Thrust balance

In this automatic thrust balancing system, the pressure behind the compressor wheel is controlled to a value between the compressor suction pressure and the wheel peripheral pressure. As the expander inlet pressure increases above the compressor suction pressure level, the resulting thrust force pushes the compressor wheel, and hence the rotor system, towards the compressor suction. In the reverse situation, when the pressure behind the compressor wheel is reduced below the wheel peripheral pressure level, the rotor system moves toward the expander. 

When the pressure behind the compressor wheel is adjusted in accordance with the magnitude of the axial force, automatic thrust balancing is achieved. The signal corresponding to the magnitude of... 

The arrangement in Figure 5-14, generally called back to back," is normally considered useful in solving difficult thrust balance problems where the conventional thrust bearing and balance drum size are inade... 

Absorb thrust loads during upset conditions and provide back-up to hydraulic thrust balancing. 

This arrangement internally utilizes back-to-back impeller arrangements providing for thrust balance without the use of a balance piston. This type of configuration has added advantages in high pressure, high case lift (pressure rise across the case) applications. 

Bearings (journal, precision faced thrust) Thrust balancing disc... 

Interstage bushings and thrust-balancing devices on multistage pumps may have the manufacturer s standard clearances, provided these clearances are stated as exceptions to this standard (see 2.6.4.2) in the proposal and are approved by the purchaser. When the manufacturer s standard clearances are based on material combinations exhibiting superior wear characteristics, supporting data shall be included in the proposal. 

Kale.R.D. et al - Analysis of failure of Axial Thrust Balancing and Thrust bearing of a small capacity boiler feed pump for a nuclear power plant, IV Asian International Conference on Fluid Machinery, Oct 1993, China. 

Back-to-back impellers allow for a balanced rotor thrust and minimize overloading the thrust bearings. 

Balance piston with no external leakage will greatly reduce wear on the thrust bearings. 

Thrust-bearing-load meters for protection against excessive loading are available on thrust bearings, and automatic thrust control, which functions by controlling the pressure behind a balancing drum, also is available. 

Rotor Seals To balance the thrust on the rotor, usually there are one or two labyrinth-type seals on the rotor. These seals often are damaged if there is dust in the incoming fluid or gas, and wear on the backside seal causes serious upsets in thrust-bearing loads. Provisions are available for coUecting and disposing of the dust which tends to accumulate in the seal so as to protect the seal from serious erosion. 

It is desirable to have additional axial-load control on the multistage compressor. A balance piston, also refeired to as the balance drum, can be located at the discharge end (see Figure 5-46). The balance piston consists of a rotating element that has a specified diameter and an extended rim for sealing. The area adjacent to the balance piston (opposite the last stage location) is vented, normally to suction pressure. The differential pressure across the balance piston acts on the balance piston area to develop a thrust force opposite that generated by the impellers. The pressure on the... 

The propulsor, in a steady situation, has to provide the thrust equivalent to the resistance of the ship. The prediction of this balance between ship resistance and propeller thrust is a complex process because the water flow in the stern region of the ship interacts with the flow through the propeller. The ship resistance may be modified by the action of the propeller, while the propeller efficiency usually is influenced by the disturbed flow regime near the stern of the ship. 

Enclosed Type Impeller Hydraulically Balanced for Reduced Thrust Load... 

Elimination of potential thrust bearing failure due to failure of the large diameter balance piston labyrinth. 

Wheels are statically balanced individually then the total assembly of wheels on the shaft is also statically and dynamically balanced. An internal balancing drum (see Figure 12-40E) is usually placed on the discharge end of the shaft to balance thrust loads. 

Figure 4-206. Hydraulic thrust and indicated weight balance for positive displacement motor. (Courtesy Smith International, Inc.)...

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