Abstrict A fluid flow meter of the variable area flow passage type is provided
wherein the variation in said flow passage area is effected by the
vertical displacement of a control boundary which is supported by
a substantially horizontal annular diaphragm element. Said control
boundary is shaped and sized so that the overall displacement required
for the flow rate range desired is within the stroke capacity delivered
by the total, up and down, free flexing action of said diaphragm
element, thereby achieving substantially constant differential pressure
operation at a very reasonable value which is due almost entirely
to gravity. The resulting unit is very compact and stable and is
characterized by very smooth linear response between vertical displacement
and fluid flow rate. Said vertical displacement can be measured
by various means but is preferably transduced to an equally linear,
smooth and steady electrical signal by a direct connection with
a specially adapted differential transformer.
Claims Having described my invention together with preferred embodiments
thereof, what is claimed is:
1. A fluid flow measuring device characterized by a highly linear
response and a substantially constant differential pressure operation
comprising a main casing; a substantially horizontal partition member
peripherally attached to the lateral walls of said casing in a fluid
tight manner, said partition member having a large open area in
the middle thereof and being sufficiently flexible to present negligible
resistance to measurable vertical motion of its central portion
in both directions from the horizontal; a fluid inlet into said
casing below the level of said peripheral attachment of said partition
member and a fluid outlet from said casing above said level; a rigid,
symmetrically shaped fluid flow control element symmetrically mounted
on the central portion of said partition member; rigidly mounted
on said casing in uniform directly opposed alignment beneath said
element a cooperatively designed fluid flow control element positioned
so that it is substantially below the upper control element when
said partition member is horizontal but within full contact reach
of same upon deflection of the central portion of said partition
as permitted by its said negligible resistance motion capability;
and means for measuring said vertical motion upwards from the point
of contact between the respective fluid flow control elements.
2. The device of claim 1 wherein said means comprises an indicator
rod rigidly mounted from said partition member.
3. The device of claim 2 wherein said indicator rod extends beyond
the main casing and an auxiliary enclosure is provided on said casing
at that point having means thereon for visually determining vertical
positioning of said rod.
4. The device of claim 2 wherein an electrical transducer or signalling
device is provided immediately outside of said main casing and said
indicator rod is coupled to said transducer or device.
5. The device of claim 4 wherein said transducer is a differential
transformer and said indicator rod is rigidly connected to the core
of said transformer.
6. The device of claim 1 wherein said partition member comprises
a thin diaphragm.
7. The device of claim 6 wherein said diaphragm has at least one
concentric convolution formed in the outer portion thereof and said
partition member also includes thick heavy annular plate members
mounted on either side of said diaphragm between said concentric
convolution and the open area in the middle thereof.
8. The device of claim 7 wherein said measuring means comprises
an indicator rod rigidly mounted concentrically from said partition
member by means of a rigid connection to one of said plate members.
9. A rugged, compact flow meter of the variable area orifice type
which is especially suited for accurately measuring the flow rates
of gases at low pressures due to its highly linear response characteristics
and constant differential pressure over widely varying flow rates
comprising a main casing; a substantially horizontal diaphragm extending
from the lateral walls of said casing and having a large non-controlling
open area in the central portion thereof, thus partitioning said
casing into an upper and a lower section with intercommunication
therebetween solely via said open area, the central portion of said
diaphragm being capable of limited but measurable stress free motion
both above and below the horizontal; a fluid inlet into said lower
section and a fluid outlet from said upper section; at least one
relatively heavy annular plate member concentrically mounted on
said diaphragm and having a rigid, symmetrically shaped fluid flow
control element thereon in fluid tight communication with said open
area; rigidly mounted on the floor of said casing in uniform symmetrical
alignment with and subadjacent to said control element, a directly
opposed fluid flow control element positioned so that said opposed
fluid flow conrol elements contact each other at a point when the
central portion of said diaphragm is deflected downwards a substantial
distance within the limit of its stress free motion; and means for
determining the vertical displacement of said central portion upwardly
from said point of contact.
