Abstrict A liquid flow meter of a rotary positive-displacement kind comprising
a rotor and an idler mounted in a housing having an inlet and an
outlet port. The rotor has blades which are swept around the housing
by the fluid and the idler has pockets within which the rotor blades
are returned from outlet to inlet in a fluid seal. There are four
blades and three pockets, the idler being geared to the rotor so
that the idler rotates four revolutions for every three revolutions
of the rotor. With this arrangement the blades twist very little
while in the pockets and turbulence and drag is consequently reduced,
leading to greater accuracy.
Claims I claim:
1. A liquid flow meter comprising a housing having inner and outer
cylindrical walls defining an annular cylindrical chamber, the outer
cylindrical wall of the housing having therein an inlet port and
an outlet port spaced around the chamber from the inlet port, a
rotor comprising an annular plate portion and a plurality of blades
which depend from the plate portion and which fit the annular chamber
in sealing relationship so that fluid passing along a forward path
from the inlet port of the outlet port around the chamber drives
the rotor by way of the blades, an idler between the outlet port
and the inlet port, and gearing coupling the idler to the rotor
to rotate therewith about an axis parallel with and offset from
the rotor axis, the idler being basically cylindrical and having
longitudinal pockets in its sides, the pockets each accommodating
a rotor blade as the blade returns from the outlet port to the inlet
port and the pocket providing a liquid seal for the rotor blade,
the idler running in sealing relationship with the portion of the
housing wall lying along the return path between the inlet and outlet
ports, the diameter of the idler being greater than half the diameter
of the rotor, the rotor having more blades than the idler has pockets,
the plate portion of the rotor, being provided with upstanding pads
which are machined and are in sliding sealing contact with the cooperating
faces of the idler as the pockets in the idler move along the return
path with a rotor blade accommodated therein, and the gearing rotating
the idler faster than the rotor and the synchronization between
the rotor and the idler being maintained to maintain sealing between
the pads and the cooperating faces of the idler.
2. A liquid flow meter comprising a housing having inner and outer
cylindrical walls defining an annular cylindrical chamber, the outer
cylindrical wall of the housing having therein an inlet port and
an outlet port spaced around the chamber from the inlet port, a
rotor comprising an annular plate portion and a plurality of blades
which depend from the plate portion and which fit the annular chamber
in sealing relationship so that fluid passing along a forward path
from the inlet port to the outlet port around the chamber drives
the rotor by way of the blades, an idler between the outlet port
and the inlet port, and gearing coupling the idler to the rotor
to rotate therewith about an axis parallel with and offset from
the rotor axis, the idler being basically cylindrical and having
longitudinal pockets in its sides, the pockets each accommodating
a rotor blade as the blade returns from the outlet port to the inlet
port and the pocket providing a liquid seal for the rotor blade,
the idler running in sealing relationship with the portion of the
housing wall lying along the return path between the inlet and outlet
ports, the floor of the annular cylindrical chamber being higher
along the portion where it seals with the blades as compared with
the portion where it seals with the idler, and the gearing rotating
the idler faster than the rotor and synchronization between the
rotor and the idler being maintained.
3. A liquid flow meter as claimed in claim 1 wherein the inlet
and outlet ports are in line and wherein right-angle unions are
connected thereto at the ports to direct the flow into and out of
the meter, the inlet portion being provided with a deflecting vane
to reduce turbulence.
4. A liquid flow meter as claimed in claim 3 wherein the deflecting
vane is in two parts, one part being mounted in the input port to
align with the desired incoming flow direction and the other part
being mounted in the rightangle union so that it lines up with the
first mentioned part.
5. A liquid flow meter comprising a housing having inner and outer
cylindrical walls defining an annular cylindrical chamber, the outer
cylindrical wall of the housing having therein an inlet port and
an outlet port spaced around the chamber from the inlet port, a
rotor comprising an annular plate portion and a plurality of blades
which depend from the plate portion which fit the annular chamber
in sealing relationship so that fluid passing along a forward path
from the inlet port to the outlet port around the chamber drives
the rotor by way of the blades, an idler between the outlet port
and the inlet port, and gearing coupling the idler to the rotor
to rotate therewith about an axis parallel with and offset from
the rotor axis, the idler being basically cylindrical and having
longitudinal pockets in its sides, the pockets each accommodating
a rotor blade as the blade returns from the outlet port to the inlet
port and the pocket providing a liquid seal for the rotor blade,
the idler running in sealing relationship with the portion of the
housing wall lying along the return path between the inlet and outlet
ports, an output drive and a calibrator in the output drive, the
calibrator comprising a differential gear having one input, a direct
gear meshed with one input and coupled to said rotor and driven
thereby, and there being provided an infinitely adjustable disc
and wheel gear coupled to and driven by the rotor and in turn coupled
to and driving said differential gear, whereby adjustment of said
disc and wheel gear enables the output of the calibrator to give
an appropriate number of revolutions per unit flow of liquid.
