Note: Descriptions are shown in the official language in which they were submitted.
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FLOW METER
FIELD OF THE INVENTION
This invention relates to a flow meter and in particular to
a flow meter suitable for connection into a fluid conduit.
The fluid to be metered may be liquid or gaseous, so that
for instance the flow meter can be connected into a water or
gas conduit to provide a measuring system to meter the
respective flow volume into a dwelling or factory; the meter
can be also fitted into a suitable outflow.
BACKGROUND TO THE INVENTION
Flow meters for public use are required in many countries to
meet specified accuracy standards.
In the United Kingdom the relevant British Standard 5728
(amendment 1-1985) Class D requires domestic water meters to
record from a starting flow rate of 0.00375 cubic metres per
hour; to respond to a minimum flow rate of 0.0075 cubic
metres per hour, and above which accuracy is to be within
+/-5%; through a transition flow rate 0.0115 cubic metres
per hour above which the accuracy is to be within +/-2%, to
a maximum flow rate of 2.0 cubic metres per hour. Turndown
(the ratio between the maximum and minimum flow rates to be
recorded) is thus 267:1.
The specified U.K. pressure drop is to be no more than 0.25
bar at the nominal flow rate, and no more than 1.0 bar at
the maximum flow rate.
The U.K. domestic water pipework is of internal diameter
15mm +/-lmm, so that at miriimum and maximum flow rates the
mean water velocities are 0.012m/s and 3.14m/s; since the
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corresponding Reynolds numbers at ambient conditions are 135
and 36,000 the flow goes from laminar to turbulent over the
flow range.
A water meter suitable for widespread industrial and
domestic fitting could lead to a substantial reduction in
water demand as users become more careful to control waste,
with a reduction in the facilities needed by the water
authorities for processing and storage.
DISCLOSURE OF THE PRIOR ART
Flow meters are in current use, but utilising a so-called
rotary piston. Such flow _meters comprise a cylindrical
measurement chamber with a partition plate separating the
inlet port from the outlet -port. The piston is also
cylindrical, and is guided in the measurement chamber for
oscillatory motion between an inner and an outer boss, by
the engagement of the partition plate with a slot in the
piston.
The rotary flow meter relies on entrapping a fixed quantity
of water (or other fluid) both inside and outside the piston
during each revolution. For accurate metering the resulting
rotational velocity of the piston needs to be proportional
to the rate of fluid flow over the turndown, i.e. including
at the minimum and at the maximum flow rates. Such accurate
metering depends on low internal leakage,-but this has long
proved difficult to achieve because the leak paths
(determined by the rounded geometry) are short in length
though wide in breadth. Also close manufacturing tolerances
are required; and yet mechanical friction should be kept
low, notwithstanding the need for close fits to reduce
leakage, for instance between the outer diameter -of the
piston and the adjacent inner diameter of the measuring
chamber.
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Often even the most costly and complicated of current rotary
type water meters fai.l to meet the above-mentioned Class D
standard. 5 We have previously proposed a flow meter comprising
reciprocable pistons. Though positive displacement, the
pistons are not positively sealed against cylinder internal
leakage and are free to move in response to hydraulic
pressures. The pistons are "double-acting", acting
similarly in both directions of movement along a cylinder
(as a respective control piston for an operating piston).
The control piston connects the inlet and outlet, the said
another piston being a niovable operating piston adapted at
its one end to be driven by.fluid from the inlet and at its
other end to discharge fluid to the outlet i:e. with
positive fluid displacement. This arrangement permits flow
monitoring by the sensing of the axial movement (or
position) of a piston i.e. rather than the sensing of a
rotational piston movement (or position). That flow meter
is more fully disclosed for instance in our USA Patent
4,993,262 the disclosure of which is incorporated herein by
reference. There are two pistons, each double-acting, and
each being successively the control piston and the operating
piston.
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Advantages of that two-pistori flow meter are its high
accuracy, relatively low cost, and dual-direction flow
metering. There are however possible limitations on its
utility mitigating against widespread adoption. Thus the
facility for dual flow direction metering (for monitoring
both forwards or backwards water flow) whilst having the
advantage of perhaps simplifying installation where access
was difficult could in other situations be a disadvantage,
requiring for' instance a one-way valve to be fitted
downstreani e.g. in conduits subject to intermittent high
back pressures, perhaps of contaminated fluid. Furthermore,
because of the use of "free" pistons, at the very lowest
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flow rates internal leakage across the operating piston
central land could perhaps cause the operating piston to
"short-stroke", by causing its control piston to move
prematurely and so cutting off its port controlling flow to
or from the operating piston, with incorrect customer
charging if metering is based on counting the number of
piston strokes, or flow meter cycles; this effect might only
become apparent when the pistons have "worn in" and
frictional resistance to piston movement reduced. Also,
because the control piston is stationary (or nearly so) for
only half the flow meter cycle, at the very highest flow
rates each piston is being worked hard, with considerable
wear and perhaps setting an upper limit to the flow rate
which can be measured without a substantial increase in
meter size.
