Page 109 - GarlockFluidSealing2010

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Gasketing Terms
American Bureau of Shipping
Garlock styles on the American Bureau of Shipping
Type Approval program:
• ST-706
• BLUE-GARD® 3000, 3200
• GRAPH-LOCK® 3125SS, 3125TC
• GYLON® 3500, 3504, 3510
• IFG® 5500*
• 8459**
• 9200
• G-9900*
• 2400
Anti-Stick
While we prefer that gaskets be installed with only the
factory-applied anti-stick, experience shows that additional
anti-stick is helpful in some situations, such as areas where
fanges cannot be separated easily. Coatings should be as
light as possible. Dry powders are strongly recommended
over pastes and grease-type compounds, which can drasti-
cally reduce the crush strength and blowout resistance of
the gasket. Additionally, grease or paste type materials
may deteriorate or dissolve in service, leaving a possible
leak path across the gasket.
Aviation Gasoline
Gasoline with a high octane number is used for prop
driven airplane engines, as opposed to jet fuel for jet
engines. Aviation gasoline contains a high percentage of
aromatics. GYLON® is preferred; compressed sheet styles
with nitrile binders can be successful in some applications
(see Jet Fuel). Consult Engineering if you are unsure.
Bubble Tests
Some end users perform bubble tests of their sys-
tem to check gasket tightness. This information is helpful
before specifying a gasket. Bubble tests are an extremely
tough test for a gasketed joint, and may not be an ap-
propriate means to verify correct installation. Lightweight
fanges with low available compressive load may never
achieve "bubble tight" results.
Chlorine Service
We recommend our GYLON® styles for chlorine. The
style selection is made based on fange information. Style
3510 is listed in the Chlorine Institute’s Pamphlet 95.
Garlock Metallic Gasket Division products are also listed,
including the GRAPHONIC® gasket.
Compression
The amount of compression expected on a particular
gasket type depends on its compressibility data and the
load applied. Sealing problems are often a result of lack of
compression. Graphs of compression vs. Ioad on popular
gasketing styles are available upon request. Close toler-
ance sheet should be considered for applications requiring
tight internal clearances such as split case pumps (see
Modulus of Elasticity).
Compressive Stress
Undercompression: Underloaded gaskets will have
higher leak rates and lower blowout resistance than prop-
erly loaded gaskets. This has a profound effect on perfor-
mance and is the most frequent cause of joint problems.
Overcompression: Overcompression can lead to
crushing, which accelerates the degradation of the gasket
and can even cause immediate failure.
Uneven Compression: Gaskets resist blowout based
on the friction of the gasket against the fange. The higher
the compressive load, both initially and during service, the
higher the blowout resistance. When areas of high and
low compression exist in a fange joint, the areas of low
compression are prime candidates for blowout.
Crush Strength
Garlock recommends a maximum compressive stress
of 15,000 psi on compressed fber and GYLON ® gasket-
ing, and 10,000 psi on GRAPH-LOCK® gasketing. The
actual crush strength of these materials is typically higher
than that of homogeneous rubber.
Cryogenic Service
We recommend our GYLON® styles down to
-450°F (-268°C), and our compressed sheet gasketing is
typically recommended to -100°F (-75°C).
Dielectric Breakdown Voltage
Many applications require a gasket which is not
a good conductor of electricity. Garlock has dielectric
breakdown voltage test data available on our most popular
gasketing styles. Generally speaking,
GYLON® styles and compressed sheet that does not use
carbon or graphite fbers have high dielectric breakdown
values. Under humid or wet conditions, Styles 3504 and
3565 are particularly resistant to dielectric breakdown.
* Accepted for use where “fre safe” requirements are specifed by ABS
rules, and US Coast Guard regulations.
** Non-stocked item.