Gaskets are materials used to seal one compartment of a device ...
Gaskets are materials used to seal one compartment of a device ...
Gaskets are materials used to seal one compartment of a device ...
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Fibrous glass packings <strong>are</strong> usually divided in<strong>to</strong> two groups, “E” glass<br />
packings, and “S” glass packings, depending upon the type <strong>of</strong> glass fiber <strong>used</strong><br />
in the formulation. “E” glass is <strong>one</strong> <strong>of</strong> the more common glass fibers, and is<br />
<strong>of</strong>ten manufactured in<strong>to</strong> a packing which is <strong>used</strong> as a jacket around a plastic<br />
core <strong>of</strong> carbon or aramid fibers, and other <strong>materials</strong> (OGJ 1986).<br />
“E” glass packings <strong>are</strong> suitable for applications where the operating<br />
temperature is below 1000°F. Above this temperature, the packing loses 50<br />
percent <strong>of</strong> its tensile strength. Also, the material can be <strong>used</strong> with most<br />
fluids except strong caustics.<br />
The second type <strong>of</strong> fiber, ~ glass, was developed by NASA and is<br />
recognized as the superior glass fiber in use <strong>to</strong>day (OGJ 1986). This material<br />
is generally <strong>used</strong> as a jacket around a core <strong>of</strong> graphite and other fibers. The<br />
packing is caustic resistant and can be <strong>used</strong> in applications with operating<br />
temperatures <strong>of</strong> 1500°F(OGJ 1986).<br />
One disadvantage <strong>of</strong> glass packings is the abrasive nature <strong>of</strong> the material.<br />
In high shaft-speed applications, the abrasiveness <strong>of</strong> glass wears down the<br />
shaft stem requiring frequent replacement <strong>of</strong> the stem.<br />
Glass packings will<br />
capture 30 percent <strong>of</strong> the <strong>to</strong>tal asbes<strong>to</strong>s packing market and will cost twice as<br />
much as the asbes<strong>to</strong>s material. Thus, the price will be $60.40 per pound<br />
(Palmet<strong>to</strong> Packing,<br />
ICF 1986a).<br />
John Crane-Houdaille, previously <strong>one</strong> <strong>of</strong> the major producers <strong>of</strong> asbes<strong>to</strong>s<br />
packings, <strong>of</strong>fers an “S”-glass yarn packing replacement that it claims is<br />
better than the asbes<strong>to</strong>s packings it replaces. It has a higher temperature<br />
limit, good service life in caustics, steam, oil, liquid petroleum, and<br />
chemicals, a high pressure limit <strong>of</strong> 7700 psi and will not score valve stems or<br />
other pieces <strong>of</strong> equipment in which it is <strong>used</strong> (John-Crane 1987).<br />
3. PBI Mixtures<br />
PBI (polybenzimidazole) is produced by Celanese Engineering. It has a<br />
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