Axial thrust and its impact on wear
The reliability of centrifugal pumps depends decisively on the wear of the fixed bearing. In particular, the axial load on the fixed bearing due to the hydraulically generated axial thrust determines the service life of the bearing. With our patented axial thrust measurement, you can determine the axial forces during operation of the pump. You can plan and optimise service intervals and adjust the operating point of the pump so that it has the longest possible running time until the next necessary repair.
Axial thrust is the resulting axial force, which is mainly caused by the pressure difference at the impeller and is supported via the shaft on the fixed bearings.The residual axial thrust is a quality feature of pumps and is checked in particular for multistage centrifugal pumps during the “factory acceptance test”.The residual axial thrust significantly determines the bearing service life.Changes in the axial thrust during operation indicate a changed operating point.
Absorption of the axial thrust through fixed bearings
Centrifugal pumps use centrifugal force to pump liquid. These pumps have one or more impellers (purple), a bearing for radial support (green) and an angular contact ball bearing (orange) to absorb the axial forces from the impeller. The front bearing (green), which only absorbs radial forces, is usually designed as a cylindrical roller bearing, deep groove ball bearing (non-locating bearing) or as a plain bearing.
The axial thrust is absorbed by the rear bearing arrangement (locating bearing in orange). The locating bearing is designed either as a deep groove ball bearing, as a double row angular contact ball bearing or as two angular contact ball bearings in an O or X arrangement. Angular contact ball bearings to absorb the high forces that can arise in the process. Double-row, because axial thrust reversal can also occur.
Centrifugal pump in section; purple: impeller; green: cylindrical roller bearing; orange: double row angular contact ball bearing
Axial thrust compensation and residual axial thrust
The axial thrust can be reduced by a back-to-back design of the impellers in multistage pumps. In this case, the impellers are distributed symmetrically to the suction nozzle so that half of the impellers generate thrust in one direction and the other half in the opposite direction. In single-stage pumps, the axial thrust is reduced either by balancing holes in the impeller or back vanes, so that a good compromise between hydraulic efficiency and bearing life is achieved.
The solution for determining the axial thrust with BestSens
We use the exact knowledge of the bearing geometry and our BestSens SAW technology to determine the influence of the axial thrust on the bearing kinematics.
This allows you to measure the axial thrust of your hydraulics with the original bearing pedestal. For this purpose, the BeMoS L8 sensors are mounted in the bearing pedestal via compression fittings and connected to the BeMoS one controller. With our axial thrust calibration device, we calibrate your bearing pedestal design for a specific force and speed range. You can then measure your hydraulics. Measuring the axial thrust with BestSens technology works for both centrifugal pumps and positive displacement pumps that use angular contact ball bearings or deep groove ball bearings as fixed bearings.
Performed example calibration
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Picture: Motor and bearing bracket of a pump with flange-mounted calibration module on base plate for calibration at BestSens
How to determine the axial thrust of your machine in 3 steps
All you need for axial thrust measurement
Step 1: Tell us the parameters of your application
and plan how to mount the BeMoS L8 sensors in your storage rack.
Step 2: Construct an adapter for the calibration module
and send us the setup with motor on a base plate. We can provide the CAD data of the calibration module. Just send us a mail with your request.
Step 3: We calibrate the bearing bracket for you,
play the calibration curves into the BeMoS one controller and send you back the calibrated bearing yield with measuring system. Start with your measurement.
With the demonstrator, the sensors and measuring systems for condition monitoring of pumps can be demonstrated live.
For this purpose, the typical drive train of a pump was set up on a small scale as a demonstrator in cooperation with METAX Kupplungs- und Dichtungstechnik GmbH. The demonstration gate consists of a drive that can accelerate the drive shaft to up to 2,300 rpm via a belt. A deep groove ball bearing as a fixed bearing and a cylindrical roller bearing as a floating bearing hold the shaft in position. The smart mechanical seal, as well as rolling bearing monitoring and axial thrust measurement can be demonstrated live.
Rolling bearing monitoring and axial thrust measurement
Behind the fixed bearing, a force can be applied axially to the shaft by hand via an adjusting screw and a disc spring assembly. The force can be increased from 0 Newton to approx. 300 Newton. The fixed bearing is equipped with BeMoS L8 sensors and the BeMoS one controller has been calibrated for axial thrust measurement. It can be shown that with BeMoS, on the one hand, it can be detected whether the bearing is operated in underload and the rolling elements slip (this is the case up to approx. 100 Newton minimum load). On the other hand, the axial force is determined and output as soon as a slip-free state is reached.
Axial thrust: adjustment and measurement
AXIAL THRUST MEASUREMENT