What does running clearance refer to?

Running clearance is the specific gap between the moving parts of a machine, particularly in bearings, when the machinery is at its operational temperature. As machines operate, they experience thermal expansion, which can alter the dimensions of the components due to the heat generated from friction and other factors. This phenomenon makes determining the clearance at this temperature critical for ensuring proper function and longevity of the machinery.

When the machine heats up, the materials expand, which in turn affects the tolerances. Running clearance must be carefully managed; too little clearance can lead to seizures or excessive wear, while too much clearance can result in loss of efficiency and increased vibration. Therefore, understanding running clearance is essential for anyone working with rotating machinery, as it directly impacts performance, reliability, and maintenance needs.

In contrast, the other options refer to different phases or measurements that do not capture the dynamic aspect of the machine in operation. Initial assembly clearance pertains to the spacing established before the machine begins operating, while maximum clearance achievable is a theoretical measure under ideal conditions, not representative of actual operating conditions. The measurement before lubrication does not account for the changes in clearance during normal running, which is critical for analyzing performance under real conditions.