Floating-ring seal

Details Floating-ring seal Floating-ring seal

1994-10-07

1996-05-21

Cummings, Scott W.

Seal for a joint or juncture

Seal between relatively movable parts

Relatively rotatable radially extending sealing face member

277174, 277176, 277 57, F16J 15447

Patent

active

055182569

DESCRIPTION:

BRIEF SUMMARY
The invention relates to a floating-ring seal in accordance with the generic part of the main claim.
Centrifugal pumps with separate driving motors have at least one shaft seal that is intended to help prevent the discharge of the pumping medium from the interior space of the pump along the shaft. Additional sealing systems are provided inside the pump to limit internal leakage currents.
The usual rotating mechanical seals used as shaft seals in centrifugal pumps are limited to applications with running speeds less than 50 m/sec. Beyond that speed range the serviceable life is very unsatisfactory. Therefore, for more rapidly rotating centrifugal pumps, rigid, non-contact choke gaps or so-called floating-ring seals have gained acceptance. However, both seal designs have the disadvantage of a high loss of efficiency. Moreover, attempts to construct choke gaps between a turning and a rotating part that are as narrow as possible are subject to technical limitations. For example, multistage centrifugal pumps with a horizontal shaft that are used to convey hot media are subject to operating conditions during which blocking of the rotor can occur as a result of excessively-narrow impeller choke gaps when there are distortions of the casing or rotor. To avoid that problem, very expensive structural measures are known from prior art. The problem can be avoided by using large choke gaps, but that results in significant losses of efficiency.
A floating-ring seal for shaft seals of the type described above is known from U.S. Pat. No. 3 213 798, in which floating rings are arranged in separate chambers and surround the shaft with clearance. In that fashion a choke gap is formed between the interior diameter of the floating rings and the shaft, the effect of which is relatively unreliable due to the multiplicity of choke gaps. However because of the effect of pressure, one face of the sealing rings rubs against their chamber wall, so that at high speeds there are significant abrasion problems. U.S. Pat. No. 3 779 667 shows another floating ring that is arranged with clearance in its chamber and used as an impeller split ring. Due to the pressure ratios inside the pump, the face of the floating ring that is opposite the pressure is pressed against the associated surface of the casing wall. Therefore, the non-contact mobility when at rest is limited during operation. This approach may be feasible for small circumferential speeds, but it fails at higher circumferential speeds and greater radial rotor vibrations.
The aim of the invention is to develop a sealing system for centrifugal pumps that are driven at a high speed, which with low leakage currents have a long serviceable life and are not sensitive to rotor distortions and vibrations.
That aim is achieved through the recitations contained in the generic part of the main claim. The principle of the floating ring that moves freely and without contact during operation can be implemented uniformly between the rotating and stationary pump components, on which pressure differences are produced. Thanks to the regulating gaps, each floating ring arranges itself without contact in the chamber enclosing it. Because it does not come into contact, it can be used at very high circumferential speeds. The two walls disposed at an angle to each other and rotating at the speed of the drive, as well as the stationary walls opposite those walls, cause the floating ring to rotate inside its chamber at a moderate speed that corresponds to approximately half of the speed of the drive. Consequently, during the worst cases of starting up or turning off the motor, any potential contact will occur at only a maximum of half the speed of the drive. Compared with floating rings of prior art, in which the relative speed between the stationary and rotating parts corresponds to the speed of the drive, the abrasion resistance of the floating rings in accordance with the invention is extremely high and enables them to be used without difficulty at high speed ranges.
The embodiments described in claims

REFERENCES:
patent: 2912265 (1959-11-01), Brummer
patent: 3046648 (1962-07-01), Kelly
patent: 3476397 (1969-11-01), Thoren et al.
patent: 3720419 (1973-03-01), Adelizzi
patent: 4199152 (1980-04-01), Catterfeld
patent: 4643639 (1987-02-01), Caine
patent: 4685684 (1987-08-01), Ballard
patent: 5028054 (1991-07-01), Peach
patent: 5037114 (1991-08-01), Gray

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