We are aware of US-A-3,757,581, US-A-2,127,773, FR-A-
400,742, FR-E-11,795 and US-A-2,724,970 but none of these
disclose the use of free pistons. US-A-3,757,582 teaches
pistons interconnected by a conrod to a crankshaft. US-A-
2,127,773 teaches pistons interconnected by a swash-plate
("wobble plate") device. FR-A-400,742 and FR-E-11,795 teach
the use of only one measuring piston, with the remaining
pistons (merely) being distributors. US-A-2,724,970 has
pistons interconnected by an operating (swash) plate, and
has mechanical valve operating means.
We have become aware of a lubricant dispenser using three
reciprocating free pistons; a disclosure occurs in Fig.2 on
Page 181 of "Handbook of Fluid Flow Metering" C.J.Barnard
1988 (Trade and Technical Press, ISBN 85461-120-7). The
flow through each "transfer" port (for transferring flow
from one cylinder to another) is restricted to one way flow,
and thus the port is single function. Another disadvantage
of that arrangement is that the "inlet" and "outlet" ports
for each cylinder are diametrically opposite transfer ports
(leading to or from another cylinder), with (a) a need for
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CA 02187357 1996-10-08
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accurate relative placement to ensure simultaneous
opening/closing so as to avoid a reduction in the available
(cross-sectional) flow area, (b) unequal forces on the
piston, pushing it away from the inlet, increasing wear and
increasing frictional resistance to piston movement and so
setting a lower threshold inlet pressure before the
dispenser will operate, and (c) an increased likelihood of
internal leakage due to the increased hydrodynamic pressure
drop across a port, this pressure drop increasing with flow
rate and piston speed and setting an upper threshold for the
inlet pressure. Thus that meter was designed (only) for
slow moving viscous and lubricating liquids.
DISCLOSURE OF THE INVENTION
We now seek to provide a flow meter overcoming or reducing
these disadvantages, specifically a flowmeter suited to
responding accurately both to low and high flow rates; we
also provide a flow measuring system using the flow meter in
a fluid line, with means responding to piston position so as
to permit calculation of fluid flow through the flowmeter.
For our earlier arrangement we have considered' increasing
the frictional resistance to piston movement, so as to hold
the (stationary) control piston against movement until the
second of the two pistons completes its stroke, and we have
also considered providing a lip seal for the central port;
both of these possible solutions to "central or inlet port
leakage" introduce however further problems.
Alternatively therefore we now propose a flow meter of
special design, with at least three interconnected cylinders
and using free pistons. Thus according to one feature of our
invention we provide a flow meter having an inlet and an
outlet for connection into a fluid line and comprising three
interconnected cylinders, each cylinder having a plurality
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CA 02187357 1996-10-08
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of ports controlled by a free piston axially-movable therein
by fluid flow from the inlet and such that at any time the
inlet and outlet are in fluid communication by a fluid
pathway which includes two of the cylinders, characterised
in that upon piston movement in a cylinder two ports of that
cylinder are alternately connected to the inlet and to the
outlet.
Flow of operating fluid to the operating cylinder occurs
between axially spaced ports of the control cylinder, with a
flow path within the control cylinder being provided by a
reduced diameter portion of the control piston. Similarly
fluid.consequentially.displaced by the operating piston is
discharged to outlet by way of other axially spaced ports of
the control cylinder, with a flow path within the cylinder
being provided by another reduced diameter portion of the
control piston. The axially spaced ports can be annular.
Notwithstanding the provision of a third cylinder there is
provided continuous fluid communication throughout a flow
meter cycle.betweAn the inlet and outlet, and so we provide
a flow measuring system using a flow meter according to the
invention in an hydraulic circuit, the flow meter including
pistons able to stroke in respective hydraulic cylinders,
the cylinders each having hydraulic inlet and outlet port
means so arraqged with respect to the respective pistons
that an inlet port and an outlet port are in hydraulic
communication during piston stroking so that flow along the
conduit can be continuous, there being at least three
cylinders, an inlet and an outlet port in a cylinder being
arranged so that they are in hydraulic communication by way
of the piston in another cylinder, and including means to
determine the number of strokes of a piston in a specified
time (or for sensing movement of a piston to measure flow of
the fluid).
