Bearing Clearance Measurement in Tilting Pad Journal Bearings

Measuring the bearing clearance in tilting pad journal bearings during assembly or before commissioning is a common procedure for checking the actual condition. The measurement ensures that the bearing clearance is sufficient and corresponds to the specified values.

An insufficient bearing clearance can lead to damage of the bearing shell or the shaft. The validation of the correct bearing clearance is also important because it has a significant influence on the rotordynamic behavior of the machine.

There are different options for measuring the clearance in tilting pad journal bearings. One of the most popular options for measuring the clearance is the use of lead inserts. In this case, lead inserts are placed between the shaft and the bearing pads during assembly of the journal bearing. After disassembly of the bearing body, the bearing clearance can be determined by measuring the lead inserts. Another method of measuring the bearing clearance is to lift the rotor after assembly of the journal bearings. Here it is essential to know how the journal pads are located in the bearing body and in which direction the load vector is oriented.

In the following, we would like to explain the rotor lifting method for bearing clearance measurement in more detail.

Measurement of the bearing clearance by lifting the shaft in tilting pad journal bearings

If the center of the shaft and the center of the bearing bore are identical, the radial bearing clearance can be determined as the gap “C/2” between the shaft and the bearing shell above each pad support point.

The displacement of the shaft from this position to the pad surface corresponds exactly to “C/2”. This is different if the shaft is moved from this position into a gap between two pads. The displacement of the shaft in the direction of a gap between two pads is greater than the radial bearing clearance. The additional drop value “u” must therefore be taken into account when calculating the real bearing clearance.

The total lift value of the shaft in journal bearings depends on the number of pads and the load direction. For the load direction “load between pads”, the following drop values and total lift values must be taken into account:

For the load direction “load on pad”, the following drop values and total lift values have to be considered:

If you are interested in more detailed information about the different options for measuring the clearance in tilting pad journal bearings, please do not hesitate to contact us.??

Kindly we want to remind you that Miba's recommendations for the use of its products are based on experience and technical standards, and do not represent any assurance of characteristics or warranty commitments. Any warranty or guarantee of merchantability or fitness for a particular purpose is excluded. Thank you for your well-understanding.