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Shaft Failures

Vane and Piston Pump Shafts

Pump shaft failures are generally caused by repeated stress. The two types of metal fatigue responsible for pump shaft failure are:

	Rotational Bending Fatigue
	Torsional Fatigue

We stock 100's of shafts including specials, Caterpillar, splines, keyes, tapers and more!

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Rotational Bending Fatigue:

This shaft broke clean at a 90° angle to its axis of rotation. The likely cause is a misalignment between the shaft and its power source that makes the shaft flex slightly with each revolution.

Fractures like this occur in areas of concentrated stress that is at least perpendicular to the shaft axis.

The marks shown on this shaft indicate that it was unevenly loaded or unbalanced. The smoother area near the edge is were the fracture started. The curved ripples get gradually courser, with a rough, shell-like spot where the shaft finally ruptured.

Torsional Fatigue:

This fatigue is caused by forces generated during normal operation. These forces, when repeated thousands or millions of times, with varying stress levels and load cycles, eventually wear the shaft out.

The fracture can take a variety of shapes, depending on the shaft geometry and loading direction. Torsion that is always in the same direction usually causes on long spiral fracture at a 45° angle to the shaft axis (as shown).

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