Measuring and testing – Volume or rate of flow – Expansible chamber
Patent
1993-10-04
1995-02-28
Chilcot, Jr., Richard E.
Measuring and testing
Volume or rate of flow
Expansible chamber
222 59, G01F 1104, 222, 222
Patent
active
053926480
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a gauge for liquid flow measurement and in particular to a gauge for detecting when a pre-determined volume of liquid has passed through the gauge.
Background of the Invention
Certain liquid delivery systems require a predetermined volume of liquid to be repeatedly delivered. There are many known metering devices for measuring volumes of beverages, particularly beer and lager, and other liquids such as chemicals etc., which comprise pressure driven constant displacement pumps in which one side of a sealed piston in a cylinder is pressurized to push the piston which in turn pushes liquid out the cylinder from the other side of the piston. Valves are used to interchange the high and low pressure sides with respect to the piston such that two way reciprocating metering and dispensing of pre-determined volumes can occur. The accuracy of the volume dispensed depends on the ability to control the length of the stroke of the piston and there are a variety of means to detect and control the piston end stop position. Examples of such metering devices are disclosed, for example, in British Patent Specifications Nos. 2233084, 2126193, 2112177, 2089767, 1591881, 1432741 and 1250451.
A further liquid delivery system which requires a pre-determined volume of liquid to be repeatedly delivered is an inhaler which delivers metered doses of a liquid in the form of a dispersion of fine droplets in air, more particularly droplets of a drug solution or suspension for inhalation. The inhaler may comprise a reservoir of drug solution or suspension from which a metered volume is supplied to an aerosol generator to create the dispersion of droplets for delivery to the patient. Such inhalers are disclosed and claimed in our co-pending PCT Patent Publication No. WO92/11050.
Summary of the Invention
The present invention provides a gauge for liquid measurement which is capable of repeatedly measuring a pre-determined volume of liquid or suspension.
According to the present invention there is provided a gauge for measuring a pre-determined volume of liquid flowing therethrough comprising a conduit for said liquid and a slug positioned within said conduit, the slug having substantially neutral buoyancy in the liquid to be measured and being constructed and arranged such that it will move along the conduit at substantially the same rate as liquid flowing therein and is capable of being moved through the conduit with no net flow of liquid, the conduit comprising a constraint system defining a length of the conduit within which the slug is free to move, the gauge comprising detection means capable of detecting when the slug has moved a predetermined distance within the conduit.
The gauge of the invention provides a simple effective means of measuring a pre-determined volume of liquid passing through a conduit. The gauge may be used to generate a signal when the pre-determined volume has been dispensed, which signal may be employed to activate control means used to control the liquid dispensing system. For example, the control means may deactivate a pump upon receiving a signal from the gauge and thereafter may cause the gauge to be reset.
The gauge essentially comprises a conduit which may conveniently be in the form of a tube of metal, plastics or glass. The conduit contains a slug which has a net density approximately matched to that of the liquid to be measured so that the slug has substantially neutral buoyancy in the liquid. The slug is preferably dimensioned such that it is slightly smaller than the bore of the tube and will move along the tube at the same rate as the liquid flow therein. The gauge includes means to detect the slug when the slug has moved a predetermined distance. Thus, during the distance moved to the detection point a volume of liquid approximately equivalent to: (the distance moved by the slug x cross-sectional area of bore of tube) will have been dispensed. Thus, by selecting suitable dimensions for the bore of the tube and the distance to be moved by the s
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Chilcot Jr. Richard E.
Griswold Gary L.
Hulse Dale E.
Kirn Walter N.
Minnesota Mining and Manufacturing Company
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