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Centrifugal Pumps Design and Application 2nd ed - Val S. Lobanoff, Robert R. Ross (Butterworth-Heinemann, 1992)

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380 <strong>Centrifugal</strong> <strong>Pumps</strong>: <strong>Design</strong> <strong>and</strong> <strong>Application</strong><br />

liquid. Then only the seal faces (primary <strong>and</strong> mating rings) <strong>and</strong> secondary<br />

seal come in contact with the pumpage <strong>and</strong> can be made of corrosion<br />

resistant materials such as Teflon, ceramic, <strong>and</strong> carbon. Some of the<br />

more common seal materials are shown in Table 17-3.<br />

Temperature is another consideration in seal material selection. Both<br />

secondary <strong>and</strong> static seals must remain flexible throughout the entire life<br />

of the seal. If seal flexibility is lost by hardening of the elastomer from<br />

high temperature, the seal will lose the degree of fre<strong>ed</strong>om necessary to<br />

follow the mating ring. The temperature limits for common secondary<br />

<strong>and</strong> static seal materials is given in Table 17-4. Temperature is not an<br />

issue for a metal bellows seal. This type of secondary seal is specifically<br />

design<strong>ed</strong> for high temperature <strong>and</strong> cryogenic applications beyond the<br />

limits of common elastomeric materials. However, this type of seal is<br />

limit<strong>ed</strong> in terms of corrosion resistance <strong>and</strong> most high pressure applications<br />

due to the thin construction of the bellows.<br />

Table 17-3<br />

Most Common Materials of Construction<br />

for Mechanical Seals<br />

COMPONENT<br />

SECONDARY SEALS<br />

0-RING<br />

BELLOWS<br />

WEDGE<br />

METAL BELLOWS<br />

PRIMARY RING<br />

HARDWARE<br />

(RETAINER. DISC.<br />

SNAP RING, SET<br />

SCREWS. SPRINGS)<br />

MATING RING<br />

MATERIALS OF CONSTRUCTION<br />

NITRILE, ETHYLENE PROPYLENE .<br />

PLUOROELASTOMER , PERFLUOROELASTOMER .<br />

CHLOROPRENE<br />

NITRILE. ETHYLENE PROPYLENE,<br />

FLUOROELASTQMER, CHLOROPRENE<br />

FLUOROCARBON RESIN, GRAPHITE FOIL<br />

STAINLESS STEEL, NICKEL BASE ALLOY<br />

CARBON. METAL FILLED CARSON,<br />

TUNGSTEN CARBIDE. SILICON CARBIDE,<br />

SILICQNIZED CARBON<br />

I8-8 STAINLESS STEEL,<br />

3!6 STAINLESS STEEL,<br />

NICKEL BASE ALLOYS, TITANIUM<br />

CERAMIC. CAST IRON, TUNGSTEN CARBIDE,<br />

SILICON CARBIDE

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