Centrifugal Pumps Design and Application 2nd ed - Val S. Lobanoff, Robert R. Ross (Butterworth-Heinemann, 1992)
Mechanical Seats 385 steam, is to prevent the buildup of any carbonized or crystallized material along the shaft. When properly applied, a seal quench can increase the life of a seal installation by eliminating the loss of seal flexibility due to hangup. A flush, vent and drain gland plate is used where seal leakage needs to be controlled. Flammable vapor from a seal can be vented to a flair and burned off, while non-flammable liquid leakage can be directed to a sump. Figure 17-22 illustrates some common restrictive devices used in the gland when quench or vent and drain connections are used. These bushings may be pressed in place, as shown in Figure 17-22A, or allowed to float, as in figures 17-22B, C and D. Floating bushings allow for closer running fits with the shaft because such bushings are not restricted at their outside diameter. Floating bushings in Figures 17-22C and D, are Figure 17-22. Common restrictive devices used with quench or vent-and-drain gland plate.
386 Centrifugal Pumps: Design and Application Flgyre 17-23. Seal face design for upstream pumping (courtesy of John Crane), also sized to fit the diameter of the shaft. Small packing rings may also be used for a seal quench as shown in Figure 17-22E. Shaft sleeves should be used on all applications where the shaft must be protected from the environment of the pumpage. Sleeves should be made of corrosion and wear resistant materials. Sleeves must be positively secured to the shaft and seal at one end. The sleeve should extend through the gland plate. Upstream Pumping The concept of upstream pumping is new to the sealing industry and is a further refinement of spiral groove technology developed for dry running gas compressor seals. Upstream pumping is defined as moving a small quantity of liquid from the low pressure side of a seal to the high pressure side. This is accomplished by a change in seal face geometry and by incorporating spiral grooves, Figure 17-23. A conventional flat seal design is only capable of preventing leakage from a higher pressure stuffing box to atmosphere. A seal designed with the upstream pumping feature can seal high pressure and move clean liquid across the seal faces to a high pressure stuffing box. This type of design creates a full liquid film at the faces and reduces horsepower loss. This is also a new way to flush a seal face with just a few cc/minute
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386 <strong>Centrifugal</strong> <strong>Pumps</strong>: <strong>Design</strong> <strong>and</strong> <strong>Application</strong><br />
Flgyre 17-23. Seal face design for upstream pumping (courtesy of John Crane),<br />
also siz<strong>ed</strong> to fit the diameter of the shaft. Small packing rings may also be<br />
us<strong>ed</strong> for a seal quench as shown in Figure 17-22E.<br />
Shaft sleeves should be us<strong>ed</strong> on all applications where the shaft must be<br />
protect<strong>ed</strong> from the environment of the pumpage. Sleeves should be made<br />
of corrosion <strong>and</strong> wear resistant materials. Sleeves must be positively secur<strong>ed</strong><br />
to the shaft <strong>and</strong> seal at one end. The sleeve should extend through<br />
the gl<strong>and</strong> plate.<br />
Upstream Pumping<br />
The concept of upstream pumping is new to the sealing industry <strong>and</strong> is<br />
a further refinement of spiral groove technology develop<strong>ed</strong> for dry running<br />
gas compressor seals. Upstream pumping is defin<strong>ed</strong> as moving a<br />
small quantity of liquid from the low pressure side of a seal to the high<br />
pressure side. This is accomplish<strong>ed</strong> by a change in seal face geometry<br />
<strong>and</strong> by incorporating spiral grooves, Figure 17-23.<br />
A conventional flat seal design is only capable of preventing leakage<br />
from a higher pressure stuffing box to atmosphere. A seal design<strong>ed</strong> with<br />
the upstream pumping feature can seal high pressure <strong>and</strong> move clean liquid<br />
across the seal faces to a high pressure stuffing box. This type of<br />
design creates a full liquid film at the faces <strong>and</strong> r<strong>ed</strong>uces horsepower loss.<br />
This is also a new way to flush a seal face with just a few cc/minute
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