Single Jet Wet Type Water Meter systems
The present invention relates to a meter for liquid, in particular water, of the type having a single jet.
More precisely the present invention relates to a liquid meter of this type having improved sensitivity, in particular at low flow rates. Water meter.
BACKGROUND OF THE INVENTION
Water meters may be divided into two large categories: volumetric meters and speed meters. Volumetric meters, e.g. meters having a rotating piston, enable very good sensitivity to be obtained at low flow rates, but their manufacturing cost is relatively high because they require highly accurate machining.
Speed meters may be sub-divided into Woltman type meters in which liquid flow rotates a propeller whose axis of rotation is parallel to the direction of liquid flow, and jet meters in which the liquid to be measured enters a measurement chamber perpendicularly to the axis of rotation of a turbine.
Woltman type meters are well adapted to metering liquids flowing in large bore pipework (typically not less than 80 mm in diameter) whereas jet type meters are used in conjunction with medium and small diameter ducts.
Jet type meters may further be sub-divided into single jet meters and multiple jet meters. In multiple jet meters the water inlet pipework opens out into an annular feed chamber. The measuring chamber in which the turbine is mounted is separated from the feed chamber by a cylindrical wall having orifices therethrough. The measurement chamber is thus fed by a plurality of jets created by these orifices, which jets cause the turbine to rotate. Multiple jet meters have good sensitivity, but their manufacturing cost is relatively high because of their relatively complex structure.
In single jet meters, the upstream pipework opens directly into the measuring chamber via an injector. The structure of such meters is thus much simpler and their cost is reduced. However, meters of this type generally suffer from mediocre sensitivity at low flow rates, and they can only be used as subsidiary meters because of their mediocre measuring qualities.
French published patent specification No. 2 336 666 seeks to remedy this drawback, i.e. to provide a single jet meter which has adequate measuring qualities to be used as a main or principal meter, by using a special method of pivoting the turbine to limit the friction torque at low flow rates, i.e. at low speeds of turbine rotation. According to that patent specification, the bottom end of the turbine¡¯s vertical shaft is terminated by a fine point, while its top end is terminated by a flat abutment surface.
At low flow rates, the shaft is supported by its fine point engaging a jewel which ensures sensitivity because of the low friction torque. As the flow rate increases, the bottom point lifts progressively out from the jewel until the turbine is completely lifted and has its top abutment surface pressing against a thrust bearing of suitable dimensions for the thrust involved. The turbine is lifted because of a vertical component in the resultant of the forces applied to the turbine. This component is increased by the presence of radial ribs projecting from the bottom of the measuring chamber.
Although this solution serves to reduce the friction torque at low flow rates, and thus to improve meter sensitivity in this operating range, it nevertheless suffers from the drawback of requiring a strong top bearing capable of absorbing the axial thrust from the turbine when operating at high speeds of rotation.
An object of the invention is to provide a single jet meter in which the turbine bearings are further improved so as to enable good sensitivity, particularly at low flow rates, while retaining low manufacturing costs compatible with mass production.
SUMMARY OF THE INVENTION
In a first aspect the present invention provides a meter comprising: a cylindrical measuring chamber having first and second end walls perpendicular to the axis of said chamber; an injector and an ejector in communication with said measuring chamber; a turbine having a hub and plurality of blades fixed to said hub, said hub having first and second end faces disposed opposite said first and second end walls respectively; means for guiding the said turbine in rotation about the axis of said chamber; a set of radiating ribs fixed to said first end wall and projecting into said chamber; the meter including the improvement whereby it further comprises an assembly constituting an axial stop disposed adjacent said first end face and constituted by a pivot having a tapering point and an abutment which is in contact with said point when the liquid flow rate is zero, means for subjecting said second end face to a pressure reduction effect produced by rotation of said liquid in said chamber, and means for protecting said first end face from said reduced pressure effect at low speeds of rotation of said turbine, in such a manner that the turbine moves axially to take said point out of contact with said abutment, and to subject said first end face to said pressure reduction phenomenon from a given axial displacement of said turbine, such that said turbine is fixed axially under the reduced pressure effect which is applied to both of said end faces.
It can thus be seen that the axial position of the turbine is regulated in such a manner that the turbine pivot point is in contact with the abutment at low speeds of rotation, that the turbine moves progressively away from said contact up to a given distance with increasing speed; and that the turbine then occupies a stable axial position above a given speed without requiring an axial end stop.
In a second aspect the present invention provides a meter comprising: a cylindrical measuring chamber having first and second end walls perpendicular to the axis of said chamber; an injector and an ejector in communication with said measuring chamber; a turbine having a hub and plurality of blades fixed to said hub, said hub having first and second end faces disposed opposite said first and second end walls respectively; means for guiding the said turbine in rotation about the axis of said chamber; an assembly constituting an axial stop disposed in the vicinity of said first end face and formed by a pivot having a point and an abutment which is in contact with said point when the liquid flow rate is zero; and a set of radiating ribs fixed to the first end wall of the measuring chamber, said ribs being suitable at low flow rates of the liquid to be measured for generating vortex phenomena in the spaces separating said ribs in such a manner that said vortex phenomena creates a hydraulic plug in the vicinity of said first end wall such that the zone left free for laminar flow between the meter turbine and said hydraulic plug extends in the direction of said axis of rotation over a length which is not greater than the distance in the same direction between said ribs and said turbine.