CA 02187357 1996-10-08
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The invention will be further understood by reference to the
appended claims, but the invention also discloses that the
respective two cylinders providing the fluid communication
between inlet and outlet change in predetermined succession
during a flow meter cycle, being for example successively
pistons one and two, pistons two and three, and pistons
three and one. During that part of the flow meter cycle
during which a particular piston pair is active, the first
of said pistons is stationary, or substantially so, whilst
the second is moving, driven by inlet fluid at its one end
and driving out fluid from its other end; such expelled
fluid is from a previous part of the cycle and is driven
towards the outlet past the first piston.
During a flow meter cycle each piston is successively the
stationary control piston for another piston, the moving
operating piston and the standby piston. The volume of
inlet fluid received at one end of the moving piston equates
substantially to the volume expelled by its other end.
Preferably the pistons act simil2rly for each direction of
their axial movement between the ends of their cylinder i.e.
they are double acting; thus the flow meter is self-
resetting, for repeated cycling. The pistons are designed
to move along their cylinder without substantial constraint
i.e. they are freely slidable without significant frictional
resistance fro5 the cylinder walls, and preferably float in
the flow medium, being driven by hydraulic rather than
mechanical pressure.
The cylinders may be housed in a three-part body comprising
a central body part and two end parts. Desirably the
cylinders are flow connected internally of the body, with
flow passageway portions formed in both end parts or
manifolds, and in the outer wall (preferably annular) of the
central body part.
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Usefully the ports in the walls of each cylinder are
similarly configured, but this need not be so. The ports
controlling the phasing of the flow may be either the
cylinder inlet ports or the cylinder outlet ports.
The inlet and outlet can have controlled interconnection by
the pistons and portings being arranged to permit flow from
the inlet to the outlet but restricting reverse flow from
the outlet to the inlet whereby a separate one-way reverse-
flow control valve is not needed.
Desirably the flow meter has sensing means able to check the
presence (or absence) of one of the pistons at a selected
end of its cylinder whereby to determine the flow or flow
rate of fluid between the inlet and outlet i.e. along the
line into which the flow meter is inserted. Preferably the
sensing means uses pulsed signals to minimise power
consumption, provided by a dedicated battery or public
utility. The sensing means may be inbuilt, or attachable to
the flow meter as one of a plug and socket combination.
Thus we further provide a fluw measuring system which
comprises a three piston flow meter, a sensor carried by the
flow meter for detecting the presence of a piston, and
calculator means to convert sensor responses into one of the
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flow rate or the flow volume of fluid flow through the
meter.
Each piston will have cylindrical end piston portions, a
cylindrical intermediate piston portion, and transfer flow
means connecting the end piston portions to the intermediate
piston portion, whereby each piston of said first and second
cylinder arrangements acts, for its respective cylinder
section as a valve operator means. There is a third cylinder
section, also having a respective piston freely slidable
therein; the bi-directional valve ports of the first
cylinder section communicate with ports in the respective
ends of the third cylinder section. The three pistons move
in succession between the said end positions.
The transfer flow means can be respective piston shaft
portions permitting flow therearound.
The provision of a third piston with one piston at current
standby can permit a reduction in the length of the central
lands, and an increase in the length of the central control
port of for instance imm to 2.25mm, yet avoiding the
problems of internal leakage across a respective central
land, whereby to achieve full piston stroking, consistently,
at low flow rates; manufacture can be eased, and internal
pressure drops kept low. Alternatively piston diameter can
be.reduced whilst retaining the ports at the "two-piston"
area.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be further described by way of example
with reference to the accompanying drawings, in which:
Fig.1 is a side elevation of a flow meter according to
the invention;
WU 95/27885 2 18 7 3 5 7 PCT/GB95/00813
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Fig.2 is a view on line II-II of Fig.1;
Fig.3 is a view on the line III-III of Fig.1;
Fig.4 is a central section on the flow meter of Fig.1;
with the inlet and outlet couplings shown in
dotted outline;
Fig.5 is a section on the line V-V of Fig.1;
Fig.6 is a section on the line VI-VI of Fig.l
Fig.7 is a section on the line VII-VII of Fig.l;
Fig.8 is a schematic developed view of the piston and
cylinder arrangement of the flow meter, with the
cylinders connected by "forward" porting;
Fig.9 is a schematic view of the cylinders similar to
that of Fig.8, but with the cylinders connected by
"mixed" porting, as in Figs. 1-7;
Figs.10-15 are schematic views showing successive
positions of the three pistons of the Fig.1
embodiment during a flow meter cycle;
Fig.16 is a schematic view corresponding to Fig.10,
showing the start of another flow meter cycle;
and,
Fig.17 is a schematic sectional view of a sensing device
for monitoring an end position of a piston.
