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  • David Mitchell

Importance of Setting Impeller Clearances for Vertical Turbines



The Critical Role of VIT Pumps


The correct start-up of Vertical Industrial Turbine (VIT) pumps is crucial, specifically the setting of impeller clearances. Improperly set impeller clearances will lead to catastrophic failures within a short time. Catastrophic failures are immensely expensive to the end-user or installing contractor. In this blog, we will highlight critical points of the start-up process. However, it is best to refer to the manufacturer’s Instruction & Operations Manual (IOM) or consult your local pump specialist.


Estabrook Corporation is a leading regional sales and service organization that distributes high-quality pumps, valves, seals, controls, and repair for a total system solution approach. As a pump specialist in Ohio and upstate New York, we can help you properly set impeller clearances at start-up to get the VIT pumps running correctly from the start.


In the modern marketplace, VIT pumps have the utmost importance and value. VIT pumps move fluids from pits, collection areas, ponds, lakes, rivers, or any application requiring lifted fluids. Many applications use these pumps within industrial processes. Chillers, sumps, cooling towers, and stormwater are just a few applications. These applications (and many more) are critical to the day-to-day operations found across all industrial markets.



Figure 1: The make-up of the Vertical Industrial Turbine




The Consequences of Improperly Set Impellers


The below images provide an example of damage when impellers do not have the proper configurations. In the following pictures, an open impeller design had its clearance set at 0.015-inch. However, the setting should have been 0.130-inch for an enclosed impeller design. Due to this improper configuration, the pump locked up and would no longer rotate. Extensive damage occurred to the bowls, bearings, shafts, and stuffing box. This incorrect setting resulted in a costly repair.




Photos 1 and 2: Suction Bowl Bearing


The bearing at the suction bowl froze and would no longer perform its function. The purpose of suction bowl bearings is to prevent damage by force against a part that supports rotation—in this case, the suction bowl. Once bearings fail, the suction bowl will no longer rotate, which is a big problem for a pump.




Photos 3 and 4: Top Bowl Bearing


The bearing at the top bowl also froze to the shaft, inhibiting the shaft from rotating properly. The bearing needed split in half to remove it from the top bowl. The bearing, however, only comprised a small portion of the damage. The shaft's extensive damage warranted a new shaft to get the pump to rotate properly.




Photos 5 and 6: Additional Damage to the Top Bowl


Another bearing failed in the top bowl. This failure caused the bore area of the bowl to spin, causing damage to the bowl itself. The vanes in the bowl around the bore were cracked and needed replacing.




Photos 7 and 8: Second Impeller Ring


The second impeller ring rubbed on the face of the intermediate bowl. This galled the impeller ring and bowl ring area. Both rings sustained extensive damage and needed replacing.




Photos 9 and 10: Rubber Spider Bearing


The purpose of the spider bearing is to provide additional support and alignment of the shaft. In this case, as bearings failed and force was still applied to rotate the shaft, the pump shaft became further out of alignment. Once this occurs, wear at the spider bearing can be seen.




Photos 11 and 12: Stuffing Box Bearing and Bottom Shaft


The stuffing box bearing was damaged and needed replacing. The bottom shaft sustained visible wear and needed replacing in its entirety.


As one can see, once failure starts to occur in one area, the damage will continue throughout the entire pump since it is all interconnected. Due to the incorrect impeller clearance, the rotating force put tremendous stress throughout the pump. Once the impeller seizes, the bearing starts to fail, which then leads to misalignment. All wearable parts quickly wear, and the damage goes to mechanical parts of the pump, making the failure catastrophic. The impellers and stuffing box become cracked and damaged. The bearings fail, misalignment occurs, and the shaft becomes damaged. All of this is preventable with proper start-up assistance regarding the setting of the impeller clearances.





Critical Information Needed to Set Correct Impeller Clearance


The most critical element of information to know is if the impeller is open or enclosed. Next, you would need to know if the impeller contains a hollow shaft or solid shaft motor, as this will impact the way you set the clearances.


Enclosed impeller designs are more common in the industry. An open impeller requires a much tighter clearance, typically 0.015-inch for the first ten feet of the column length, and 0.010-inch clearance for every additional 10 feet of column length. An enclosed impeller requires a larger clearance, commonly 0.130-inch to 0.188-inch, or larger. To find the exact clearance requirement, one must reference the drawing provided by the manufacture. The drawing may not exist with the IOM, which is why it is beneficial to consult your local pump specialist.



Figure 2: A typical Vertical Turbine Pump performance datasheet


With hollow shaft motors, one can adjust the nut on top of the impeller's motor by moving the nut in a counter-clockwise direction. This lifts the shaft until the impellers clear the seat and the shaft or motor turns freely by hand. Solid shaft motors adjust using a plate located at the coupling of the pump head shaft and motor driveshaft.


If the pump has a thrust pot, do not adjust the impeller position until the installation of the thrust pot. One can adjust the impeller position by using the adjusting nut on the thrust pot. Knowing if you have a solid shaft or hollow shaft motor will be critical as you look to make the impeller adjustment to get it to its correct clearance.





The Benefits of Start-Up Assistance


Referring to the IOM or consulting your local pump specialist for start-up assistance is highly recommended. Vertical Industrial Turbines are excellent pump solutions that can last a long time. These pumps often move a lot of fluid and therefore are commonly large and a significant financial investment. It makes sense to engage your local pump specialist to assist. Estabrook Corporation has over 55 years of experience with pump repair and start-up.





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