Analysis on Application of Sewage Pump (2)

First, deputy impeller hydrodynamic seal technology application

 

The so-called sub-impeller hydrodynamic seal is in the pump impeller back cover near the back of the coaxial installation of an open impeller. When the pump work, vice impeller with the pump spindle rotation, vice impeller in the liquid will rotate together, turning the liquid will produce an outward centrifugal force, the centrifugal force on the one hand to withstand the flow of mechanical seal liquid, reducing the mechanical Seal the pressure. On the other hand to prevent the solid particles in the media into the friction of the mechanical seal, reducing the wear of mechanical seal grinding block and prolong its service life.

 

Vice impeller in addition to play a role in sealing, but also can play a role in reducing the axial force in the submersible pump axial force mainly by the role of the liquid in the impeller pressure on the pressure and the entire rotating part of the composition of gravity, which The two forces act in the same direction, and the resultant force is the sum of the two forces. It can be seen that the performance of the same parameters in the case of submersible sewage pump axial force than the general horizontal pump to large, and the balance of difficulty is more difficult than the vertical pump. Therefore, submersible sewage pump, the bearing is easy to damage the reason is also the axial force has a great relationship.

 

If the auxiliary impeller is installed, the direction of the differential pressure acting on the auxiliary impeller is opposite to that of the above two forces, which can cancel out part of the axial force, which will prolong the life of the bearing. However, the use of vice impeller sealing system also has a drawback, that is, vice impeller to consume part of the energy, generally about 3%, but as long as the design is reasonable, can this part of the loss is reduced to a minimum.

 

Second, the pump design technology without overload application

 

In general centrifugal pumps, the power is always increased with the increase in flow, that is, the power curve is a curve with the increase in flow, which the use of the pump will bring a problem: When the pump in the In general, the pump power is less than the rated power of the motor. This pump is safe to use; however, when the pump head is lowered, the flow rate increases (as can be seen from the pump performance curve) Power also increased.

 

When the flow rate exceeds the design point of flow and reach a certain value, the pump's input power may exceed the motor rated power and cause the motor overload and burned. When the motor is overloaded, either the protection system operates to stop the pump, or the protection system fails to burn the motor.

 

Pump head below the design point of use of working conditions, is also often encountered in practice, one case is pump selection, the pump head selected too high, while the actual use of the pump is to reduce the head Use; the other is the pump operating point in use is not very good to determine, in other words the pump flow rate often need to be adjusted; there is a situation where the pump needs to change the location of frequent use. These three conditions may overload the pump and affect pump reliability. It can be said, the pump does not have full-lift characteristics (including sewage pump), its use will be subject to a large extent.

 

The so-called full-lift characteristics (also known as no overload feature) refers to the power curve increases with the flow rate is very slow increase, it is more desirable when the flow increases to a certain value, the power will not only increase, The power curve is a hump curve, if so, as long as we select the motor rated power slightly more than the hump point of the power value, then the flow of 0 to the maximum flow of the entire range, whether you are in that one Operating point on the run, the pump power will not exceed the motor power leaving the pump overload, with this performance of the pump, whether the selection or use, will be very convenient and reliable. In addition the motor power does not need to be too large, can save considerable equipment costs.