6. A liquid flow meter as claimed in claim 1 wherein the inlet
and outlet ports are in line and wherein right-angle unions are
connected thereto at the ports to direct the flow into and out of
the meter, the inlet port being provided with a deflecting vane
to reduce turbulence.
7. A liquid flow meter as claimed in claim 6 wherein the deflecting
vane is in two parts, one part being mounted in the input port to
align with the desired incoming flow direction and the other part
being mounted in the right-angle union so that it lines up with
the first mentioned part.
8. A liquid flow meter as claimed in claim 5 wherein the wheel
and disc gear acts to reduce the output speed of the calibrator.
9. A liquid flow meter as claimed in claim 5 wherein the diameter
of the idler is greater than half the diameter of the rotor, the
rotor has four blades the idler has three pockets, and the gearing
is such that the idler rotates four revolutions for every three
revolutions of the rotor.
10. A liquid flow meter as claimed in claim 1 the meter having
an indicator drum and a pair of gears on parallel shafts which drive
the indicator drum, one of the gears being coupled to and being
driven by the rotor, the ratio of the gears being such that, by
changing the two gears between the shafts, the indicated output
is changed from gallons to liters and vice versa.
Description The invention relates to a liquid flow meter of a rotary positive-displacement
kind. Such meters have many applications and a principal application
for the present meter is in the measurement of bulk liquid fuel
flow in, for example, the loading and unloading of liquid fuel tankers.
The invention is particularly concerned with a liquid flow meter
of the kind comprising a housing defining an annular cylindrical
chamber having inlet and outlet ports; a rotor comprising an annular
plate portion from which depend a number of blades which fit the
annular chamber in sealing relationship so that fluid passing from
the inlet to outlet around the chamber drives the rotor by way of
the blades; and an idler geared to rotate with the rotor about an
axis parallel with and offset from the rotor axis, the idler being
basically cylindrical with longitudinal pockets formed in its sides,
the pockets each accommodating a rotor blade as the blade returns
from the outlet to the inlet and the pocket giving a liquid seal
for the rotor blade, the idler running in sealing relationship with
a portion of the housing wall. The above defined meter will hereinafter
be called the liquid flow meter of the kind referred to. The present
invention seeks to provide an improved meter of the kind referred
to.
According to one aspect of the present invention the diameter of
the idler is greater than half the diameter of the rotor, the rotor
has four blades, the idler has three pockets and the gearing is
such that the idler rotates four revolutions for every three revolutions
of the rotor.
It has been proposed to use an idler with only two pockets. However,
the use of a larger number of pockets allows a construction in which
the rotor blades twist less relatively to the pockets and thereby
cause less turbulence in the liquid within the pockets. This reduces
drag on the rotor and therefore reduces errors which would be caused
by an increased pressure drop and leaks owing to the drag.
Other features of the invention provide for ease of machining and
assembly of the meter. Thus, according to a preferred aspect of
the invention the plate portion of the rotor is provided with upstanding
pads which are machined to constitute a sliding seal with the co-operating
faces of the idler. By recognising that not all of the surface area
of the plate portion between the blades is used for sealing a difficult
machining operation hitherto thought necessary is avoided, since
it is not necessary to machine the plate portion flat over the whole
region between the blades.
In accordance with another aspect of the invention the floor of
the annular cylindrical chamber is raised over the portion where
it seals with the blades as compared with the portion where it seals
with the idler. This allows the blades of the rotor to be shorter
than the idler so giving a small clearance beneath the blades in
the region where the idler seals with the floor of the chamber.
At this time it is not necessary for the blades to seal with the
floor of the chamber and this arrangement allows a freedom of tolerances
in manufacture compared with an arrangement in which the blades
seal with the floor of the chamber around its whole circumference.
