Turbo-machine with a balance piston

Details Turbo-machine with a balance piston Turbo-machine with a balance piston

1996-09-17

1998-02-03

Kwon, John T.

Rotary kinetic fluid motors or pumps

With shaft connected fluid force subjected thrust balancing...

415107, F01D 300

Patent

active

057137200

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

During the operation of fluid-flow machines, reaction forces are transmitted onto the shaft which have, in turn, to be transmitted from the latter onto the fixed housing. Since it is undesirable to direct these forces exclusively via the shaft bearing, various compensating and balancing devices have been developed. In a known compensating device (Pfleiderer: Die Kreiselpumpen (Centrifugal Pumps), 1949, pages 366-368), the entire axial force is transmitted via a pressure plate, connected in a rotationally fixed fashion to the shaft, onto an end face of the housing which, together with the pressure plate, encloses a choke gap through which radial flow occurs. A low pressure is applied to it on its rear side, and a higher, choked-off pressure of the machine is applied to it on the choke-gap side. In operation, a choke gap is set up which depends on the difference between these pressures and permits contactless force transmission in the case of constant through flow and constant operating conditions. The shaft must be axially movable so that the choke gap can be set up in accordance with the pressure difference. For reasons of operational reliability, this is impossible in many cases in which, therefore, the application of a compensating plate is prohibited. Recourse is made in these cases to a so-called balancing piston. This is a ring which is firmly arranged on the shaft and rotates with as little play as possible in the bore of a fixed housing part and to which a higher fluid pressure is applied on one side than on the other. The force thereby resulting on the balancing piston serves to balance a bearing which determines the axial position of the shaft. With regard to operational reliability, the axial gap between the circumference of the balancing piston and the bore of the housing cannot drop below a certain minimum. The result is a high leakage which can amount to 4-6% of the flow rate and can therefore substantially impair the overall efficiency.
This high leakage can be prevented by providing the balancing piston with a ring which can rotate freely with respect to said piston and instead of the balancing piston is sealed with respect to the housing, and does not rotate with respect to the housing but can move axially together with the balancing piston (U.S. Pat. No. 2,221,225). This ring is seated in a circumferential groove of the balancing piston, its end faces enclosing two narrow gaps with the sides of the groove, which are parallel to said piston. During operation, the ring is to occupy an approximately central position between the groove sides. The leakage flow is then determined by the width of the two end-face gaps. The distance to the groove bottom has no effect, since it is very large. Contact between the ring and the balancing piston is normally not to occur during operation. This known arrangement has the disadvantage that the size of the leakage flow and the dynamic behaviour of the ring depend on the play between the end faces of the ring and the groove sides, and thus on the manufacturing tolerances and wear. It also tends to unstable behaviour.


SUMMARY OF THE INVENTION

It is therefore the object of the invention to provide a balancing arrangement of the last-mentioned type which is of simple design and does not tend to instability in operational performance.
The solution according to the invention resides in providing a balancing piston that is arranged firmly on an axially fixed shaft for rotation with radial play. A porting ring which can move axially between the balancing piston and a housing bore is sealed with respect to the housing bore. An end face of the porting ring and a radial annular projection of the balancing portion form a radial choke through which radial flow occurs. The porting ring and the circumference of the balancing piston also define an annular gap forming an upstream throttle. The outside diameter of the radial choke gap is larger than the diameter of the circumference of the porting ring that cooperates with the housing bore.
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REFERENCES:
patent: 2221225 (1940-11-01), Wels et al.
patent: 4892459 (1990-01-01), Guelich
patent: 5104284 (1992-04-01), Hustak, Jr. et al.
patent: 5312225 (1994-05-01), Lorenzen
patent: 5531564 (1996-07-01), Anttonen et al.
patent: 5540546 (1996-07-01), Bouricet

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