Shrouded flowmeter turbine and improved fluid flowmeter using the same

Abstract

A fluid flowmeter, of a type including a housing and a fluid flow measurement assembly rotatable therein which is driven by a turbine, is described in detail to illustrate a limitation on low flow rate operational capability and a related problem of contaminant particle malfunctions. A specific flowmeter used for such illustration is a typical prior art motorless mass flowmeter including a turbine secured to and rotatable with a shaft which in turn rotates a downstream impeller by means of a spring, the impeller being independently supported for rotation, so that relative deflection between the impeller and the shaft is a measure of mass flow rate. To minimize fluid leakage around a peripheral surface of the turbine in proximity to the housing in order to achieve low flow rate operation, while yet avoiding stoppage of the turbine due to contaminant particles being lodged in or near the leakage path, a shroud member is utilized upstream of the turbine which comprises a hollow member of revolution rotatable with the turbine which has a first end secured to the turbine, in a fluid-tight seal, at points radially outward of a plurality of turbine drive means in the turbine and which tapers to a second end, proximate to a fluid inlet opening, to form a rotatable fluid seal with a sealing means surrounding the fluid inlet opening.