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Shock Absorber Theory cont'd
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Equally as important, automotive-style shock absorbers are designed to absorb only a specific amount of input energy. This means that, for any given geometric size of automotive shock absorber, it will have a limited amount of absorption capability compared to the industrial type.
This is explained by observing the structural design of the automotive type and the lower strength of materials
commonly used. These materials can withstand the lower pressures commonly found in this type. The industrial shock absorber uses higher strength materials, enablingit to function at higher damping forces.
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Damping Force
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Adjustment Techniques
A properly adjusted shock absorber safely dissipates energy, reducing damaging shock loads and noise levels. For optimum adjustment setting see useable adjustment setting graphs. Watching and “listening” to a shock absorber as it functions aids in proper adjustment.
To correctly adjust a shock absorber, set the adjustment knob at zero (0) prior to system engagement. Cyclethe mechanism and observe deceleration of the system.
If damping appears too soft (unit strokes with no visual deceleration and bangs at end of stroke), move indicator to next largest number. Adjustments must be made in gradual increments to avoid internal damage to the unit (e.g., adjust from 0 to 1, not 0 to 4).
Increase adjustment setting until smooth deceleration orcontrol is achieved and negligible noise is heard when the system starts either to decelerate or comes to rest.
When abrupt deceleration occurs at the beginning of the stroke (banging at impact), the adjustment setting must be moved to a lower number to allow smooth deceleration.
If the shock absorber adjustment knob is set at the high end of the adjustment scale and abrupt deceleration occurs at the end of the stroke, a larger unit may be required.
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Shock Absorber Performance When Weight or Impact Velocity Vary
When conditions change from the original calculated data or actual input, a shock absorber’s performance can be greatly affected, causing failure or degradation of performance. Variations in input conditions after a shock absorber has been installed can cause internal damage, or at the very least, can result in unwanted damping performance. Variations in weight or impact velocity can be seen by
examining the following energy curves:
Varying Impact Weight: Increasing the impact weight (impact velocity remains unchanged), without reorificing or readjustment will result in increased damping force at the end of the stroke. Figure 1 depicts this undesirable bottoming peak force. This force is then transferred to the mounting structure and impacting load.
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Varying Impact Velocity: Increasing impact velocity (weight remains the same) results in a radical change
in the resultant shock force. Shock absorbers are velocity conscious products; therefore, the critical relationship to impact velocity must be carefully monitored. Figure 2 depicts the substantial change in shock force that occurs when the velocity is increased. Variations from original design data or errors in original data may cause damage to mounting structures and systems, or result in shock absorber failure
if the shock force limits are exceeded. |
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