Generally, the inlet and outlet ports of a meter of the kind referred
to are parallel. However, it is sometimes desired to place the meter
in a straight-line conduit, in which case it is possible to insert
right-angle unions at the inlet and outlet ports. However, it is
found that this may give rise to turbulence at the inlet port owing
to incoming fluid tending to cross the inlet port and impinge on
the idler with some force. A feature of the invention which has
been found to reduce the inaccuracies due to such turbulence is
to provide a deflecting vane in the inlet port in such an arrangement.
The deflecting vane may be constructed in two parts, one being mounted
in the port proper to align with the desired incoming flow direction
whether there is a right-angle union or not, and the other part
being mounted in the right-angle union so that when mounted it lines
up with the first-mentioned part.
In order to adjust for the effects of manufacturing tolerances
it is necessary to provide an infinitely variable output gear as
a calibrator in the output drive from the meter. This may comprise
a direct gear which drives one input of a differential gear from
the output of the rotor spindle. In addition, there may be provided
a disc-and-wheel infinitely variable gear which is driven by the
rotor spindle and which, in dependence on its adjustment, adds another
input to the differential gear of an appropriate magnitude to give
a desired number of revolutions per unit fuel flow.
In accordance with another aspect of the present invention such
a calibrator is arranged so that the wheel and disc drive reduces
the overall output speed instead of adding to it. This has the advantage
of allowing a greater torque load to he transmitted by the calibrating
mechanism.
It is commonly desirable to be able to change the output reading
of the meter from gallons to liters. This generally involves changing
a set of output gears between the meter drive and the indicating
drum. Hitherto, it has been necessary to provide a different set
of gears for each required volume measurement. Another aspect of
the present invention provides that the meter drives the indicator
drum through a pair of gears on parallel shafts, the gearing being
such that simply by changing the two gears over on the shafts the
indicated output is changed from gallons to liters or vice versa.
The invention will further be described with reference to the accompanying
drawings, of which:
FIG. 1 is a schematic plan view of a meter in accordance with the
invention;
FIG. 2 is a cross-sectional elevation of the meter of FIG. 1;
FIG. 3 is a perspective view of part of the rotor of the meter
of FIGS. 1 and 2;
FIG. 4 is a view of a meter embodying another aspect of the invention;
FIG. 5 is a cross-sectional elevation of the calibrator of the
meter of FIGS. 1 and 2;
FIG. 6 is a plan view of the output gearing of the meter; and
FIG. 7 is a cross-sectional view taken at G--G of FIG. 6.
Referring to FIG. 1 the meter comprises a cylindrical casing 1
which has an outer wall 2 and a central cylinder 3 between which
is defined an annular chamber 4 coupling an inlet port 5 to an outlet
port 6. A rotor is mounted to rotate about the axis 6a of the housing
and has four blades 7 depending therefrom. The blades fit the chamber
4 in sealing relationship over the upper semi-circular region in
the drawing.
An idler 8 is geared by means of intermeshing gears 9 to rotate
with the rotor. The idler is greater in diameter than half the diameter
of the rotor and has three pockets 10 in its walls. The gearing
9 is such that the idler rotates four revolutions for every three
revolutions of the rotor. The disposition of the pockets 10 is such
that in rotating past a sealing surface 11 with which the idler
seals, a blade 7 is accommodated in each pocket. The blades are
thus returned from the outlet to the inlet of the meter in a liquid
seal. In the drawing, the arrows show the direction of flow of fluid
and of rotation of the idler of the rotor.
Referring now to FIG. 2 the meter is shown in sectional side elevation
and it will be seen that on the right-hand side the blades 7 form
a close sliding seal with the walls and the floor of the chamber
4. The upper part of the chamber is sealed by an annular plate portion
integral with the rotor. This portion is shown at 11a in FIG. 3.
The forward region for the blades is the semi-circular region in
the upper part of FIG. 1 and at the right-hand side of FIG. 2. The
return region is the region adjacent the portion 10. Over the forward
region, the floor of the chamber 4 is raised with respect to the
floor at the return region. This can be seen from FIG. 2 where
there is a clearance 14 between the tip of blade 7 and the floor
of chamber 4. The idler seals against the floor of the chamber at
the return region and it will be seen that the rotor blades are
therefore shorter than the idler in this respect. This means that
extremely close tolerances in machining of the blades in relation
to the idler need not be maintained. The sequence of machining is
important. Firstly, the bore of the housing is machined circular
and the block 15 which fits its base is machined and placed concentrically
to locate within the housing. The second boring operation to house
the idler is then carried out and this again is a completely circular
machining operation. The basic construction allows withdrawal of
the idler from the bottom of the meter and withdrawal of the rotor
from the top, completely independently.
