|
The
use of Micro-cellular foam inserts has produced a
new breed of shocks, which are more resistant to
fade. After heavy work, all shock absorbers,
whether they are hydraulic, gas or foam cell
shocks, show signs of fade or lack of damping
force. However, Foam Cell shock absorbers are far
more resistant to fade than other types of shocks.
Tests have shown that foam cell shocks
maintain almost optimum efficiency in conditions
that can cause gas and especially hydraulic shocks
to lose much of their dampening force.
To understand how foam cell shock absorbers could
produce such superior performance, we will look at
the common causes of fade and how foam cell
inserts affect shock absorber operation.
AERATION is the mixing of the oil with gas or air
in the oil reservoir, i.e. the outside cylinder of
the shock. This causes the oil to
"FROTH", reducing its viscosity so that
it passes more freely through the valving. This
causes the shock to lose some of its damping force and the air
bubbles passing through the valving causes the
shock to operate unevenly and noisily.
Also, when aerated, the oil is compressible. Instead
of the oil being forced through the valving and
into the outer cylinder, the action of the shock
absorber compresses the oil within the pressure
cylinder. When extremely aerated, a shock provides
a cushioning effect rather than a controlled
resistance to movement. This is loosely called
"FADE".
CAVITATION occurs when the oil inside the pressure
chamber starts to boil. This is due more to LOW
pressure than to high temperature, although both
contribute to cavitation.
The pressure drop is caused when the shock extends
Rapidly, but the flow of oil into the pressure
chamber is insufficient to fill the space left by
the retreating piston and rod. A vacuum is created
in the pressure cylinder and the oil begins to
boil. Under low pressure, a liquid can in fact boil
without heating, and this is what occurs when a
vacuum is created inside a shock absorber-
instantaneous boiling due to a sudden drop in
pressure. The boiling of the oil produces air
bubbles within the shock, which produces the same
effects as aeration of the oil.
Gas pressurization of shock absorbers can
significantly improve their performance, however
gas shocks are also subject to aeration &
cavitation. Under unrelenting and extremely rough
conditions a gas shock provides only marginally
resistance to fade than a standard hydraulic unit.
The FOAM CELL shock absorber, on the other hand,
performs with an almost negligible reduction in
dampening force. To do this, it must virtually
eliminate aeration & cavitation. How does it
do this?. Quite simply. The foam cell insert occupies the
space in the oil reservoir which in the case of
hydraulic or gas shock absorbers would contain air
or gas. While oil can mix with air and even
pressurized nitrogen, it cannot mix with the foam.
The foam used in shocks has tiny closed cells,
which contain bubbles of gas. The oil inside the
shock cannot mix with the gas bubbles inside the
foam because they are enclosed inside the foam.
When the shock is compressed, the foam works not
like a sponge absorbing the oil, but rather like a
spring or air bag. At the end of the compression
stroke, the compressed gas bubbles inside the foam
push the oil back into the pressure cylinder.
No oil / air or oil / gas mixture has occurred, so
there is no risk of aeration. The pressure
extended by the foam pressing the oil back into
the pressure cylinder prevents cavitation
occurring. Hence, no aeration and minimal
cavitation for unrivalled resistance to fade.
Extraordinary
features :
-
 Rod
Wiper Seal
-
Multi
Lip Seal
-
Massive
18mm Rod
-
Hardened
Sintered Piston Rod
-
Double
Chrome Plated Rod
-
High
Temperature Resistant Fluid with Twin Tube
Design
-
Massive
41mm Bore
-
Custom
made for each 4WD
-
Valved
tuned to match OEM or Tough Dog Spring rate
-
OEM
or Longer Length Shocks to suite Standard or
Raised 4WD for maximum articulation, comfort,
safety & durability
-
2
year / 40,000km Warranty (Refer Important Notice &
Conditions on Warranty).
Both
the Heavy Duty Foam cell and Gas Charged shock
absorbers come with multi stages velocity
sensitive valving and large piston for better
control and damping, larger twin tube design for
more fluid retention and longer piston travel,
multi-viscosity synthetic oil for better heat
resistant and the high quality heat and wear
resistant piston and shaft wiper seals for longer
life which are all lacking in the cheap original
shock absorbers and even in some of the
aftermarket shock absorbers.
Further more, most of the Tough Dog shock
absorbers come with 2 or sometime 3 different
lengths for different raised height applications
(i.e. the original length to suit the original
springs height and the longer lengths to suit the
raised height of Tough Dog springs) because when a
vehicle is raised by higher rate springs, it would
certainly need to replace the original length
shock absorbers with a set of longer length (which
is equivalent to the amount of height
raised) shock absorbers as otherwise, the
travel of the shock piston rod would not be
sufficient to give a good and stable ride on the
road and good wheels' articulation when off-roading.
A shock absorber cannot be too short or too long
than necessary. A too short a shock absorber would
cause the piston to hit against the top of the
shock absorber when the vehicle body is bounced up
by its springs or doing a sharp cornering or
braking. A too long a shock absorber would cause
the piston to hit against the bottom of the shock
absorber during its downward stroke or doing a
sharp cornering or braking. Too long or too short
a shock absorber would not only constitute to an
un-comfortable and un-safe ride it would also
damage the shock absorber itself in a very short
period of time. Tough Dog shock absorbers are the
only one that have come up with the different
lengths and the different type of shock absorbers
to suit the different leaf sprung and coil sprung
4wds, the different applications and the different
vehicle's raised height as Tough Dog does not
believe in giving its customers a compromised
suspension system ! Tough Dog shock absorbers
are also valve coded to match each vehicle's
weight, weight distribution and the rate of the
original springs or Tough Dog springs.
|