WO 95127885 218 7 3 5 7 PCTIGB95/00813
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DESCRIPTION OF EXEMPLARY EMBODIMENTS
The flow meter 1 is designed to respond to water flow along
a conduit (not shown). There is a provision (in the
embodiment of Fig.1 by end socket 50) for the fitment of a
recording device 51 (Fig.17) for logging the flow meter
response, to permit monitoring of the volume of water which
passes through the flow meter and thus along the conduit;
with the recording device fitted, the flow meter can be used
for instance to check the volume of water used by a customer
(perhaps for customer billing) or the volume of water used
in an industrial process (perhaps for quality control), with
the logging being local to the flow meter or transmitted to
a distant location.
For domestic applications and anticipated flow rates the
flow meter 1 will have a diameter of 15cm or below
(typically ilcm) and a length of 25cm or below (typically
17cm), the lowest size achievable being in part determined
however by internal pressure drops (which increase inversely
as the fourth power of diameter).
The flow meter l can be connected into the specified conduit
using inlet coupling 2 and outlet coupling 3. Usefully the
inlet and outlet couplings are threaded at both ends, and
can either be separate components or as seen in Fig.4 can be
combined into a unitary member, in both cases as an end
connection to concentric inlet and outlet channels (Fig.4).
In an alternative embodiment the couplings can be a side
connection mid-way along the length of the flow meter, and
in another alternative embodiment the inlet coupling can be
at one end of the meter and the outlet coupling at the other
end.
As more clearly seen in Fig.4 the flow meter 1 has a central
body part 4, and end body parts 5,6. The end body parts can
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WO 95127885 2187357 PCT/GB95/00813
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be welded to the central body part, or can be otherwise
sealingly coupled thereto as by tie bars.
The central body part 4 has three axially extending
cylinders 10,20,30 (Figs. 5-7), equilaterally spaced about
the longitudinal axis of the central body part 4, and in
this embodiment of bore 2.8cm; at opposite cylinder ends are
piston end stops 9 (Fig.2), determining for each piston its
full stroke length. In an alternative embodiment the
cylinders can include a sealed liner of a different material
to that of the body part 4. Each cylinder is adapted to
receive a respective piston 100,200,300 (Fig.8), each piston
being of the same outer diameter and each with two parts of
reduced section i.e. 101,102; 201,202; and 301,302; for a
purpose to be described below. In this embodiment each
piston has a stroke of 2.0cm. The meter materials of this
embodiment are selected to accommodate river and underground
derived waters in the pH range 6.9 to 8.5, preferably an
even wider pH range, whilst continuing to meet the Class D
standard.
There are seven internal passageways for each respective
cylinder, formed usefully by a lost wax or lost metal
process; these passageways are axially-spaced along the
length of each cylinder. These comprise two end passageways
41 and 47 formed in conjunction with respective end body
parts 5,6; and five intermediate passageways 42,43,44,45 and
46.
Each intermediate passageway has associated therewith a
number of inwardly directed branches which break through the
cylinder wall to provide corresponding flow ports. Thus,
cylinder 30 has end flow ports 31 and 37, and side flow
ports 32,33,34,35 and 36; the ports 32 are connected to
passageway 42, the ports 33 are connected to passageway 43
and so on. Similarly, and as indicated schematically in
Fig.9, cylinder 10 has end flow ports 11 and 17, and side
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flow ports 12,13,14,15 and 16; cylinder 20 has end flow
ports 21 and 27, and side flow ports 22,23,24,25 and 26.
In this embodiment corresponding ports are of identical
shape and cross-section, and disposition along the
respective cylinder, but though preferable this need not be
so.
The size of the passageways, and the size and disposition of
the branches and ports, will preferably be chosen to
minimise hydraulic pressure drop. As more particularly seen
in Fig.4, the passageways 43,44 and 45 are of larger cross-
section adjacent the central axis of the flow meter i.e.
where there is a larger volume of water flow to be
accommodated than at the outer periphery when much of the
water has already left the passageway and entered into the
cylinder (through a branch and port).
The arrangement for the water flow to enter a cylinder from
an intermediate passageway 43,44 or 45 through a number of
circumferentially spaced side flow ports (i.e. spaced around
the cylinder longitudinal axis) as seen in Fig.4 through
grouped side flow ports, helps to provide a balanced water
flow, not only into but just as importantly out of the
25- respective cylinder; it furthermore encourages the
respective piston to "float" centrally in the cylinder
(rather than being biassed by a single water inflow jet
against the cylinder opposed wall portion) and so helps
reduce sliding friction during axial traverse of a piston
along its cylinder.
