Overhung

Whenever a hot-gas expander is employed, the thrust bearing of the compressor train is located in the expander. This coupling arrangement minimizes the coupling overhung mass, thus reducing the risk of undue... 

The design of shaft seals must strive to reduee wear of these eritieal eomponents. An overhung turbine design should use a stiff shaft that operates below its first shaft eritieal speed. This will greatly limit the extent of damage in the event of aeeidental or... 

Figure 5-13. The Elliott TH expander is a single-stage hot gas expander with an axial inlet and vertical exhaust. The TH-line expanders range in horsepower from 4,000 to 50,000 and are of overhung rotor construction. The expander consists of four major components the inlet casing and its supports, the exhaust casing, the bearing housing and support system, and the rotor.

The expander design will be of axial entry (Figure 5-14), overhung rotor, stiff shaft construction with one or two rows of blading designed and constructed for 100,000 hrs of life and at least 3 yrs of uninterrupted continuous service. It is recognized that uninterrupted operation for this period of time involves factors beyond the Seller s control. 

The maximum permissible vibration, in mils (0.001 in.), during shop test at rated speed shall be equal to the square root of 20,000 divided by the sum of rated speed plus meeh-anieal and eleetrieal runout for the overhung rotor design. Only the aetual total measured runout may be subtraeted from the unfiltered peak-to-peak amplitude measured during testing to attain the shaft vibration. The meehanieal-plus-eleetrieal runout subtraeted from the unfiltered peak-to-peak amplitude shall not exeeed 0.5 mils regardless of total runout. 

Figure 5-17. The rotor is an overhung design with the disk mounted to the inboard end of the shaft, positioned in the axiai gas fiow. Disk and biades are of Waspaioy materiai.

Clair, M., Application of Magnetic Bearings and Dry Gas Seals to an Overhung Compressor, Revolve Proceedings, April 1992. 

Single stage (single-suetion) Overhung Pipeline Multistage... 

Overhung rotors present an easier alignment problem beeause shaft-end alignment is neeessary only at the eoupling between the eompressor and driver. 

High-speed eouplings must be balaneed very earefully and, with a low overhung moment, the effeet of eoupling overhung moment is felt not only in maehine bearing load but in shaft vibration. 

Another common type of compressor is manufactured in an integrally geared configuration. It is basically an overhung style machine mounted on a gear box and uses the gear pinion shaft extension to mount an... 

Figure 5 1. Single-s, verttcally split, overhung style centrifugal compressor. Courtesy of Elliott Companyi...

Figure 5-3. Overhung, gearbox mounted centrifugal compressor. Courtesy of Atlas Copco Comptec fnc.)...

Figure 5-4. Diagram of a single-stage overhung type centrifugal compressor.

Vibration and failure are particularly liable to occur when a small-diameter pipe carries a heavy overhung weight. Within 30 minutes of the start of a new compressor, a pressure gauge fell off for this reason [24]. 

Figure 3-48. Upper limits of specific speeds for single suction overhung impeller pumps handling dear water at 85°F at sea level. (By permission, Hydraulic Institute Standards for Centrifugal, Rotary, and Reciprocating Pumps, Hydrauiic Institute, 13th ed., 1975.)...

ARR. 2 SWSI For belt drive or direct connection. Impeller overhung. Bearings in bracket supported by fan housing. 

ARR. 4 SWSI For direct drive Impeller overhung on prime mover shaft. No bearings on fan Prime mover base mounted or integrally directly connected. 

ARR. 9 SWSI For bell drive Impeller overhung, two bearings, with prime mover outside base... 

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