Incorrect installation dimension

Seal faces loaded with over-compressed spring tension, can generate too much heat. This will damage the o-ring and even fracture the seal laces from thermal expansion (Figure 14-13). If the spring tension is inadequate, the laces can leak after a short while as the softer face wears against the harder face, and the spring tension relaxes completely. The installation dimension is critical to long seal life.

Most seal companies provide a set of instructions and engineering schematic with each mechanical seal to help the mechanic determine the correct installation dimension. These instructions assume:

SHAFT FRETTING

Figure 14-13 ______

■ That the mechanic has the drawings available at the moment of installation. Often times, the engineer stores the drawings in a file so they won't get lost or dirty. For innumerable reasons, the mechanic rarely has a set of drawings available at the installation.

■ That the mechanic knows how to interpret engineering schematics.

■ That the instructions and schematic are printed in the mechanic's native language.

Also the shaft or sleeve should measure the correct dimension within tolerance, and have the correct surface finish:

■ The correct dimension tolerance =: +0.000:-0.002 inch. For example, a 2 inch diameter shaft can measure no greater than 2.000, and not less than 1.998 inches.

■ The surface finish = 32rms, also known by machinists as AAA

0 0

Post a comment