Abstrict A flexible membrane variable orifice fluid flow meter which comprises
a body, having a fluid conducting passageway therethrough, where
the passageway has a first lateral width and second lateral width,
and where the second lateral width is greater than the first, a
backing bracket having a flat underside disposed within the second
lateral width portion of the passageway perpendicularly to the direction
of fluid flow and positioned so as to be superimposed over the first
lateral width portion of the passageway, where the backing bracket
has a lateral width less than the second lateral width but greater
than the first lateral width of the passageway, a flexible membrane
having head and toe ends, disposed between the flat underside of
the backing bracket and the first lateral width portion of the passageway,
and secured at its head end between the backing bracket and the
body so that under conditions of zero fluid flow rate, the membrane
obstructs the passageway across the second lateral width thereof,
and differential pressure sensing ports disposed respectively in
the first and second width portions of the passageway.
Claims We claim:
1. A variable orifice fluid flow meter, comprising,
a body having first and second differentially laterally dimensioned
fluid conduits therethrough and wherein the conduits are interconnected
at a plane perpendicular to the direction of fluid flow,
a backing bracket having a flat underside disposed within the second
fluid conduit and over and parallel to the plane interconnecting
with the first fluid conduit, wherein the backing bracket has a
width less than the width of the second conduit and greater than
the width of the first conduit,
a flexible membrane having head and toe ends and disposed between
the flat underside of the backing bracket and the first conduit
and secured at its head end between the backing bracket and the
body so that under conditions of zero fluid flow rate, the membrane
obstructs the fluids flow through the first conduit, and
differential pressure sensing means disposed respectively in the
first and second fluid conduits.
2. The combination of claim 1 and further including,
first adjustable abutment means carried by the backing bracket
and positioned over the toe end of the membrane to selectively limit
the distance which the toe end of the membrane can travel in the
direction of the fluid flow.
3. The combination of claim 2 and further including,
second adjustable abutment means carried by the backing bracket
and positioned over the membrane intermediate its head and toe ends
to selectively limit the distance which the central portion of the
membrane can travel in the direction of the fluid flow.
Description The present invention relates generally to measurement of fluid
flow and more particularly to that type of such device known as
an orifice meter.
BACKGROUND
Orifice meters, using piezometric methods to determine the differential
head across a fixed orifice a conduit though which a fluid flows
are well known in the prior art. A fixed orifice flow meter, however,
has a very narrow range of flow rates over which accuracy of measurement
can be maintained. If the orifice is small enough to provide good
resolution of head differentials at low flow rates, the orifice
will restrict much higher flow rates and produce erroneous high
flow rate measurement. On the other hand, if the orifice is large
enough to accommodate large flow rates there will be poor resolution
of pressure differentials at low flow rates and consequent inaccurate
measurements.
It is therefore the primary object of the present invention to
provide a variable area orifice associated with the generation of
differential pressure signal for use as a fluid flow meter.
A second objective of the invention is provide flow measuring apparatus
having substantial pressure differentials across the measuring orifice
for a wide range of rates of flow in order to achieve accurate measurements
at both high and low flow rates.
THE DRAWINGS
FIG. 1 is a longitudinal cross sectional view of the flow meter
of the present invention, taken along lines 1--1 of FIG. 3 showing
an input body and a superimposed output body the variable orifice
device of the present invention interposed therebetween. The membrane
of the variable orifice device is shown in a fluid flow state where
the flowing fluid pressure is sufficient to flex the membrane into
a bow shape, as shown.
FIG. 2 is a cross sectional view taken along lines 2--2 of FIG.
1.
FIG. 3 is a top view of the input body and the attached backing
plate which secures a flexible membrane to cover an opening in the
top of the input body.
DETAILED DESCRIPTION
In the preferred embodiment of the invention the flowmeter 2 comprises
a body having a bottom half 4 and a superimposed upper half 6. A
fluid carrying passageway traverses the bottom and top halves of
the body with variable orifice 8 in the passageway. The flow direction
of the fluid through the meter 2 is indicated by the large arrows
within the main fluid conduits 9 and 11. The fluid being measured
can be either in the liquid or gaseous phase.
Referring now to the drawings, and initially to FIG. 1 thereof,
the bottom half 4 of the body of the flow meter comprises a solid
block structure having a bore 9 threaded at its entry end for receiving
a mating threaded end of a fluid conducting pipe or conduit (not
shown). The bore 9 terminates in an aperture 12 in the ceiling 13
of the bore 9. The aperture 12 is, by the apparatus of this invention,
transformed into a variable area orifice by the pressure responsive
movement of a normally flat, flexible membrane, or reed, 15 which
is positioned to cover the aperture 12 when fluid flow pressure
is not present. In the preferred form of the invention, the membrane
15 is elongated in its shape, having head and toe ends. The head
end 16 of the membrane 15 is clamped in place between the bottom
half of the body 4 and a first end of a backing bracket 17. The
bracket has a relieved center portion 19 on its flat underside into
which the membrane may rise, bow or flex, when exposed to flowing
fluid pressure from its underside, that is the side next to the
aperture. The first end of the backing bracket is attached to the
bottom half 4 by a screw or similar fastener 21 which, together
with screw fastener 24 at its second end, holds the backing bracket
17 to the bottom half 4. The toe end 18 of the membrane, on the
other side of the aperture 12 from its head end 16 is relatively
free, being constrained only against vertical movement beyond a
selective limit by the lower end of a low flow adjustment bolt 23.
