What Causes a Dump Truck to Miss and Slam?

Standard Operation for a Telescopic Cylinder

To explain what causes miss and slam during telescopic cylinder function, let’s first review the standard operation for a telescopic cylinder:

  • To extend the cylinder, the largest sleeve or tube moves first, then the next largest, down to the smallest sleeve or plunger.
  • When retracting the cylinder, the smallest sleeve or plunger closes or collapses first, then the next largest sleeve, up to the largest sleeve.

Incorrect Sequence Causes Mis-Staging

Mis-Staging occurs when the cylinder does not extend or retract in the correct sequences as described above.

As an example, a 3 stage cylinder may experience the following miss/slam: the largest sleeve extends properly and then the plunger starts extending before the middle (or next larger) sleeve starts to extend.  The middle sleeve finally breaks loose and shoots out, causing it and the plunger to collapse or drop back into the cylinder creating a loud banging or slamming noise.

Reasons for Missed Stages

There are several reasons the cylinder may be missing stages of the extension or retraction operation:

  1. The Pack/Seal or a Bearing on the sleeve that is not moving may be too tight, which prohibits the sleeve from extending or retracting in the proper sequence.
  2. The Cylinder that the body or unit is mounted in may have a worn or damaged part. This causes the cylinder to sideload; not allowing the sleeve to extend or retract in the correct order.
  3. A bent, egg-shaped, or bulging sleeve can cause tightness, resulting in the sleeve being unable to extend or retract appropriately.

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