The invention relates to a flow meter and in particular to a flow
meter suitable for connection into a fluid conduit. The flow meter
has an inlet and an outlet for connection into a fluid line and
includes interconnected cylinders, each cylinder having a plurality
of ports controlled by a piston axially-movable therein such that
at any time the inlet and outlet are in fluid communication by a
fluid pathway which includes two cylinders characterized in that
there are three interconnected cylinders.
What is claimed is:
1. A flow meter having an inlet and an outlet for connection into
a fluid line, comprising:
a first, a second and a third cylinder in the meter,
a free piston axially movable within each cylinder, the piston
being movable by fluid flow from the inlet,
each cylinder having a plurality of ports, the ports being controlled
by the free piston,
the meter being adapted so that at any time fluid can flow therethrough
from the inlet to the outlet by a fluid pathway which includes two
of the cylinders,
two fluid passageways for each cylinder, the two fluid passageways
each having one end and another end, wherein the one ends are respectively
connected to two of the ports of each cylinder and the another ends
are respectively connected to two end parts of another of the cylinders,
another port of each cylinder being located between said two of
the inlet being flow connected to said another port of the first
and second cylinders,
the outlet being flow connected to said another port of the third
2. A flow meter according to claim 1 wherein of the three cylinders
the two cylinders providing the fluid pathway between the inlet
and the outlet change in predetermined succession during a flow
meter cycle, wherein the piston in one of said two cylinders is
held stationary whilst the piston in the other of said two cylinders
is movable whereby the piston in the other of said two cylinders
can be driven by inlet fluid at its one end to drive out fluid from
its other end, the piston in the other of said two cylinders being
connected to drive out fluid from a previous part of the cycle towards
the outlet past the piston in said one of the two cylinders.
3. A flow meter according to claim 1 which is adapted to undergo
repeated cycles, wherein during each cycle one of the pistons is
a stationary control piston for another piston, the control piston
being in the fluid pathway connecting the inlet and the outlet,
said another piston being a movable operating piston adapted to
be driven by fluid from the inlet at its one end and to discharge
fluid to the outlet at its other end, the third piston being a stand-by
piston, and during a flow meter cycle each piston is successively
the control piston, the operating piston and the standby piston.
4. A flow meter according to claim 1 wherein the pistons are double
acting, so that the flow meter is self-resetting, for repeated cycling.
5. A flow meter according to claim 1 wherein each piston has a
specific gravity selected to provide neutral buoyancy relative to
the fluid to be metered and wherein each piston has an outer diameter
slightly less than the inner diameter of the cylinder so as to be
movable by the fluid between opposite ends of its cylinder without
6. A flow meter according to claim 1 wherein the cylinders are
housed in a three-part body comprising a central body part and two
end parts, wherein the cylinders are flow connected by passageways
internally of the body, wherein flow passageways are formed in respective
end parts, said end part flow passageways providing a hydraulic
brake for a piston approaching an end part, and wherein the central
body part has an outer wall with flow passageways being formed in
said outer wall, said central body part passageways being annular
7. A flow meter according to claim 1 wherein each of the three
cylinders has axially spaced porting, each cylinder containing an
axially movable piston controlling interconnection between the porting
of its cylinder with that of another cylinder such that the inlet
and outlet can have controlled interconnection by said pistons whereby
to permit flow from the inlet to the outlet but restricting reverse
flow from the outlet to the inlet so that a separate one-way reverse-flow
control valve is not needed.
8. A flow meter according to claim 1 which is adapted to undergo
repeated cycles wherein at any point during a cycle a first cylinder
is an operating cylinder, a second cylinder is a control cylinder,
and a third cylinder is a stand-by cylinder, each of the three cylinders
having axially spaced porting, each cylinder containing an axially
movable piston controlling interconnection between the porting of
its cylinder with that of another cylinder, flow of fluid to the
operating cylinder occurring between the axially spaced ports of
the control cylinder, with a flow path within the control cylinder
being provided by a reduced diameter portion of its piston.
9. A flow meter according to claim 8 wherein the ports are located
in the walls of each cylinder, the ports of each cylinder being
similarly configured, sensing means being provided to check the
presence of one of the pistons at a selected end of its cylinder
and monitoring means being provided to check and respond to the
time interval before said one of the pistons is again at said selected
end of that cylinder, the monitoring means including calculator
means adapted to convert sensor responses into one of the flow rate
or the flow volume of fluid flow through the meter, the sensing
means using pulsed signals, the pulsed signals being powered by
a dedicated battery and the sensing means being attachable to the
flow meter as one of a plug and socket combination.
10. A flow measuring system including a flow meter having an inlet
and an outlet respectively connected into a fluid line and comprising
three cylinders, each cylinder having a plurality of ports controlled
by a free piston axially-movable therein by fluid flow from the
inlet and such that at any time fluid can flow through the meter
from the inlet to the outlet by a fluid pathway which includes two
of the cylinders, two of the ports of each cylinder being flow connected
to respective end parts of another of the cylinders, another port
of each cylinder being located between said two ports, the inlet
being flow connected to said another port of two of the cylinders,
the outlet being flow connected to said another port of the third
11. A flow measuring system according to claim 10 wherein intermediate
flow passageways externally of the cylinders are connected to annularly
spaced branches which break through a respective cylinder wall to
provide the corresponding flow ports, the ports of each cylinder
being axially spaced, the fluid pathway between the ports being
by way of the respective piston internally of the cylinder.