10. A flow meter as described in claim 9 wherein said diaphragm
has at least one concentric convolution in the outer portion thereof.
11. A flow meter as described in claim 9 wherein said means comprises
a vertical, rigid indicator rod supported from said diaphragm-mounted
heavy plate member.
12. A flow meter as described in claim 11 wherein said indicator
rod extends beyond the main casing and an auxiliary enclosure is
provided on said casing at that point having means thereon for visually
determining said vertical displacement of said central portion.
13. A flow meter as described in claim 11 wherein a differential
transformer type of electrical transducer having an iron core is
provided immediately outside of said main casing and said indicator
rod is connected to said iron core.
14. A flow meter as described in claim 13 wherein said differential
transformer has a dual secondary winding providing a push-pull type
of reinforced electrical signal in response to vertical displacement
of said iron core from its null or no flow position.
15. The flow meter of claim 9 wherein said fluid flow control element
on said plate member is in the form of a collar or rim extending
downwardly from the bottom portion of said member.
16. The flow meter of claim 15 wherein said downwardly extending
collar or rim tapers to a uniform thin edge at the bottom.
Description BACKGROUND OF THE INVENTION
This invention relates to fluid flow meters of the constant differential
pressure type wherein a movable element is provided which, in automatic
response to changes in fluid flow rate, effects corresponding changes
in cross-sectional area of the minimum flow passage thereof. The
flow meter of my invention is especially adapted for accurately
measuring gas flows over a wide range of rates while maintaining
a highly linear relationship which can be extended readily to a
cooperative electrically transduced indicator system of closely
matched linear responsiveness, if desired.
Over the years considerable effort has been directed toward improving
variable area type flow meters to make them more stable and reliable
and more nearly linear and accurate over a wide range of flow rates.
One of the most common forms of apparatus developed in this field
is the so-called rotameter, a device in which a generally roundish
float element is lifted inside of an upwardly expanding tapered
tube to heights directly dependent upon the fluid flow rates therethrough.
Due to their simplicity and responsiveness, rotameters are very
popular but are too fragile and erratic for many applications due
to such problems as float bounce, mechanical resonance and uncertain
or variable alignments.
Most of the more rugged variable area flow meters developed to
date have movable elements which are either inherently stiff or
separately spring biased, or else encumbered with sufficient frictional
effects to dampen their responsiveness and prevent true linearity
of the position vs. flow rate relationship. Examples of this type
of flow meter in which the movable element is deliberately counterbiased
with a back up spring are disclosed in U.S. Pat. No. 3234790 to
Ekstrom and U.S. Pat. No. 1416220 to Long et al. On the other
hand, Ongaro in U.S. Pat. No. 3218853 has advocated the use of
a primarily gravity opposed movable element in such flow meters
provided said movable element is vertically aligned. However, said
patentee also points out the extreme difficulty of eliminating mechanical
interferences and frictional resistances in any such device which
is capable of durable service over a reasonable range of operating
conditions.
The primary object of this present invention is to provide an essentially
constant differential pressure, variable area flow metering device
in which the movable element is truly gravity opposed and mechanical
friction is effectively eliminated thereby achieving a very smooth
linear response between fluid flow rate and displacement of the
movable element. It is further object of my invention to provide
such a device which is durable and can be used continuously and/or
repeatedly to deliver a smoothly linear and unchanging mechanical
response to flow rates varying over a wide range (e.g. 10/1 or higher
ratios). It is also one of my objects to provide such an apparatus
which is compact and simple to use and operate.
A secondary object of this invention is to provide a directly coupled
electric transducer which has a smoothly linear output closely matched
to the mechanical displacement of the movable element in the variable
area metering device over its full operating stroke. Finally, it
is a special object of my invention to provide throughout my apparatus
the capability of using corrosion resistant materials of construction
so that it can be used to measure the flow rates of such aggressive
gases as chlorine, oxides of nitrogen or sulfur, anhydrous ammonia
etc.