The sectional views of Fig.5, Fig.6 and Fig.7 show the
intermediate porting at the specified position along the
cylinders. For simplicity in these figures, the passageways
42,43 and 44, the outlet channels 8 and the transfer
channels 9 are given the suffix a,b or c, according to
whether they relate to cylinder 10,20 or 30 respectively.
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It will be seen from Fig.5 that cylinders 10 and 20 are open
(via passageways 42a,42b) to respective outlet channels
8a,8b, which communicate with outlet coupling 3, whilst
cylinder 30 is open (via passageway 42c) to the (generally
triangular) central inlet channel 7, which communicates with
inlet coupling 2.
It will be seen from Fig.6 that all three cylinders 10,20,30
are open (via passageways 43a,43b,43c) to the (generally
pear shaped) transfer channels 9a,b,c respectively.
It will be seen from Fig. 7 that cylinders 10 and 20 are
open (via passageways 44a,44b) to the inlet channel 7 whilst
cylinder 30 is open (via passageway 44c) to the outlet
channels 8c.
To assist the floating action each piston is fabricated so
as to have a specific gravity similar tothat of water, or
if the flow of another liquid is being monitored to have the
specific-gravity of that liquid, and thus preferably has
neutral buoyancy. Suitably the pistons may be hollow, and
in one embodiment comprise two half-shells welded together
along an axially extending plane at the outer periphery and
also at internal strengthening walls or partitions.
To. help reduce impact wear and noise for liquid flow
measuring applications, each cylinder end part can be
designed to provide an hydraulic brake (but not an hydraulic
stop). In particular the size and shape of the passageways
41,47 formed in one or both of the end body parts 5,6 can be
selected so as to cooperate with an approaching piston to
provide a pre-determined resistance requiring forced
hydraulic outflow for continued piston movement, until
further movement is prevented by a piston end stop 9.
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In a preferred embodiment a progressively greater resistance
to hydraulic flow can be used, such that a piston
approaching at or near its maximum speed (maximum flow rate)
meets the highest resistance and is also therefore brought
to rest or nearly so before abutting the end body part.
Thus damage to the piston and/or end body part, and impact
noise during operation of the meter, are reduced.
In the developed schematic porting arrangement of Fig. 8 the
inlet channel 7 is connected to ports 14,24, and 34. For
clarity only a single respective port is shown, though
preferably the inlet will connect to multiple
(circumferentially spaced) ports by way of passageways 44
and respective inwardly directed branches, as described
above with reference to Fig.4.
The outlet 8 is connected to ports 12,16; 22,26; and 32,36,
again for clarity shown as a respective single port;
preferably however the outlet will again connect to multiple
(circumferentially spaced) ports by way of passageways 42,46
and respective inwardly directed branches.
It will be observed that in the Fig.8 ("forward" porting)
embodiment the transfer channel connecting ports 31 and 15
needs to cross the transfer channel connecting ports 37 and
13. It has been found that this can add to the
manufacturing complication if desire ably these lines are
internal of the flow meter body; thus the functioning of the
flow meter of the invention will be described in relation to
an alternative ("mixed") porting embodiment with particular
reference to the subsequent showings of Figs 10-16and which
relate to the Figs.1-7 and Fig.9 arrangement.
Other than this possible manufacturing complication arising
with the Fig.8 line connections, not present of course if
external lines are used (since the problem of providing
transfer lines which cross internally of the meter body is
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not present, or alternatively that the problem of providing
such crossing without a significantly increased pressure
drop is not present), the two meter designs are equivalent
in improved performance and suitability for domestic and
commercial applications. In particular the cylinders and
pistons are identical for the two embodiments, differing
only in the interconnections between some of the ports.
Referring therefore to Fig. 9, inlet channel 7 is connected
to port 14 of cylinder 10, to port 24 of cylinder 20, and to
ports 32 and 36 of cylinder 30. outlet channel 8 is
connected to ports 12 and 16 of cylinder 10, to ports 22 and
26 of cylinder 20, and to port 34 of cylinder 30.
In addition transfer lines 18 respectively connect the ports
11,23; 21,33; 31,13; as well as 17,25; 27,35; 37,15.
