The working principle of the balance disc of a multi-stage centrifugal pump and the method and steps for adjusting the gap

 

Working Principle of the Balance Plate in a Multi-stage Centrifugal Pump:

The impellers of a multistage centrifugal pump are all arranged in the same direction, and the axial forces on each stage are in the same direction. To balance the axial forces, a balancing mechanism is designed to ensure this balance. The balancing disc assembly consists of a balancing disc, a balancing sleeve, and a balancing seat.

 

The axial force of a multi-stage, segmented centrifugal pump is balanced by a balance plate on the high-pressure side. The balancing principle utilizes the pressure differential across the plate to balance the impeller's axial thrust. Since the axial thrust varies with operating conditions, the balancing force must also vary accordingly. Specifically, the pressure differential across the plate multiplied by the plate's area must always equal the axial force.

Since the water pressure flowing to the balance plate is the same as the water pressure of the final-stage impeller, if the axial force F exceeds the balancing force A, the rotor shaft will tilt leftward toward the low-pressure side of the fountain. However, the balance plate, fixed to the rotor shaft, will only reduce the axial clearance b, increasing flow resistance. This will increase the pressure on the left side of the balance plate, increasing the balancing force A acting on the plate. This will tilt the rotor shaft rightward toward the high-pressure side of the fountain, further increasing clearance b. This is the principle of the balance plate's automatic balancing. However, due to the inertia of the shaft displacement, the rightward push position will not return to the original leftward push position, nor will it immediately stop at the new equilibrium position. Instead, it will overshoot the original position. At this point, the axial clearance (b) is too large, causing the balancing force to be smaller than the axial force, so the rotating shaft will shift to the left again. Due to inertia, the leftward shift will be too much, causing the balancing force to be greater than the axial force. This back-and-forth movement generates low-frequency vibration. At the same time, the thrust pad will heat up and burn out when the axial force is too large. If the axial force continues to increase, the contact surface of the dynamic and static parts of the balance plate will wear during the friction process. Over time, the dynamic and static plates will seize, causing vibration, which seriously threatens the safe operation of the pump.

 

Adjustment method and steps of the balance plate gap of a multistage pump:

 

During multistage pump operation, improper adjustment of the balance plate clearance can easily lead to shaft movement, excessive vibration, and even component wear. Many technicians find this adjustment arduous, but it's actually quite simple if you master the correct method and follow the steps. Below, multistage pump manufacturer HNYBPUMP will explain in detail the methods and steps for adjusting the balance plate clearance of multistage pumps. Following these steps can help you avoid many mistakes.

 

• Step 1: Prepare for Adjustment

First, stop the pump and disconnect the power supply. After ensuring safety, disassemble the pump casing to expose the rotor assembly.

Gather the necessary tools, including a feeler gauge (common gauge: 0.02-1mm), a dial indicator, and a wrench.

Cleanse any oil and rust from the balancing disc and balance ring. Any signs of wear must be removed immediately, otherwise the clearance measurement will be inaccurate.

 

• Step 2: Measure the Current Clearance

Push the rotor toward the suction port so that the balancing disc and balancing ring fit tightly together.
Insert a feeler gauge between the balancing disc and balancing ring and measure. To ensure data accuracy, perform multiple measurements and average the results. This average is the actual initial clearance.

The standard clearance for multistage pumps is generally between 0.15mm and 0.3mm. The specific value depends on the pump model and should not be based solely on experience.

 

• Step 3: Precisely Adjust the Clearance

If the measured initial clearance is too small, loosen the locknut on the shaft sleeve and slightly rotate the balancing disc away from the balancing ring.

If the initial clearance is too large, rotate the balancing disc in the opposite direction.

After each adjustment, remeasure the clearance with a feeler gauge until the value meets the standard.

Note: The threads of the balancing disc can easily slip. Apply even force when turning, and avoid using brute force.

 

• Step 4: Recheck, Repair, and Prevent Loosening

After adjusting the clearance, use a dial indicator to check the rotor shaft runout to ensure it is within the allowable range.

Tighten the locknut and remeasure the clearance to prevent any deviation from the previous adjustment.

Finally, reinstall the pump casing and start the pump for a test run. Check whether the operating sound is stable and the vibration is reduced. If everything is normal, the adjustment is complete.

 

The key to adjusting the balancing plate clearance is "slow" and "accurate." Rushing for quick results can easily lead to errors. If you are unsure of your operation, consult the pump's manual or seek assistance from an experienced technician. During daily operation, pay close attention to the pump's operating status. If any abnormalities are detected, promptly checking the clearance can prevent many problems.