Self-balancing Multistage Centrifugal Pump VS Balancing Disc Multistage Centrifugal Pump

Do you know about self-balancing? Do you know why is self-balancing better than balance disc? Do you know the advantages of self-balancing? Learn more please review it below.
Multistage Pump (Balance Disc Type)

1. What's Balance Disc Multistage Centrifugal Pump? 


A multistage centrifugal pump is a pump that has two or more impellers. Both balance disc type and self-balance type can absorb water and press water in multiple stages , so that the water can be raised to a high position. However,balance disc type equipped with an extra device called "balance system". In China, we usually call it the "conventional multistage centrifugal pump".


balance disc multistage pump structure


2. Why Do We Call It “Conventional Pump”?


Since the common ones on the market are multistage centrifugal pumps with balancing disc which the structure is outdated, we call them conventional multistage pumps. It has obvious defects in the operation process. See the main defects below:

(1) Balancing disc system is easy to wear and fail
Due to the outdated structure of the conventional multistage pump, the axial force is eliminated by the balancing system (balance disc and balance ring).
Since the clearance between the balance disc and the balance ring is small, the working environment is high, a variety of factors lead to mutual friction, the service life is very short. At the same time, due to the wear of the balance plate and the balance ring, the impeller is moved toward the water inlet end, and the friction between the impeller and the seal ring, the impeller and the middle section is intensified.

With the increase of operating time, the balance effect will gradually decrease, the pump will be intensified, the noise will be high, the efficiency will drop, the flow, head and efficiency will not meet the design requirements, and the shaft power will increase. What is more, the components will be damaged. The rotor is locked, the shaft is broken, the motor is burnt, and the pump cannot work normally until it is dry.

(2) Non-failure operation period is short and the components are easy to wear (including balancing disc, balancing ring, impeller, seal ring, guide vane, shaft sleeve, rotor and so on) and maintenance cost is high.
The working condition is not bad then it can used less than a year. The pump have to be repaired in a few months when in bad working condition. The balancing plate, balancing ring and rotor parts need to replaced constantly. It is even worse if using mechanical seal. excluding labor costs and production loss, the cost of components for each rotor replacement is 40-50% of the equipment purchase cost.

(3) Performance parameters are not up to standard, low efficiency, high shaft power
Since 10-20% of the flow rate of the conventional multistage pump design is used to balance water supply of the system , we call it the equilibrium water return to form a volume leak, the leakage is 10-20% of the rated flow, the small flow high lift pump, the leakage is as high as 20%, the actual water output is only about 85% of the design flow, resulting in low efficiency of the pump, low efficiency will increase the shaft power. Thus resulting in the design of the operating parameters are not up to standard, the efficiency is reduced, the shaft power increases the serious consequences. Since the design flow is not up to standard, the cost of doing work per unit time will increase significantly.

(4) Rotor can not be positioned and service life of mechanical seal (or packing seal ) is short
Because the axial force of the conventional multistage pump can not be completely eliminated, the pump has 3-5mm axial turbulence during operation. When the rotor is working, the rotor will move left and right and cannot be positioned. Because the rotor cannot be positioned, the dynamic ring and static ring will fail to return to the position in time. Dynamic and static rings fail due to poor contact and will result in serious leakage.

(5) Simple structure and small temperature range
As the conventional multistage pump has a simple structure, the uniform symmetry is poor in thermal expansion and contraction, the balance system is unstable, the mechanical seal cannot be positioned, the bearing lubrication method is unreasonable, and the cooling treatment cannot be performed, and the temperature resistance range of the water pump is limited. The temperature can only withstand below 120 °C. If it is a high temperature condition, it will be helpless.

Multistage Pump(Self-balance Type)

1. What's Self-balancing Multistage Centrifugal Pump?


The self-balancing multistage centrifugal pump is a new multistage centrifugal pump that has been innovated and improved on the basis of the conventional multistage pump. It is still two or more impellers, but it is innovative in structure. The impellers are arranged symmetrically, and the water outlet of the pump is located in the middle of the positive and reverse impellers.

self-balance multistage pump structure


2. What Are The Advantages Of Self-balancing Multistage Pump?


(1) The symmetrically impellers make the axial thrust balanced out and no axial movement.

impeller arrangement of self-balance pump
(2) Without balancing disc system, self-balancing multistage pump solves various faults due to failures of balancing device such as balancing plate and ring wearing and locking of rotor parts. Impellers and guide vanes always in their positions under any circumstances, which make longer service life of pump. The safety operation time is more than 3 times of the conventional one.

(3) There is no water return loss due to the self-balancing structure design. The performance parameters is 100% meet the designing requirements, and the efficiency has been raised 4-14%, and shaft power has been reduced. Thus the operation cost has been reduced in an obvious way.

(4) Since there is no axial turbulence, the contact effect of mechanical seal dynamic and static ring is good when the pump starts and stops, which overcomes the defects that the mechanical seal dynamic and static ring of conventional multistage pump can not be return to its position in time , and the mechanical seal life is extended by 2-3 times.


(5) The self-balancing axial force loads minimize the pump wear and system interference. The residual axial force of a very small part is absorbed by the thrust bearing, so that the pump shaft is always in the tension state, and the force of the shaft is even, which Increasing the rigidity and critical speed of the pump rotor, as well as smoothness and reliability of rotor operation.

(6) The structure of the bearing body is changed, and the splash oil bath is used for lubrication. This lubrication method is safe and reliable, the heat dissipation performance is good, the oil level is visible, and it is very easy to add and replace .As long as the oil (or turbine oil) is refilled and replaced as required, there will be no burning of the bearing and the service life of the bearing will be prolonged. (conventional multistage pumps are grease-lubricated, which is volatile, heats up quickly, oil level invisible, and is difficult to add.)

bearing A of self-balance pumpbearing B of self-balance pump
(7) Due to the good positioning of the mechanical seal and the change of the structure of the bearing body, the cooling range of the pump can be increased by 200 °C by add the cooling device. (Conventional one less than 120°C)

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