Further objects and advantages of this invention will be apparent
from the following description including exemplary and preferred
embodiments as illustrated in the accompanying drawings, wherein:
FIG. 1 is a cross-sectional elevation along the center line of
a basic flow meter constructed in accordance with the present invention;
FIG. 2 is a top sectional view taken along line 2--2 of FIG. 1;
FIG. 3 is a cross-sectional elevation along the center line of
another embodiment of flow meter operating on the same general principles
and especially suited for measuring small flow rates;
FIG. 4 is a top sectional view taken along line 4--4 of FIG. 3;
FIG. 5 is a cross-sectional elevation along the center line of
another embodiment of my invention in which a preferred type of
electrical transducer is cooperatively integrated with the basic
mechanical elements of the flow meter;
FIG. 6 is a top sectional view taken along line 6--6 of FIG. 5;
and
FIG. 7 is a sectional view taken in the opposite direction along
line 7--7 of FIG. 5.
Referring now in detail to FIGS. 1 and 2 the main housing 10 of
the meter encloses a generally cylindrical space 12 which is transversely
separated into upper and lower portions by means of thin, free flexing
partition member or flexible diaphragm 14. The housing 10 is also
provided with fluid inlet opening 16 into the lower portion of space
12 and fluid outlet passage 18 from the upper portion of space 12.
A large opening 20 is provided in the central area of partitioning
diaphragm 14 in order to permit fluid to pass from lower to upper
sections of space 12. Also, concentric convolution 22 is formed
in the outer portion of diaphragm 14 in order to assure sufficient
mechanically unrestrained up and down movement of the inner portions
thereof to give measurable changes in vertical position which are
accurately indicative of variations in fluid flow over useful ranges,
such as maximum to minimum ratios of about 10/1.
Concentrically mounted on diaphragm 14 to the inside of convolution
22 are relatively thick blocks or plate members 24 and 26 the central
areas of which are also open so as not to interfere with the flow
of fluid up through opening 20. The lowest part of lower plate member
26 is shaped in the form of a downwardly extending concentric collar
or rim 28. This rim 28 is tapered to a precise uniform thin edge
at the bottom in order to provide part of the limiting surface for
the controlling fluid flow passage of the meter. The opposing surface
for the limiting or controlling flow passage is provided by the
horizontal upper face 30 of plug 32 which is mounted in the base
of housing 10 by means of threaded opening 34 using a sealing O-ring
element 36 so that upper face 30 just contacts the lower edge of
rim 28 under stress free, gravity induced deflection of diaphragm
14 from its neutral position. It will be seen that the controlling
flow passage thus defined between rim 28 and plug face 30 takes
the form of a cylindrically shaped slot, the depth and cross-sectional
area of which will increase in direct correspondence with the upward
travel of plates 24 and 26 which is permitted without mechanical
restraint by reversing the downward deflection of diaphragm 14 back
to its neutral position and beyond into its stress-free upwardly
deflected shape.
A vertical position indicator rod or mast 38 is centrally mounted
on the top side of upper plate member 24 by means of bridge plate
40. Bridge plate 40 has fluid passage openings 42 in the central
area thereof and the entire diaphragm and plate assembly is held
together by bolts 44. Indicator mast 38 extends up into the free
space inside of transparent extension cover 46 sealably mounted
in the head of main housing 10. Suitable gradations 39 are engraved
on the portion of mast 38 which are visible through extension cover
46 so that the vertical position can be read relative to a bench
mark 48.
Since no counterbiasing springs are used in my flow meter and the
total stroke is within the movement permitted by the free up and
down flexure of diaphragm 14 the only significant force opposing
the flow of fluid therethrough is the gravitational pull on the
mass of elements supported by diaphragm 14. Therefore, the differential
pressure across a given meter of my construction will be substantially
constant over a wide range of fluid flow rates. Said mass can be
controlled to some extent by choice of materials, thickness of diaphragm
plates 24 and 26 etc. However, limiting said differential pressure
to a very reasonable value is generally easy because of the rather
extensive effective area of the partitioning diaphragm assembly.
