Shaft sealing arrangements

Figure 12-51 A. Multistage centrifugal compressors shaft seal arrangements. (Used by permission A C Compressor Corporation.)...

Efficiency and power cost, at normal duty and other required duties. Adequacy of shaft sealing arrangement and other rubbing seals where applicable. 

Because of the high pressure inside the steam turbine casing, a special shaft sealing arrangement must be applied between the outer casing and the turbine rotor. Typically, contactless and wear-free labyrinth seals are used, which have the... 

Because these machines require internal lubrication of the sliding-vane surface, no extreme effort is made to arrange special bearing and shaft seals, except that a gas seal of the conventional mechanical design is usually used to prevent gas from escaping to the outside or to prevent air inleakage in the case of vacuum service. For hazardous or... 

Fig. 19. Vertical cross-section of the wiper-blade reactor. A, Sealing arrangement B, gas phase C, rotor D, sealing E, bearing F, excess gas flow G, gas collected from the liquid exit H, overflow vessel I, liquid exit J, rotor blades K, gas feed L, adjustable shaft M, baffles N, reactor shell O, cooling jacket P, cooling water feed and exit Q, sampling port R, grooves S, liquid phase T, gas-liquid interface U, top and bottom plates and V, liquid feed. (After Manor and Schmitz, 1984 also from Chaudhari et al., 1986, by courtesy of Marcel Dekker, Inc.).

Butterfly valves can provide tight shut-off when soft seats are used, and their major application in chlorine service is in the larger pipe sizes. The usual design features standard adjustable packing, a wetted shaft/disc arrangement, and a one-piece soft-hp seal. Fully lined butterfly valves have lower pressure ratings and are suited only for gas applications. Fluoropolymer resin liners cover all internal surfaces. Back-up liners, not exposed to the chlorine, provide seats. Butterfly valves can provide tight shut-off with quarter-turn operation. Like the other types of valve, they should have blowout-proof stems. 

Liquid-ring pumps require shaft seals. A simple lantern-ring arrangement appears on some models and requires a flow of cooling liquid. Recycled liquid is acceptable in this duty. However, mechanical seals are preferred in most chlorine-handling applications. Double seals with separate supplies of clean fluid are the standard. 

Special shaft sealing system and pulling arrangement for the shaft seal Liners at clamps for pipe fittings and for alignment and dip pipes should be made of Teflon... 

Figure 9J5 High pressure mechanical seal (GRASSEL/BURGANN) 1, blocking circuit I 2, mechanical seals arranged back-to-back 3, blocking circuit II 4, mechanical seal 5, shaft.

The housing elements, rotor, and stator are of spheroidal graphite iron or of material that is resistant to cavitation and corrosion. The shaft is of high-quality, heat-treatable steel and the shaft extensions are normally finished to DIN standards although other arrangements are possible. Oil is used as a lubricant for the bearings and radial-lip-type shaft seals or labyrinth seals are normally fitted. Mechanical end-face seals can be provided. 

The journal bearings are of the tilting-pad type with babbitt-lined steel pads. They are made in two halves and arranged for forced-feed lubrication. Thus turbine-shaft seals are of the stepped-labyrinth type, with the labjninths flexibly moimted. 

Interna] and External Seals Mechanical seals are classified broadly as internal or external. Internal seals (Fig. 10-112) are installed with all seal components exposed to the fluid sealed. The advantages of this arrangement are (1) the ability to seal against high pressure, since the hydrostatic force is normally in the same direction as the spring force (2) protection of seal parts from external mechanical damage and (3) reduction in the shaft length required. 

Too few people eonsider the equipment with the seal seleetion. In most eases, poor equipment will give poor seal performanee, regardless of the seal or arrangement ehosen. Also, beware that different pumps with the same shaft diameter and TDH may present different sealing problems. (Note These same eonsiderations may be used for troubleshooting.)... 

It is important to seal the glands on the turbine shaft, and a typical arrangement is illustrated in Figure 14-24. Thrust bearing failures can be serious problems for steam turbines and other mechanical drives, as well as the bearings used on the driven equipment. 

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