Whilst for drawing simplicity, port 34 is shown connected to
outlet 8 only via cylinders 20 and 10, it will be understood
that whilst the port is connected to those cylinders by way
of transfer lines, it is also directly connected to outlet
channel 8 (see Fig.7), i.e. the positions of the pistons 100
and 200 do not affect the ability of fluid to flow from port
34 to outlet channel 8. Likewise, inlet channel 7 connects
directly to port 14 and 24 (see Fig.7); the position of
piston 100 does not affect the ability of fluid to flow from
inlet channel 7 into port 24.
Whilst any start position can be selected, the presumed
start position is with each piston at the left hand end of
its cylinder, as viewed in Fig.10 (and in Fig.16).
In describing the operation of the meter as shown in
Figs.10-16, for clarity only those channels through which
flow can take place are drawn; it will be understood, with
reference to Fig.9, that there is no flow through the
channels which are not drawn, though the pressure of water
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in those channels may act to prevent movement of the
stationary pistons.
in operation, inlet flow through port 32 (having first
passed along and/or around the reduced section part 301 of
piston 300) will outflow through port 33 and enter the left
hand end of cylinder 20 i.e. through port 21, whereby to
move piston 200 to the right i.e.- to the position shown in
Fig.11.
The fluid displaced from the right hand end of cylinder 20
exits through port 27 and enters cylinder 30 through port
35. This fluid exits cylinder 30 through port 34, and via
the passageway 44c (see Fig.7), passes to outlet channel 8.
When piston 200 reaches the right hand end of cylinder 20
its movement is arrested notwithstanding that the inlet
pressure is still being applied through port 21. However
this movement of piston 200 has connected ports 23 and 24,
allowing inlet flow from port 24 (via passageway 44b (Fig.7)
and along and/or around reduced section piston part 201) to
flow to the left-hand end of cylinder 10 where it passes
through port 11 to move piston 100 to the right, until the
pistons have the positions shown in Fig.12.
The fluid displaced from the right hand end of cylinder 10
exits through port 17 and enters cylinder 20 through port
25. This fluid exits cylinder 20 through port 26, and via
the passageway 46b (similar to passageway 42b of Fig.5),
passes to outlet channel 8.
In moving to the Fig.12 position, the piston 100 has
connected ports 13,14 allowing the inlet flow from port 14
to transfer to the left hand end of cylinder 30 (having
first passed along and/or around the piston reduced section
part 101), where it passes through port 31 to move the
WO 95/27885 ~ 1 C3C$7357 PCT/GB95/00813
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piston 300 to the right i.e. until the pistons have the
position shown in Fig.13.
The fluid displaced from the right hand end of cylinder 30
exits through port 37 and enters cylinder 10 through port
15. This fluid exits cylinder 10 through port 16 and, via
passageway 46a (similar to passageway 42a of Fig.5), passes
to outlet channel 8.
In the condition of Fig.13, each piston 100,200,300 is to
the right hand end of its respective cylinder as viewed i.e.
the end opposite to that of Fig.10 at presumed cycle start.
With piston 300 in the Fig.13 position, the outlet port 34
is uncovered and so the inlet flow can pass by way of port
36 and port 35 (having first passed around and/or along
piston reduced section part 302) to the right hand end of
cylinder 20, and passes through port 27 to move the piston
200 back to the left, i.e. until the pistons have the
position shown in Fig 14.
The fluid displaced from the left hand end of cylinder 20
exits through port 21 and enters cylinder 30 through port
33. This fluid exits cylinder 30 through port 34, and via
the passageways 44c (Fig.7), passes to outlet channel 8.
In.its left-hand position of Fig.14, piston 200 permits
inlet flow from port 24 to pass through port 25 (having
first passed along and/or around piston reduced section part
202) and hence to the right hand end of cylinder 10 through
port 17, whereby to move piston 100 to the left hand end of
its cylinder 10 i.e. to the position seen in Fig.15.
The fluid displaced from the left hand end of cylinder 10
exits through port 11 and enters cylinder 20 through port
23. This fluid exits cylinder 20 through port 22, and via
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the passageway 42b surrounding cylinder 20 (Fig.5), passes
to outlet channel 8.
Finally, when in the Fig.l5 position, the piston 100 permits
flow from inlet port 14 to pass to transfer port 15 (having
first passed along and/or around piston reduced section part
102) and thus to end port 37 of cylinder 30, to move piston
300 to the left i.e. until it reaches the left hand end of
the cylinder 30.
The fluid displaced from the left hand end of cylinder 30
exits through port 31 and enters cylinder 10 through port
13. This fluid exits cylinder 10 through port 12 (having
first passed along and/or around the piston reduced section
15-part 101), and passes to outlet channel 8.