12. A flow measuring system according to claim 10 in a fluid conduit,
the flow meter including pistons movable within respective cylinders,
the cylinders each having an inlet and an outlet port so arranged
with respect to the respective pistons that an inlet port and an
outlet port are in fluid communication during piston stroking so
that flow along the conduit can be continuous, there being three
cylinders, an inlet and an outlet port in a cylinder being arranged
so that they are in fluid 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.
13. A flow measuring system for measuring flow along a conduit
comprising a piston and cylinder arrangement having first and second
and third cylinders and a respective identical piston freely slidable
in each respective cylinder, the arrangement having a main inlet
and a main outlet for being connected in series with the conduit;
each of the first, second and third cylinders having an inlet port
in flow connection with the main inlet, two bi-directional transfer
ports such that the bidirectional transfer ports of one cylinder
section are in flow connection with end ports in the respective
ends of another cylinder, and an outlet port in flow connection
with the main outlet;
the first and second cylinders having an inlet port located between
the transfer ports, the third cylinder having two inlet ports respectively
located between a transfer port and the adjacent end port; each
piston having cylindrical end piston portions, a cylindrical intermediate
piston portion, and a reduced diameter portion connecting the respective
end piston portion to the intermediate piston portion, whereby each
piston of said first and second and third cylinder arrangements
acts, for its respective cylinder as an operator means that (a)
connects the inlet port to one of the transfer ports when the piston
is at one end of the cylinder, and (b) connects the inlet port to
the other transfer port when the piston is at the other end of the
the outlet port of the first and second piston and cylinder arrangements
consisting of two outlet ports being alternately open and closed
with alternating piston end position of a piston of said first and
second piston arrangements;
the transfer ports, the outlet port and the pistons being such
as to move in succession each of the three pistons of the first
and second and third piston and cylinder arrangement when fluid
pressure is supplied to said main inlet; and
means for sensing movement of a piston to measure flow of the fluid;
wherein transfer ports of the first cylinder can by way of the
first piston alternately connect simultaneously an end port at one
end of the third cylinder with the inlet and an end port at the
other end of the third cylinder with the outlet, each of these transfer
ports therefore accepting bi-directional flow, wherein each piston
closes the inlet port or both inlet ports when the piston is at
an intermediate position in the cylinder, at least one of the inlet
ports of said piston and cylinder arrangements being positioned
in the wall of the respective cylinder whereby to be alternatingly
opened on respective sides of the intermediate piston portion when
the piston is at either end position, each of the bidirectional
valve ports in each of the cylinders of said piston and cylinder
arrangements being open on respective opposite sides of the respective
intermediate piston portion at any position of the respective piston.
14. A flow measuring system according to claim 13 wherein the means
for sensing movement of a piston includes a sensor which is in the
piston and cylinder arrangement, the sensor being responsive to
the position of a piston in its cylinder.
15. A flow measuring system according to claim 13 wherein the means
for sensing movement of a piston includes a sensor which is attached
to the piston and cylinder arrangement, the sensor being responsive
to the position of a piston in its cylinder.
16. A flow meter having an inlet and an outlet for connection into
a fluid line, comprising:
a first, a second and a third cylinder in the meter,
a free piston axially movable within each cylinder, the free pistons
being movable by fluid flow from the inlet,
each cylinder having seven ports,
wherein two of the ports are end ports located in end parts of
wherein five of the ports are side ports located in a sidewall
of each cylinder, the side ports comprising an inner side port,
two transfer ports and two outer side ports, the transfer ports
being located between the outer side ports and the inner side port
being located between the transfer ports,
whereby fluid flow through said ports is controlled by the free
the flow meter being adapted so that at any time fluid can flow
therethrough from the inlet to the outlet by a fluid pathway which
includes two of the cylinders,
the transfer ports of each cylinder being connected by respective
fluid passageways to respective end ports of another of the cylinders,
the inlet being connected by a fluid passageway to said inner side
port of the first and second cylinders, the outlet being flow connected
to the inner side port of the third cylinder.
17. A flow meter according to claim 16 wherein each cylinder and
piston is symmetrical, and wherein the inner side port is a central
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 OF 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 meters per hour; to respond
to a minimum flow rate of 0.0075 cubic meters per hour, and above
which accuracy is to be within +/-5%; through a transition flow
rate 0.0115 cubic meters per hour above which the accuracy is to
be within +/-2%, to a maximum flow rate of 2.0 cubic meters 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
The U.K. domestic water pipework is of internal diameter 15 mm
+/-1 mm, so that at minimum and maximum flow rates the mean water
velocities are 0.012 m/s and 3.14 m/s; since the corresponding Reynolds
numbers at ambient conditions are 135 and 36000 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.