The bolt 23 is threaded into and carried by the backing bracket
and is positioned over the toe end 18 of the membrane 15. A maximum
flow adjustment bolt 26 is also threaded through and carried by
the backing bracket 17. It is positioned over the membrane 15 at
a location along the length of the membrane which is over the aperture
12. In operation, the quiescent, or no fluid pressure, position
of the membrane is to lie flat against the surface surrounding the
aperture 12 effectively closing the aperture. When fluid pressure
is first felt in the bore 9 the toe end 18 of the membrane is lifted
off of the surface, creating a space around the sides of the membrane
through which the fluid can flow from the aperture 12. However,
the toe end of the membrane can lift away from the apertured surface
only until it comes in contact with the low flow adjustment bolt
23. The area of opening of the orifice at the position when the
membrane first contacts the low flow adjustment bolt defines the
area of the smallest orifice in the range of orifice sizes to be
allowed by the device of the present invention. As inflowing fluid
pressure continues to increase in the bore 9 the membrane begins
to flex in its center portion, both ends being restrained against
further upward motion. The purpose of the maximum flow adjustment
bolt 26 is to limit the bend or flex of the membrane, as shown in
FIG. 1 in order to establish a maximum orifice size for the flow
meter.
The output portion 6 of the flow meter body contains an interior
portion 11 which communicates through a threaded coupling with a
fluid output pipe or conduit (not shown). In the embodiment shown,
the upper half 6 of the body is sized and dimensioned to fit onto
the top surface of the bottom half 4 of the body and be secured
thereto by a series of bolts 30. In an alternative embodiment, a
body containing the input and output passages 9 and 11 could obviously
be a single piece. The side walls 32 and 33 of the interior cavity
11 in the upper half 6 of the body are dimensioned so that fluid
passage spaces 35 exist between those side walls and the sides of
the membrane and its overlying backing bracket.
A fluid input pressure measuring port 41 located in the bore 9
of the bottom half 4 measures the pressure of the input fluid in
a customary manner. Similarly, a fluid output pressure measuring
port 43 is located in the cavity 11 of the upper half 6 for measuring
the pressure of the output fluid. These fluid pressures are communicated
to a differential pressure measuring device, known in the prior
art (not shown). The pressure drop across the variable orifice structure
8 as measured by the differential pressure measuring apparatus,
is, with other known factors, determinative of the rate of fluid
flow through the aperture 12 in accordance with known fluid flow
measuring principles.
In operation, the objects of this invention are accomplished by
the flexing of the membrane 15 as a function of the fluid pressure
changes, to vary the size of the fixed aperture 12 from a minimum
to a maximum sized effective orifice. When the membrane 15 is not
subject to fluid pressure, it lies flat against the top surface
of the bottom half 4 and covers the aperture 12. As the input fluid
pressure becomes effective, the free toe end of the membrane 15
will lift off the bottom half 4 until the toe end contacts the low
flow adjustment screw 23 and upon application of greater pressure
the membrane will bow accordingly, uncovering a greater area of
the aperture 12 and increasing the effective size of the orifice.
As the membrane flexes upwardly the aperture 12 will increasingly
lose its cover and fluid will pass through the aperture and bilaterally
around the sides of the membrane into the spaces 35 and then into
the output cavity 11. In this structure the orifice is actually
defined as the area of the aperture 12 reduced to the area of the
bilateral openings between the flexed membrane and the top surface
of the bottom half 4. Thus for maximum flows, where the fluid pressure
is greatest, the orifice will present its maximum area and the pressure
drop across the orifice will be smaller. When flow rates and fluid
pressure are low the combination of the membrane and the aperture
12 will present a smaller area orifice, providing a larger pressure
drop thereacross.
While the preferred form of the invention has been described in
terms of a flow meter body having fluid conducting conduits or cavities
therein, it is well within the scope and intent of the invention
that the variable orifice device could be as simple as a body having
an opening and a covering membrane which is insertable as a unit
into a fluid passageway. The body is sealed within the passageway
so that flowing fluid can pass only through the opening in the body.
Pressure differential sensing apparatus would then be arranged to
sense the pressures in the fluid on both sides of the inserted body.
It is apparent from the foregoing description and the accompanying
drawings that the orifice, across which the pressure drop is measured,
is changed in its area to accommodate both low and high flows, in
accordance with the objects of the invention. The membrane can be
sized and adjusted by the low and maximum flow screws to provide
good flow measurement results for a very wide range of flows. The
construction is simple and cost effective and has a predictable
temperature reaction that is easily compensated for.
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