Thus, the positions of all three pistons are now as seen in
Fig.16, and this is the same as for Fig.10 i.e. the cycle is
ready to be repeated.
It will be understood that at different piston positions
during a cycle, one of the pistons permits water inlet flow
to and outlet-flow from one or other end of a "neighbour"
cylinder. For piston 100 the water flows to or from one or
other end of cylinder 30; for piston 200, the water flows to
or from one or other end of cylinder 10; for piston 300, the
water flows to or from one or other end of cylinder 20.
Each piston in turn, whilst stationary or substantially so,
controls -flow into and out of another cylinder, with
operational movement of the (second) piston in that cylinder
from one end to the other; and whilst this is occurring the
third piston is at standby, stationary or substantially so.
It will also be understood that, as above described,
movement of a piston along a cylinder consequent upon inlet
flow causes the expulsion of the fluid in front of that
A'U 95/27885 2 1 O 7 3 5 7 PCT/GB95/00813
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piston. The fluid expelled- retraces the first part of its
path, travelling back along the respective transfer channel
but when it reaches the intermediate transfer port, the
movement-of the other piston(s) which has occurred in the
meantime means that the transfer channel is now in fluid
communication with the outlet-channel 8.
This flow and ebb of the inlet water, to and from the end
spaces of the neighbouring cylinder under the control of a
piston as it moves, is repeated in'succession during a flow
meter cycle, with continuous water flow from inlet channel 7
to outlet channel 8, notwithstanding that the pistons have
successive stationary or dwell periods.
The flow meter thus comprises reciprocable pistons, in which
one of the pistons is a stationary control piston for
another piston, the control piston connecting the inlet and
outlet; and in which the said another piston is a movable
operating piston adapted to be driven by fluid from the
inlet at its one end and to expel fluid to the outlet at its
other end. There is also a third piston at standby or
waiting to participate; during a flow meter cycle each
piston is successively the control piston, the operating
piston and the standby piston.
Each piston is dual function, as a positive displacer for
metering, and (earlier and later) as a valve member to
control flow to and from an adjacent piston, respectively
moving and stationary, with also, as above, a stationary
non-operating stand-by mode.
One major advantage of the disclosed three-cylinder
arrangement is the avoidance of operating piston short-
stroking. Clearly for a full operating piston stroke,
piston 200 (the current operating piston) must travel from
its (left hand) position as shown in Fig.10 to its (right
hand) position of Fig.11. Piston 200 is so moved because of
WO 95/27885 - 19 - 2187357 PCT/GB95/00813
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inlet flow to its port 21 from port 33 of the current
control piston 300.
This-required full stroking of the current operating piston
e.g. 200, is possible notwithstanding probable premature
flow between ports 24,23 due to leakage across the piston
200 central land as it moves rightwards (as viewed), because
this premature leakage flow is directed to piston 100
(currently at "standby"). Specifically, as compared to our
earlier "two-piston" arrangement this "premature" flow is
not directed to the current control piston, since if it were
it could move that control piston (to the right) to curtail
(prematurely) the "further" inlet flow needed to move the
operating piston through its full traverse to the right.
- -
Alternatively stated the piston caused to move prematurely
by the leakage across the operating piston land is no longer
the piston controlling the flow to the operating piston.
Another major advantage of the three cylinder arrangement is
that the cylinder porting and the contained pistons control
the flow of fluid from the inlet 2 to the outlet 3 in such
manner that reverse flow is substantially prevented i.e. the
unit is a combination flow meter and one-way flow valve.
This is so whether the reverse flow (assumed to be from
outlet channel 8) seeks to move pistons simultaneously, or
as. is more likely with manufacturing tolerances and
differential flow resistances to cause one to move with
priority i.e. before the others.
Thus assuming the pistons are in position as seen in Fig.10
the reverse flow through cylinder 10 moves (priority) piston
300 to the right. Flow though ports 34,33 then moves piston
200 to the right. Flow through ports 26,25 then acts to
hold piston 100 at its left hand cylinder end, to lock the
pistons against further movement.
WO 95/27885 2 1 8 7 J5f PCT/GB95/00813
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If the fluid lines are assumed to be of equal flow
resistance, without priority piston movement, then
alternatively considered in relation to the arrangement of
Fig.8, reverse flow from outlet 3 seeks to enter the flow
meter through channel 8, and in the piston positions shown
seeks to move pistons 100 and 200 to the right. Piston 100
is permitted only a limited rightwards movement, being
arrested as soon as port 24 is closed (since the fluid to
the right of the piston 100 is trapped), though piston 100
may have moved sufficiently to block off port 12 from
channel 8. Piston 200 can move to its right hand end
position.
in its right hand position piston 200 allows a limited flow,
which acts to force piston 100 back to the left; with in
turn piston 300 being held to the left, and piston 200 being
held to the right.
