and the balance is more difficult than that of the vertical pump. Therefore, in the submersible sewage pump, the reason that the bearing is easily damaged is also related to the large axial force.
If the auxiliary impeller is installed, the direction of the differential pressure force exerted by the liquid on the auxiliary impeller is opposite to the combined force of the above two forces, so that a part of the axial force can be canceled and the bearing life can be extended. However, the use of the auxiliary impeller sealing system also has a disadvantage in that it consumes a part of energy on the auxiliary impeller, which is generally about 3%, but as long as the design is reasonable, it can completely reduce this part of the loss to a minimum.
Second, the application of the pump's non-overload design technology In the general centrifugal pump, the power always increases with the increase of the flow rate, that is, the power curve is a curve that increases with the increase of the flow rate. Use will bring a problem: When the pump is operating at the design operating point, in general, the pump power is less than the motor rated power, the use of this pump is safe; but when the pump head is reduced, the flow will increase ( As can be seen from the performance curve of the pump, the power also increases.
When the flow exceeds the design point flow 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. When the motor is overloaded, either the protection system acts to stop the pump, or the protection system fails to burn the motor.
The head of the pump is lower than the point where the head of the design condition is used. In practice, it is often encountered. In one case, when the pump is selected, the head of the pump is selected too high, and in actual use, the pump is to reduce the head. Used; Another situation is that in the use of the pump operating point is not very good to determine, in other words the pump flow needs to be adjusted often; Another case is that the pump needs to constantly change the location of use. These three conditions may cause the pump to overload and affect the use of the pump. It can be said that for pumps that do not have full head characteristics (including submersible sewage pumps), the range of their use will be limited to a large extent.
The so-called full head characteristic (also called no-overload characteristic) means that the power curve rises very slowly with increasing flow rate. It is more desirable that when the flow rate increases to a certain value, the power will not only rise but will increase. Falling, that is to say the power curve is a hump curve, if so, we only need to select the power rating of the motor slightly beyond the power point of the hump point, then in the entire range of 0 flow to the maximum flow, regardless of the one in the Operating conditions point, the pump power will not exceed the motor power and overload the pump, for this type of performance of the pump, whether it is selected or used, it will be very convenient and reliable. In addition, the motor power does not need to match Too big can save considerable equipment costs.
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