submersible sewage pumpIt is a type of pump product that is connected to a motor and works underwater at the same time. Compared with general horizontal pumps or vertical sewage pumps, submersible sewage pumps have the following advantages:
1. Compact structure and small footprint. Submersible sewage pumps can be directly installed in sewage tanks due to their underwater operation, without the need to build specialized pump rooms for installing pumps and machines, which can save a lot of land and infrastructure costs.
2. Easy installation and maintenance. Small submersible sewage pumps can be freely installed, while large submersible sewage pumps are generally equipped with automatic coupling devices for automatic installation, making installation and maintenance quite convenient.
3. Long continuous operation time. Submersible sewage pumps, due to their coaxial pump and motor, short shaft, and lightweight rotating components, bear relatively small radial loads on their bearings and have a much longer lifespan than regular pumps.
4. There are no issues such as cavitation damage or water injection. Especially the latter point has brought great convenience to the operators.
5. Low vibration noise, low motor temperature rise, and no pollution to the environment.
It is precisely because of the above advantages that submersible sewage pumps have been increasingly valued and used in a wider range, from simply transporting clean water to now being able to transport various types of domestic sewage, industrial wastewater, construction site drainage, liquid feed, and so on.
It plays a very important role in various industries such as municipal engineering, industry, hospitals, construction, restaurants, and water conservancy construction.
But everything is divided into two parts, forsubmersible sewage pumpThe most critical issue is usability, as submersible sewage pumps are used underwater and transport mixed liquids containing solid materials. The pump is located very close to the motor and is arranged vertically. The weight of the rotating components is in the same direction as the water pressure borne by the impeller. These issues make the requirements for sealing, motor bearing capacity, bearing arrangement, and selection of submersible sewage pumps higher than those of general sewage pumps.
to improvesubmersible sewage pumpCurrently, most manufacturers both domestically and internationally are working on pump protection systems that can automatically trigger alarms and shut down for repairs in the event of pump leaks, overloads, overheating, and other malfunctions. But we believe that it is necessary to install a protection system in submersible sewage pumps, which can effectively protect the safe operation of the electric pump.
But this is not the key issue, the protection system is just a remedial measure after a pump failure, which is a relatively passive approach. The key to the problem should be to start from the root and solve the problems of pump sealing, overload, etc. This is a more proactive approach. To this end, we have applied the hydrodynamic sealing technology of the secondary impeller and the overload free design technology of the pump to the submersible sewage pump, greatly improving the pump's sealing and load-bearing capacity, and extending the pump's service life.
1、 Application of hydrodynamic sealing technology for secondary impeller
The so-called secondary impeller fluid dynamic seal refers to the installation of an open impeller in the opposite direction of the same axis near the back cover plate of the pump impeller. When the pump is working, the secondary impeller rotates together with the pump spindle, and the liquid in the secondary impeller also rotates. The rotating liquid generates an outward centrifugal force, which on the one hand resists the liquid flowing towards the mechanical seal and reduces the pressure at the mechanical seal. On the other hand, it prevents solid particles in the medium from entering the friction pair of the mechanical seal, reduces the wear of the mechanical seal grinding block, and extends its service life.
In addition to sealing, the secondary impeller can also reduce axial force. In submersible sewage pumps, axial force is mainly composed of the pressure difference force of the liquid acting on the impeller and the gravity of the entire rotating part. The direction of these two forces is the same, and the resultant force is the sum of the two forces. It can be seen that under the same performance parameters *, the axial force of submersible sewage pumps is greater than that of general horizontal pumps, and the balancing difficulty is more difficult than that of vertical pumps. So in submersible sewage pumps, the reason why bearings are easily damaged is also closely related to the large axial force.
If a secondary impeller is installed, the direction of the pressure difference force exerted by the liquid on the secondary impeller is opposite to the combined force of the two forces, which can offset some of the axial force and prolong the bearing life. However, there is also a disadvantage to using a secondary impeller sealing system, which is that a portion of energy is consumed on the secondary impeller, usually around 3%. However, as long as the design is reasonable, this loss can be reduced to the lowest possible level.
2、 Application of overload free design technology for pumps
In a typical centrifugal pump, the power always increases with the increase of flow rate, that is to say, the power curve is a curve that rises with the increase of flow rate. This poses a problem for the use of the pump: when the pump operates at the design operating point, generally speaking, the power of the pump is less than the rated power of the motor, and the use of this pump is safe; But when the pump head decreases, the flow rate will increase (as can be seen from the pump's performance curve), and the power will also increase accordingly.
When the flow rate exceeds the design operating point and reaches a certain value, the input power of the pump may exceed the rated power of the motor, causing the motor to overload and burn out. When the motor is overloaded, either the protection system will activate to stop the pump from rotating; Either the protection system fails and the motor burns out.
The situation where the pump head is lower than the design operating point head is often encountered in practice. One situation is that when selecting the pump, the pump head is too high, but in actual use, the pump head is reduced; Another situation is that it is difficult to determine the operating point of the pump during use, in other words, the flow rate of the pump needs to be adjusted frequently; There is also a situation where the pump needs to be frequently relocated for use. These three situations may overload the pump and affect its usability. It can be said that for pumps without full head characteristics (includingsubmersible sewage pump）Its scope of use will be greatly limited.
The so-called full head characteristic (also known as overload free characteristic) refers to the very slow rate at which the power curve rises with the increase of flow rate. Ideally, when the flow rate reaches a certain value, the power not only does not rise again, but also decreases. In other words, the power curve is a curve with a hump. If this is the case, as long as we choose a power value slightly above the hump point of the motor rated power, then in the entire range from 0 flow rate to the maximum flow rate, no matter which operating point you operate at, the pump power will not exceed the motor power and cause the pump to overload. For pumps with this performance, both selection and use will be very convenient. In addition, the motor power does not need to be too high, which can save considerable equipment costs.