In the arrangement of Fig.9, starting with each piston at
the left hand end of its cylinder, reverse flow from channel
8 holds piston 200 in position; and seeks to move pistons
100 and 300 to the right hand end of their cylinders.
Piston 300 however is arrested when port 12 closes, piston
100 moving to the right hand end of its cylinder.
-
Piston 300 is now forced back to onto its left hand seat, by
flow through ports 16 and 15; piston 100 continues to have
pressure at its left hand end, and so remains in position.
The number of cycles performed by the pistons can be counted
by checking the position or movement of only one piston, at
one cylinder location. One suitable sensing means is an
infra-red emitter and detector device 51 (Fig. 17), which in
this embodiment is made as a plug to fit into the socket 50,
but which in an alternative embodiment includes acrylic
inserts in the central body part 4.
WO 95/27885 2187357 PCT/GB95/00813
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The device 51 has an emitter 52 with an adjacent detector
53, both being carried in block 54, transparent or
significantly so to wavelengths in the infra-red region.
Printed circuit board 55 is secured to block 54 and is
protected by cover 56. The infra-red beam will be
interrupted by the piston projection 57; in an alternative
embodiment the emitter and detector are adjacent so that the
detector responds to reflected infra-red light (or in the
reversed circuitry to its absence).
In a preferred embodiment the infra red beam is pulsed, to
reduce power consumption. The duration of dwell of a piston
at one end of its cylinder can be calculated for the highest
flow rates, and the pulsed rate selected such that the
circuitry can readily distinguish between the signal gaps
arising from the mark-space pulse pattern and the signal
gaps from the interrupting presence of piston projection 57;
a suitable ratio for measured pulse gap to distinguish
between interruptions in the received signal arising e.g.
from piston projection 57, and from the set mark-space
ratio, is 10:1.
In an alternative embodiment a piston carries an annular
insert inset into its outer periphery and the presence (and
absence) of which can be detected by a sensor in or attached
to the wall of the central body part 4. This embodiment
could have the advantage of a small detection gap. The
sensor could be a pyroelectric detector with the piston
(preferably without probe) proving the emitter, in that the
detector operates in response to temperature changes arising
from the alternating presence or absence of water. In
further alternative embodiments the presence or absence of
the piston can be sensed magnetically (usefully with a Hall
effect sensor), or inductively.
The integrated circuit on board 55 is designed in this
embodiment to effect sensor driving and detecting, as well
WO 95/27885 2 18 7357 PCT/GB95/00813 =
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as counting, number storage (i.e. completed cycles since
last inspection or since initial fitting), and (local)
number display; and also drives an output to a remote
indicator. Usefully it. includes a dedicated lithium
battery, for long shelf life and substantially maintenance
free service.
In one embodiment each logging pulse is generated by a
transistor buffer output stage which is capable if necessary
of transmitting the pulse a distance of 0.5 metres. The
width of a pulse is conveniently 50 milliseconds. In an
alternative arrangement the output signal may utilise more
than one pulse for each unit of flow i.e. for each flow
meter cycle. -
One embodiment of flow meter to meet the aforesaid Class D
(British Standard 5728) has the following dimensions (all in
centimetres):-
cylinder axial length 14.6
end of cylinder to first ports (12,22,32) - 2.8
axial length of first ports 0.6
end of cylinder to second ports (13,23,33) 4.8
axial length of second ports 0.6
end of cylinder to central ports (14,24,34) 7.1
axial length of central ports 0.4
piston axial length 12.6
axial length of end land 2.8
axial length of central land 1.8
axial length of reduced section piston part 2.6
both piston and cylinder axially symmetrical
diameter of piston 2.8
diametral clearance (piston to cylinder) 0.0075
Because the pistons are free floating, with a diametral
clearance which with a suitable length overlap (between the
piston, and the cylinder wall between any two ports) of
0.08cm, and a piston of effective diameter of 2.8cm, there
WO 95/27885 - 23 - 21 8) 357 PCT/GB95/00813
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is an acceptable rate of leakage, even with acircular
pistons and cylinders; any piston tendency to short stroke
(with two-cylinder meters now recognised as a likely
consequence of this leakage) is tackled by the provision of
the third cylinder as explained above. Furthermore, instead
of a piston with an intermediate and two end lands as
indicated in the Figures, a piston of uniform cross-section
but having three hollow chambers, each with porting for
valve control and fluid transfer, can be used.
