Seal device for a fluid machine

Abstract

A seal device 25B has a wear-ring 31 fixed to a casing 2 of a centrifugal pump and a floating ring 32. An annular gap 36 between an inner peripheral surface of a through bore 32a formed in the floating ring 32 and an outer peripheral surface of a mouth ring portion 19 of an impeller 5B is smaller than an annular gap 35 between an inner peripheral surface of a through bore 31a formed in the wear-ring 31 and the outer peripheral surface of the mouth ring portion 19. Fluid leakage from a high pressure area to a low pressure area in the casing 2 through the gaps is prevented.

Description

BACKGROUND OF THE INVENTION[0001]The present invention relates to a seal device for a fluid machine (turbo machine) such as a pump, turbine, compressor, and gas turbine. Particularly, the present invention relates to a seal device for preventing leakage of a fluid from a high pressure area to a low pressure area in a casing of the fluid machine through a gap between the casing and a rotor disposed in the casing.[0002]An example of a seal device installed between a casing and a rotor such as a main shaft or an impeller of a fluid machine is disclosed in Japanese Utility Model Application Laid-open Publication No. 6-018694. The seal device uses a wear-ring. Specifically, a gap is formed between an inner peripheral surface of the wear-ring fixed to the casing and an outer peripheral surface of the rotor, and a size of the gap is set to as small as possible, thereby preventing the fluid leakage from a high pressure side to a low pressure side via the gap.[0003]However, the conventional ...

AI Technical Summary

Benefits of technology

The present invention provides a seal device for preventing leakage of fluid from a high pressure area to a low pressure area in a fluid machine through a gap between the casing and a rotor disposed in the casing. The device can minimize the amount of leakage, reduce vibrations, prevent seizure, and inhibit wear and cavitation with a relatively simple structure and easy manufacturing and maintenance. The device includes a main ring and a thin auxiliary ring with separate elements, and the gap between the inner peripheral wall of the main ring and the outer peripheral surface of the rotor is set narrower than the gap between the inner peripheral wall of the auxiliary ring and the outer peripheral surface of the rotor to minimize the amount of fluid leakage. The thin auxiliary ring is easily assembled to the main ring and can be easily removed and replaced. The device can be easily manufactured and maintained.

Problems solved by technology

First, where the gap between rotor and the inner peripheral surface of the wear-ring is set too small for reducing the fluid leakage, assemble of the wear-ring and rotor is impractical. This is caused by size errors or assembling errors inevitably occur even if the wear-ring and rotor are machined with highly precise machining accuracy. Therefore, the gap size needs to be set to a certain level with consideration for assembling, thereby placing limitation on possible leak reduction.

Further, vibrations occur due to contact of the rotor and wear-ring during operation of the fluid machine, and these vibrations can cause seizure.

However, because the lining wears off due to contact of the rotor and wear-ring, long term operation of the fluid machine can cause exposure of the metal material covered by the lining which results in seizure.

The fluid flowing with the high flow rate passing through the gap causes wear of the wear-ring In addition, in a vicinity of an exit at the lower pressure side of the gap, rapid pressure drop due to remarkably increased flow rate can cause cavitation by which vibrations and wearing are occurred.

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