This fact renders my devices ideal for measuring gas flows at low
to ordinary pressures. Even under these sensitive conditions, a
very smooth and steady linear response is achieved between the vertical
movement of mast 38 and corresponding flow rates delivered through
the meter.
In FIGS. 3 and 4 there is depicted another embodiment of my invention
based upon the same operating principle but illustrating some optional
constructional features of specific interest. In this embodiment,
the limiting or controlling flow passage is defined at a position
well within the vertical opening through the diaphragm plate assembly
instead of at the lower rim of the lower plate member as in the
previously described contruction. Specifically, in this case, the
opening through upper diaphragm plate 25 is smaller than the central
openings through diaphragm 14 and lower plate 27 and is shaped as
a precisely tapered, upwardly converging frustoconical section 23
leading to throat section 21 and then diverging rapidly at the top.
Cooperatively aligned with said opening is plug 32 mounted in the
base of housing 10. Concentric extension post 33 on plug 32 extends
vertically up through frustoconical section 23 and is provided with
horizontal shoulder 35 tapered on top so that a thin edged outer
rim is formed thereon the outside diameter of which is slightly
greater than the diameter of throat section 21. Thus, the limiting
flow passage in this device is in the form of an annular slot which
gradually increases in width in direct proportion to the upward
travel of the inner portion of diaphragm 14 under the lifting force
of the flowing fluid.
Also, in this case downwardly concave concentric convolutions 23
are provided on either side of upwardly concave convolution 22 in
diaphragm 14 in order to ensure a somewhat larger mechanically unrestrained
vertical movement or permissible total stroke of the indicator mast
38. The mast 38 of this unit is mounted on top of upper plate 25
by means of concentric, inverted cup shape bracket 41 having large
fluid outlet passages 43 in each lateral quadrant thereof. Four
matching lugs 11 of equal height are provided on the inner floor
of housing 10 providing uniform support for the diaphragm plate
assembly under static conditions while still permitting light contact
of the rim of shoulder 35 with the inner surface of frustoconical
section 23. Tests of devices constructed in accordance with FIGS.
3 and 4 have also shown fully linear responsiveness. Also, because
of the larger stroke provided, reading the indicator to a given
degree of accuracy generally requires less effort.
Attention is next directed to FIGS. 5 6 7 wherein there is illustrated
the integration of the mechanical features of the present invention
with an electrical transducer system of matched linearity so that
the mechanical motion of the indicator rod is translated directly
into a linearly responsive electrical signal which is more easily
and accurately detected, read and/or recorded. Although the mechanical
arrangements and actions of this embodiment are quite similar to
those of FIGS. 1 and 2 a few minor modifications should be noted.
First, in order to provide for larger fluid flow capacities, the
diameter of the thin edged control surface of rim 28 is made considerably
greater and the horizontal floor of main housing 10 itself serves
as the opposing surface of the cylindrical slot under rim 28 which
constitutes the limiting flow passage. Secondly, the upper face
of the lower diaphragm plate 26 is cut away slightly beginning from
a short distance outside the ring of assembly bolts 44 and tapering
downward to its outer edge, thus taking better advantage of the
flexibility of the larger diameter diaphragm 14 to obtain a longer
stress-free and mechanically uninhibited vertical stroke while incorporating
only one convolution 22 in the diaphragm 14. Also, in order to adjust
the differential pressure of this unit to the desired value, a ring
of material 29 of different density is built into upper diaphragm
plate 24. For example, ring 29 could be a lead insert or the like
molded into a plastic plate 24 e.g. of polyvinyl chloride composition.
