Thrust-bearings systems

Wang, Y., Wang, Q. and Chih, L 2001, Mixed Lubrication of Coupled Journal-thrust Bearing Systems, Submitted to Tribology International. 

Thrust-Bearing Power Loss The power consumed by various thrust bearing types is an important consideration in any system. Power losses must be accurately predicted so that turbine efficiency can be computed and the oil supply system properly designed. 

The Automatie Thrust Balanee System is a dynamie adjusting system. Hydrodynamie pressure at the thrust bearing faee, an indieation of thrust loads, is eontinuously monitored and fed to either side of a piston, whieh, in turn, adjusts the pressure aeting behind the eompres-sor wheel. 

Steam turbine considerations. The speed at whieh the turbine must operate and the steam eonditions available influenee the operating effieieney of the unit. Double-ended steam turbines require speeial eonsideration of thrust bearing sizing, overspeed proteetion, and governing systems. 

Figures 6-17 through 6-21 show simplified diagrams of AMB systems. Figure 6-18 depiets two pairs of eoils suspending the rotor about its inertial axis—as opposed to its geometrieal axis as with eonventional oil bearing systems. Thus, the rotor is self-balaneing and vibration eannot oeeur. A third pair of eoils is used for thrust eompen-sation and to determine the preeise shaft position.

When designing a system for thrust bearing proteetion, it is neeessary to monitor small ehanges in rotor axial movement equal to oil film thiekness. Probe system aeeuraey and probe mounting must be earefully analyzed to minimize temperature drift. Drift from temperature ehanges ean be unae-eeptably high. 

Journal bearing eccentricity Bearing damage Rotor-bearing system critical Coupling critical Structural resonances Thrust bearing damage... 

Failure protection. Fortunately, aeeurate and reliable instrumentation is now available to monitor thrust bearings well enough to assure safe eontinuous operation and to prevent eatastrophie failure in the event of an upset to the system. 

A critical installation should have the metal temperature sensors in the thrust pad. Axial proximity probes may be used as a backup system. If metal temperatures are high and the rate of change of those temperatures begins to alter rapidly, thrust-bearing failure should be anticipated. 

If casing limitations are fixed by user-supplied relief valves, this information should be conveyed to keep the vendor from rating the compressors on other data. Evaluations can be more of a problem if the same design basis isn t universal with all vendors. Startup and shutdown consideration influence various components, shaft end seals, seal system pressures, and even thrust bearings in some instances. The use of an alternate startup gas, or the desire to operate a gas compressor on air to aid in plant piping dryout should be covered. 

Figure 12-50B. A forced-feed lube system ensures that journal and thrust bearings are properly lubricated. The system is basicaiiy designed in accordance with APi 614 and is suitabie for continuous compressor operation. (Used by permission Bui. PROM 526/i-5/95-ii. Nuovo Pignone, S.p.A., Fiorence, itaiy New York Los Angeies and Houston, Texas. Aii rights reserved.)...

The drive system consists of a motor, a speed reducer, and thrust bearing (Figure 14-5). Obviously, the motor turns the screw and is often fairly large, as it takes a lot of power to push high viscosity molten poly-... 

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