Sealing design

A. J. Baumgartner, ia R. A. Burton, ed.. Bearing and Seal Design in Nuclear Power Machiney, American Society of Mechanical Engineers, New York, 1967. 

Pre.s.sure. Pressure affects the choice of material and whether balanced or unbalanced seal design can be used. Most unbalanced seals are good up to 100 psig stuffing box pressure. Over 100 psig, balanced seals should be used. 

Lubricity. In any mechanical seal design, there is rubbing motion between the dynamic seal faces. This rubbing motion is often lubricated by the fluid being pumped. Most seal mauufac turers hmit the speed of their seals to 90 ft/sec (30 m/sec). This is primarily due to centrifugal forces acting on the seal, which tends to restrict the seal s axial flexibihty. 

Double seals are standard with toxic and lethal products, but maintenance problems and seal design contribute to poor reliabihty. The double face-to-face seal may be a better solution. 

Controlled Lrrading - The grip onto the shaft is determined by the seal design and the machined groove, and not the mechanic s ability to install the seal at the proper dimension and spring loading. 

Cartridge Seal designs comply with most pump standards like ... 

Although the balance feature, o-rings, and the cartridge concept were discussed in detail in the previous chapter, here is a brief review why this seal design will give your pumps their best chance for extended leak-free service with reduced maintenance costs. 

Turboexpander manufacturers and dry gas seal vendors recognizing the above limitation, worked together to develop a dry gas seal design that is an excellent compromise given the space limitation and customer requirement. Figure 6-16 shows a cross-section of the dry gas seal developed for turboexpanders. 

The physieal and ehemieal properties of the liquid being sealed will plaee eonstraints upon the type of seal arrangement, the materials of eonstruetion, and the seal design that ean be used. 

Pressure. The relative pressures of the material to be sealed affeet the deeision of whether to use a balaneed or unbalaneed seal design. Pressure also affeets the ehoiee of faee material beeause of the seal-faee loading. 

If the serviee happens to be below atmospherie pressure, then speeial eonsiderations are required to seal the material effeetively. Most unbalaneed seal designs are applieable up to 100 psig (7 Bar) stuffing-box pressure. At more than 100 psig (7 Bar), balaneed seals should be used. 

Common seal designs may handle fluid temperatures in the 0°F to +200 °F (—17°C—93°C) range. When temperatures are above the +200 °F... 

Immediately after the running test, any compressor intended for toxic, hazardous, flammable, or hydrogen-rich service should be gas tested with an inert gas to the maximum seal design pressure. The test is held at least 30 minutes and the casing and its joints checked for leaks, using a soap bubble method or other suitable means for leak detection. When no leaks are detected, the compressor will be considered acceptable. 

All flares must be provided with flashback protection to prevent a flame front from travelling back to the upstream piping and equipment. A number of different flashback seal designs are available, of which the seal drum is used in nearly all applications. Key design details are summarized below ... 

The mode of operation, whieh ean be bateh, fed-bateh, or eon-tinuous, should be eonsidered during the preliminary stages of large-seale design. Bateh operation often involves simplieity in maintenanee of aseptie eonditions and minimizes operating losses due to eontami-nation or equipment failure. 

Figure 3-22 is an outside balanced seal designed for vacuum to 150 psig and -40°F to -l-400°F. (See Table 3-4) The process fluid must be free of solids (as for practically... 

Metal can cover many requirements in seal design it may be used for faces and other parts such as rings and bellows. The specification of the metal depends on the degree of corrosion resistance necessary, the thermal expansion and the material of the mating face. 

Mechanical seal designs are referred to as friction drives, or single-coil spring seals, and positive drives. 

Nevertheless, the simple and reliable coil spring seal has proven itself in the pumping industry and is often selected for use despite its drawbacks. In regulated industries, this type of seal design far exceeds the capabilities of a compressed packing ring seal. 

The work shows that compaction and swelling effects should be included in assessments when sealing high-pressure oil-field fluids. Housing and/or seal design should be such that these effects are minimized. 

A great variety of mechanical seal designs are available, and seals can be found to suit virtually all applications. Only the basic mechanical seal is described below. Full details, and specifications, of the range of seals available and their applications can be obtained from manufacturers catalogues. 

Velocity seals are more recent developments in air seal design. They use conical baffles to redirect and focus the purge gas flow field just below the flare tip to sweep air from the flare stack. Some velocity seal designs can reduce the purge gas flow rate requirement to about 1/10 of the rate needed without the seal. Also, some velocity seal designs reportedly require only about 25 to 33 percent of the purge gas used in diffusion seals (AICliE-CCPS, 1998). More details about air (purge reduction) seals may be found in API RP 521 (2007). 

Nevertheless, Ni(-Fe)-Cr base alloys may find application as interconnect materials through the use of innovative SOFC stack and seal designs and novel interconnect structures. For example, a cladding approach has been applied to fabricate a stable composite interconnect structure consisting of FCC Ni-Cr base alloy claddings on a BCC FSS substrate [134,135], The clad structure appeared to be stable over 1000 hours at 800°C in air and exhibited a linear CTE close to that of the FSS, but needs further long-term stability evaluation before its commercial use. 

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