Advantages, disadvantages and usage of submersible pump

Submersible pump is a kind of pump product which is connected with the motor and works under the liquid at the same time. It has obvious advantages in the following aspects:

1. Compact structure and small floor space. Since the submersible sewage pump works under the subsurface of the fluid, it can be directly installed in the sewage tank without the need to build a special pump house to install pumps and machines, which can save a lot of land and infrastructure costs.

2. Easy installation and maintenance. Small submersible sewage pump can be installed freely, while large submersible sewage pump is usually equipped with automatic coupling device for automatic installation, installation and maintenance is quite convenient.

3. Long continuous operation time. Submersible sewage pump due to pump and motor coaxial, short shaft, rotating parts of light weight, so the bearing load (radial) is relatively small, the life is much longer than the general pump.

4. There are no cavitation damage and irrigation and water diversion problems. In particular, the latter point has brought great convenience to the operator.

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

It is because of the above advantages, the diving sewage pump has been more and more attention, the scope of use is more and more wide, from the original simply used to transport clean water to now can transport a variety of domestic sewage, industrial wastewater, construction site drainage, liquid feed, and so on.

Submersible pump

In municipal engineering, industry, hospital, construction, hotel, water conservancy construction and other industries play a very important role.

But everything has two sides, and the key issue for the submersible sewage pump is its accessibility, because the submersible sewage pump is used under liquid; The medium is some mixed liquid containing solid materials; The pump is very close to the motor *; The pump is vertically arranged, the weight of the rotating part and the impeller bear the same direction of water pressure. These problems make the diving sewage pump in the sealing, motor bearing capacity, bearing arrangement and selection requirements than the general sewage pump.

In order to improve the life of submersible sewage pump, most manufacturers at home and abroad are now trying to find a way on the protection system of the pump, that is, when the pump leakage, overload, overtemperature and other faults can be automatically alarm, and automatically shut down for repair. However, we believe that it is necessary to set up the protection system in the diving sewage pump, which can effectively protect the safe operation of the electric pump.

But this is not the key to the problem, protection system is only in the pump failure after a remedy, is a more passive way. The key to the problem should be from the root, completely solve the pump in the sealing, overload and other aspects of the problem, this is a more active way. Therefore, we apply the hydraulic seal technology of the auxiliary impeller and the non-overload design technology of the pump to the submersible sewage pump, which greatly improves the sealing ability and bearing capacity of the pump, and extends the service life of the pump.

Application of hydrodynamic seal technology of secondary impeller

The so-called secondary impeller hydrodynamic seal refers to the pump impeller back cover plate near the coaxial opposite direction of the installation of a type of impeller. When the pump works, the secondary impeller with the pump spindle rotation, the liquid in the secondary impeller will rotate together, rotating liquid will produce an outward centrifugal force, the centrifugal force on the one hand against the flow of mechanical seal in the liquid, reduce the pressure of the mechanical seal. On the other hand, it prevents the solid particles in the medium from entering the friction pair of the mechanical seal, reduces the wear of the grinding block of the mechanical seal, and extends 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 sewage pump, the axial force is mainly composed of the pressure difference force of liquid acting on the impeller and the gravity of the whole rotating part. The direction of action of the two forces is the same, and the resultant force is formed by the addition of the two forces.

It can be seen that when the performance parameters are exactly the same, the axial force of submersible sewage pump is larger than that of general horizontal pump, and the balance difficulty is more difficult than that of vertical pump. Therefore, in the submersible sewage pump, the bearing is easy to damage and the reason is also a great relationship with the axial force.

And if the secondary impeller is installed, the direction of the liquid acting on the secondary impeller is opposite to the resultant force of the above two forces, which can offset part of the axial force, and thus play a role in extending the bearing life. But the use of secondary impeller sealing system also has a disadvantage, that is, in the secondary impeller to consume part of the energy, generally about 3%, but as long as the design is reasonable, can reduce this part of the loss to the minimum

Application of pump design technology without overload

In general centrifugal pump, the power is always along with the increase with the increase of the flow, that is to say, the power curve is a rising curve with the increase of flow rate, the use of the pump will lead to a problem: when the pump design point operation, in general, the power is less than the motor rated power of the pump, the use of the pump is safe; However, when the pump head decreases, the flow rate increases (as can be seen from the performance curve of the pump) and the power increases accordingly.

When the flow exceeds the flow at the design working condition and reaches a certain value, the input power of the pump may exceed the rated power of the motor and cause the motor overload and burn. When the motor is overloaded, it can either protect the system to stop the pump from rotating; Or the protection system fails and the motor burns down.

The pump head is lower than the design working condition of the use of the head, is often encountered in practice, one is in the pump selection, the pump head is too high, and the actual use of the pump is to reduce the head; Another case is that the operating point of the pump in use is not easy to determine, in other words, the flow of the pump needs to be adjusted often; There is also a case where the pump needs to be used in different locations. These three conditions may overload the pump and affect pump availability. It can be said that for pumps without full head characteristics (including submersible blowdown pumps), the range of use will be largely limited.

So-called total head features (also known as no overload characteristics) refers to the power curve rise with the increase of flow speed is very slow, is more ideal when the flow increased to a certain value, the power not only won't rise, it will declined, that is to say, the curve of the power curve is a hump, if so, we just choose the motor rated power point slightly over the hump of power value, so at zero flow to the largest flow of the whole range, whatever you run on that one point, the power will be no more than a motor power of the pump and make the pump overload, to have the performance of the pump, selection and use, Will be very convenient and * *. In addition, the motor power does not need to be too large, which can save considerable equipment costs.