Measuring and testing – Volume or rate of flow – System
Patent
1982-01-25
1984-02-07
Ruehl, Charles A.
Measuring and testing
Volume or rate of flow
System
G01F 700
Patent
active
044295715
DESCRIPTION:
BRIEF SUMMARY
This invention relates to the measurement of liquid flow in closed conduits, where the flow is subject to a wide range of variations.
BACKGROUND
Compound liquid flow meters have parallel flow paths, one of which includes a turbine meter accurate over a wide range of relatively high flow rates, but inaccurate below a known minimum rate. The other flow path includes a meter accurate at low flow rates, but having a narrow range with a low maximum rate of flow greater than the minimum flow rate of the turbine meter. It is essential that the flow path through the turbine meter be closed by a valve during the low range of flow rates where that meter is inaccurate. It has previously been considered necessary to have the valve quick-acting in response to the rate of flow, so that it opens quickly when the flow rate exceeds the minimum accurate flow rate of the turbine meter, and so that it closes quickly when the flow rate falls below that minimum.
Many quick-acting valve mechanisms have been proposed in the prior art. See for example Masson et al. U.S. Pat. Nos. 3,677,084 and Pelt, 4,100,800. The prior art quick-acting valve mechanisms are complex. Masson et al. uses a combined cam and toggle mechanism. Pelt uses a complex mechanism involving two cams and an inclined plane. The prior art compound meters including quick-acting valve mechanisms have reduced accuracy during the crossover range of flows during which the valve is opening or closing. This lack of accuracy is recognized in the standard for such meters published by The American Water Works Association and identified as their Standard C-702-78. That standard allows compound meters to have a minimum accuracy as low as 90% in the crossover range where the valve is opening or closing, but requires that the total crossover range of flow rates where accuracy is below 97% be limited (e.g., 20 gals. per min. for a 3 in. meter).
BRIEF SUMMARY OF THE INVENTION
This compound liquid flow meter has a principal flow path including a wide range turbine meter which is accurate for a range of flows greater than a predetermined minimum flow. The meter also includes a parallel auxiliary flow path through a conventional meter such as a positive displacement meter, which is accurate over a lower range of flow rates. The upper end of that lower range overlaps the low end of the accurate range of flow rates of the turbine meter.
The compound meter includes a casing open along a portion of one side and having an inlet at one end and an outlet at the opposite end. The casing has a transverse wall between the inlet and the outlet, and an aperture in the wall is part of the principal flow path.
A main valve, which is disclosed as a simple poppet valve, controls the flow through the aperture. That valve is mounted on a stem extending through a valve guide which also serves as a retainer for a spring which biases the valve to closed position. When there is no flow through the valve, the total pressure difference between the upstream and downstream sides of the compound meter acts on the valve in a valve-opening direction. The valve assembly including the valve, stem, guide and spring, is mounted on the downstream side of-the transverse wall in the casing.
A cover for the open side of the casing supports the turbine meter within the casing on the upstream side of the transverse wall. The turbine meter must be one having a highly accurate characteristic, i.e., one which attains a high and constant accuracy at a rate of flow just slightly above the minimum rate which starts rotation of the turbine. The lower range meter is supported by the cover, which contains the parallel flow path.
The auxiliary flow path must include a fixed orifice of carefully selected size, which determines the pressure drop across the compound meter when the main valve is closed, and hence determines the rate of flow at which the main valve starts to open.
The auxiliary flow path may also include a secondary flow responsive valve which is biased open and closes in response to a predetermined pressure diff
REFERENCES:
patent: 3203238 (1965-08-01), Whittaker et al.
patent: 3395578 (1968-08-01), Simonds, Jr.
patent: 4100799 (1978-07-01), Bradham et al.
Harris Rodney G.
Karjalainen William G.
Kullmann Donald J.
Neptune Water Meter Company
Ruehl Charles A.
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