Often even the most costly and complicated of current rotary type
water meters fail to meet the above-mentioned Class D standard.
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 movable 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). Treat flow meter is more fully disclosed
for instance in our U.S. Pat. No. 4993262 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.
Advantages of that two-piston 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 leaving
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 downstream 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 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 U.S. Pat. No. 3757581 U.S. Pat. No. 2127773
FR-A-400742 FR-E-11795 and U.S. Pat. No. 2724970 but none of
these disclose the use of free pistons. U.S. Pat. No. 3757582
teaches pistons interconnected by a conrod to a crankshaft. U.S.
Pat. No. 2127773 teaches pistons interconnected by a swash-plate
("wobble plate") device. FR-A-400742 and FR-E-11795
teach the use of only one measuring piston, with the remaining pistons
(merely) being distributors. U.S. Pat. No. 2724970 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 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
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 ire 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 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 between
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 arranged 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).
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 similarly 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 frog the cylinder walls, and preferably float
in the flow medium, being driven by hydraulic rather than mechanical
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.
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
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
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 flaw 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 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
1 mm to 2.25 mm, 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;
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. 1;
FIG. 7 is a section on the line VII-VII of FIG. 1;
FIG. 8 is a schematic developed view of the piston and cylinder
arrangement of the flow meter, with the cylinders connected by "forward"
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;
FIG. 10-15 are schematic views showing successive positions of
the three pistons of the FIG. 1; embodiment during a flow meter
FIG. 16 is a schematic view corresponding to FIG. 10 showing the
start of another flow meter cycle;
FIG. 17 is a schematic sectional view of a sensing device for monitoring
an end position of a piston;
FIG. 18 is a side view of a first alternative piston design; and
FIG. 19 is a side view of a second alternative piston design.
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 15 cm or below (typically 1 cm) and a
length of 25 cm or below (typically 17 cm), 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 1 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 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
2.8 cm; 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 2.0 cm. 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 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 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.
It will be seen from FIG. 5 that cylinders 10 and 20 are open (via
passageways 42a, 42b) to respective outlet channel. 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 to that 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.
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
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. 10-16
and 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 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 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 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 the passageway 42b surrounding
cylinder 20 (FIG. 5), passes to outlet channel 8.
Finally, when in the FIG. 15 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 part 101), and passes to outlet
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 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
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 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
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
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), through 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
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.
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
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
The integrated circuit on board 55 is designed in this embodiment
to effect sensor driving and detecting, as well 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
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 meters. 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 centimeters):
______________________________________ cylinder axial length 14.6
end of cylinder to first ports (122232) 2.8 axial length of first
ports 0.6 end of cylinder to second ports (132333) 4.8 axial length
of second ports 0.6 end of cylinder to centra1 ports (142434)
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 2.8 diameter of piston 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 0.08 cm, and a piston of
effective diameter of 2.8 cm, there 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.
It will be understood from FIGS. 8 and 10-16 that the flow paths
across or past the pistons 100 200 300 is by way of the reduced
diameter portions 101 102 201 202 and 301 302 respectively.
In a first alternative embodiment shown in FIG. 18 the piston 400
does not have reduced diameter portions, but rather has two sets
of apertures 401 and 402 all of apertures 401 being in communication
with each other, and all of apertures 402 being in communication
with each other, by way of respective hollow interior sections of
the piston 400. It is noted for the avoidance of doubt that fluid
cannot flow from any of the apertures 401 to any of the apertures
402. The piston 400 may for example be substantially hollow with
just a central partition preventing fluid flow between the two sets
Whilst the apertures 401 402 are shown to be rectangular, in practice
they can be of any suitable shape, including elliptical or polygonal
for example. It is a particular advantage of elliptical apertures
that the flow is maximised when the center of the apertures are
adjacent the ports, but reduces as the piston moves so that the
ends of the apertures are adjacent the ports. It will be understood
by those skilled in this art that smoothing the edges of the apertures
as much as possible will reduce the pressure drop across the meter.
A second alternative piston 500 is shown in FIG. 19. In this piston,
the sharp edges between the lands and reduced diameter portions
as in the pistons 100 200 300 is replaced by portions of progressively
decreasing diameter 501 502. The provision of such a piston 500
is intended to minimise abrupt changes in the fluid passage areas
which will reduce the multiple serial orifice plate effect.
As a further alternative, the piston 400 could be manufactured
as an open-ended tube with the apertures 401 402 formed therethrough.
A liner of similar form to the piston 500 of FIG. 19 (but with a
correspondingly reduced diameter to be a tight fit within the tube)
could be inserted into the tube to provide the barrier between the
respective sets of apertures and to close off the ends of the tube.
In this alternative, the composite piston would have sets of apertures
beneath which were located the liner portions with progressively
decreasing diameter similar to the portions 502 502 of FIG. 19
and such a piston would also have the advantage of minimising abrupt
changes in passage area. In addition, such a composite piston would
be relatively inexpensive to manufacture.
The length of the "lands" of the pistons 400 500 as
well as the overall length of the piston and its other dimensions,
can be matched to those for the piston 100 200 300 described above
for meet the Class D standard.