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6
Effective Weight
Effective weight is an important factor in selecting shock
absorbers . A shock absorber “sees” the impact of an
object in terms of weight and velocity only; it does not
”see” any propelling force . The effective weight can
be thought of as the weight that the shock absorber
“sees” on impact . Effective weight includes the effect
of the propelling force on the performance of the shock
absorber .
Failing to consider the effective weight may result in
improper selection and poor performance of the shock
absorber . Under extreme conditions, an effective weight
that is too low may result in high forces at the start of
stroke (high on-set force) . However, an effective weight
that is too high for the shock absorber may cause high
forces at the end of stroke (high set-down force) .
Consider the following examples:
1 .) A 5 lb (2 .27 kg) weight travelling at 25 ft/sec (7 .62
m/s) has 625 lbs (71 Nm) of kinetic energy (figure A) .
On this basis alone, a MA 3325 would be selected .
However, because there is no propelling force, the
calculated effective weight is five pounds – which is
below the effective weight range of the standard MA
3325 . This is a high on-set force at the start of the
stroke (Figure B) . The solution is to use a speciallyorificed
shock absorber to handle the load .
2 .) A weight of 50 lbs (22 .68 kg) has an impact velocity
of 0 .5 ft/sec (0 .15 m/s) with a propelling force of
800 lbs (111N) (Figure C) . The total impact energy
is 802 .5 inch-pounds . Again, a MA 3325 would be
selected based just on the energy . The effective
weight is calculated to be 16,050 pounds (7,280
kg) . This is well above the range of the standard MA
3325 . If this shock absorber is used, high-set-down
forces will result (Figure D) . In this case, the solution
is to use a ML 3325, which is designed to work in
low-velocity, high-effective weight applications .
Computer-Aided Simulation
By combining application data with a shock absorbers
design parameters, ACE engineers can create a picture
of how the shock will perform when impacted by the
application load . Peak reaction force, peak deceleration
(G’s), time through stroke, and velocity decay are
identified with extreme accuracy . The user benefits by
having the guesswork taken out of sizing decisions and
by knowing before installation how his shock problem
will be solved .
Simulation is also used to maximize the performance
of ACE adjustable models by predicting the ideal
adjustment setting for a particular group of conditions .
By using simulation software during product
development stages, ACE has maximized the
performance of its entire line of deceleration devices for
over two decades .
Figure A
Figure B
ACE Controls Inc. · 800-521-3320 · (248) 476-0213 · Fax (248) 476-2470 · www.acecontrols.com · email: shocks@acecontrols.com
Force
Figure C
800 lbs
(111 N)
Figure D
Force
Low Effective Weight
25 ft/sec (7.62 m/s)
5 lbs
(2. 27 kg)
Low Effective Weight
Stroke
High Effective Weight
Example 2: Orifice Area Is
Too Large (High Set-Down)
Linear
Deceleration
Example 1: Orifice Area Is
Too Small (High On-Set)
High Effective Weight
0.5 f/s (0.15 m/s)
50 lbs
(22.68 kg)
Air-Oil Systems, Inc. www.airoil.com
Stroke
Linear
Deceleration