Finally, the mast 38 on top of the diaphragm plate assembly in
this device serves as a connecting rod transmitting the vertical
motion of said assembly to the iron core of a linearly variable
differential transformer which is the preferred form of electrical
transducer for my flow meter. Thus, the upper end of mast 38 is
rigidly connected into the lower end of thin-walled sheath tube
50 within which iron core 52 is carried by means of concentric spacer
caps 54 at either end. The upper end of sheath tube 50 is sealed
by means of plug 56 through which adjusting screw 58 entends and
threadably connects into a tapped opening 60 in upper spacer cap
54 in order to simplify final setting of the vertical position of
iron core 52. These parts associated with iron core 52 (such as
50 54 56 and 58) should be constructed of materials of relatively
low magnetic permeability so as not to affect the armature action
of said iron core. Plastic materials such as nylon, polyolefins,
fluoroplastics and the like are ideal for this purpose but various
metals like tantalum and non-magnetic stainless steels can also
be used.
The outer housing 62 of the differential transformer is provided
with a threaded connection 64 for mounting same on top of main housing
10 and a cooperating O-ring element 66 to insure a fluid tight seal
therebetween. Threaded connection 64 has an internal bore somewhat
larger than the outside diameter of sheath tube 50 so as to permit
free vertical movement of same therethrough. The main body of housing
62 encloses bore or cylindrical well 68 which is sized to accept
coil assembly 70 which has an inner core 72 of larger diameter than
sheath tube 50 so that it can be positioned around same with the
electrical leads 71 and 73 passing out the side of housing 62 through
opening 74. After all of the parts of the differential transformer
are in place, the top of housing 62 can be closed by means of seal
cap 76 with the aid of screws 78.
Coil assembly 70 contains a primary winding and at least one secondary
coil. Preferably, two secondary coils of the same configuration
are wound on core 72 equidistantly above and below the center point
thereof or a uniformly wound secondary coil is center-tapped dividing
it electrically into upper and lower sections. In this way when
an alternating current is passed through the primary coil by means
of leads 71 the inductance effect in the secondary will be doubled
due to the push-pull effect of iron core 52. In other words, if
the center of iron core 52 is properly adjusted so as to line up
opposite the center point of coil assembly 70 when the diaphragm
assembly is at its lowest downwardly deflected position (zero fluid
flow), then the induction effect in the opposing secondary coil
sections will be exactly balanced and the electrical output through
leads 73 will be zero. However, as the iron core 52 is lifted from
this null position vertically up through the coil assembly, the
decrease in inductance in the lower secondary section will be of
the same magnitude as the increase in the upper secondary so that
an additive or doubled net electrical signal is emitted through
leads 73 thus insuring a strong, steady and accurate read-out signal
with excellent linearity matching that of the mechanical stroke
produced by the diaphragm assembly as it responds to the fluid flow
rate through the unit. Excellent units of this type can be built
to operate on a very compact overall maximum mechanical stroke,
e.g. a minor fraction of an inch.
One of the prime fields of use for the highly sensitive and linearly
responsive flow meter of this invention if for measuring the flow
of chlorine gas in various chlorination systems, wherein the feed
pressures employed are often below normal atmospheric pressure.
Excellent performance has been experienced in this service provided
the parts which are subject to contact with the chlorine gas are
constructed of suitable materials which include fluorinated polymers,
polyvinyl chloride, acrylonitrilebutadienestyrene copolymers, and
the like or metals such as tantalum or silver.
For example, polymers based upon chlorotrifluoroethylene have excellent
properties. Thus, 5 mil thick sheeting of one such polymer sold
under the registered Trade Mark "Kel-F" has been used
with excellent results to fabricate the flexible annular diaphragms
14 used in the flow meters described hereinabove. In molding the
concentric convolutions in these diaphragms, it has been found desirable
to produce very gently rounded contours and to limit the depth of
groove to no more than about half the main contour radius thereof.
Similar materials including elastomeric fluoropolymers such as
those sold under the registered Trade mark "Viton" can
be used for O-ring elements 36 and 66.
As will be obvious to those skilled in the art, many different
substitutions and modifications can be made in specific elements
of the invention described hereinabove. For example, any suitable
level indicating device, whether mechanical, electrical, magnetic,
electronic etc. can be used to determine the vertical displacement
of the movable element of the limiting fluid flow control passage
of the unit. |