It will be seen that the gears 9 are housed in a dome portion 16
of the rotor. Output gearing 17 is coupled to the rotor shaft to
drive an output shaft 18.
FIG. 3 shows the rotor and in particular it is to be observed that
the bottom face of the annular plate portion 11 is not machined
uniformly but has raised pads 19 between the blades. These pads
are upstanding and seal with the upper face of the idler, it being
unnecessary to machine the plate portion uniformly over the entire
region between the blades 7.
Referring now to FIG. 4 there is shown a meter of the kind shown
in FIGS. 1 and 2 which further has a steel pressure casing 20 surrounding
the housing 1. The housing 1 is formed of cast-iron which is sometimes
not acceptable for high pressure volatile liquids. The outer casing
20 is filled with the pressurised liquid and relieves the pressure
differential from the wall of housing 1.
FIG. 4 shows the configuration of the inlet port where it is desired
to place the meter in line in a straight conduit rather than use
the inlet and outlet ports as parallel ports as shown in FIG. 1.
For straight-line application right-angled unions are applied to
the ports, one of which is shown at 21 in FIG. 4. A difficulty with
this arrangement is that high velocity fluid flowing down the conduit
tends to cross the mouth of the inlet port and impinge with undue
velocity on the idler. This causes turbulence with consequent drag
and loss of accuracy. In order to alleviate this difficulty the
inlet port is provided with a deflector vane. As seen in FIG. 4
the deflector vane is made in two parts, shown at 22 and 23. Part
22 is in the casing of the meter whereas part 23 is in the right-angled
union. The vanes combine to direct the fluid flow in the desired
direction.
Referring now to FIG. 5 there is shown a calibrator mechanism for
fine adjustment of the output of the meter. An input shaft 25 of
the calibrator is coupled to shaft 18 of the meter (FIG. 2). Shaft
25 drives bevel gears 26 and 27 and gear 27 is coupled to drive
an input sun gear 28 of a differential 29. A disc 30 is fixed to
gear 26 and drives a friction wheel 31 which is slideable by screw
adjustment of a screw 32. Wheel 31 drives a gear 33 which is coupled
to the cage gear 34 of the differential 29. Wheel 34 carries the
planet gears 35 and assists in driving the output sun gear 36 of
the differential. This gives the final drive via a bevel gear 37.
The basic drive for the output from the meter is thus given by
shaft 25 through the differential to gear 37. However, an adjustable
increment is subtracted from this drive by means of the friction
wheel 31 and the differential 29. The component subtracted is adjustable
by manipulation of screw 32 so as to give an accurate output. It
is to be noted that the contribution of friction wheel 31 is a decrement
rather than an increment and this has the advantage of allowing
a greater torque load to be transmitted by the calibrating mechanism,
single the torque reaction created by the counter and accessories
being driven by the calibrator tends to assist rather than oppose
the operation of the wheel and disc mechanism.
Referring to FIG. 6 there is shown in plan view the output gear
arrangement for the meter. FIG. 7 is a section taken at G--G of
FIG. 6. Shaft 38 is driven by bevel gear 37 of FIG. 5. Shaft 38
carries two gears 39 and 40. Gear 39 meshes permanently with an
idler gear 41 of the same diameter on a shaft 42. The output shaft
is shown at 43 and carries a gear 44. If forward movement of the
meter with respect to shaft 38 is required then gear 40 meshes directly
with gear 44. The output of the meter and the ratio of the gears
40 and 44 are chosen such that with the larger gear 40 on the input
shaft the output shaft 43 is driven to indicate liters. Furthermore,
the arrangement is such that by simply changing over gears 44 and
40 on shafts 43 and 38 the mesh to drive shaft 43 is in terms of
gallons instead of liters. If reverse motion is required gears 40
and 44 are placed on shafts 42 and 43 instead of shaft 38 and 43.
Again the gears mesh and can be interchanged to give liters of gallons
as required. |