Abstrict In a flow meter, a cylindrical member containing therein a vane
wheel is fitted in a measuring chamber of a casing so as to be closely
in contact with the peripheral wall of the casing, and a cover is
put on the cylindrical member. Rectangular inlet and outlet nozzles
in a side wall portion of the cylindrical member communicate with
inlet and outlet ports of the casing, respectively. A pivot supporting
the vane wheel is replaceably attached to a bottom portion of the
cylindrical member. A supporting shaft of the vane wheel extends
upward through a center opening in the cover to be connected to
a measuring mechanism.
Claims What we claim is:
1. A flow meter with a casing having an inlet port, an outlet port,
and a measuring chamber containing therein a vane wheel, comprising:
an integral bottomed cylindrical member of synthetic resin including
a bottom portion and a side wall portion which is fitted in said
measuring chamber so as to be closely in contact with the peripheral
wall of said measuring chamber and has an inlet nozzle and an outlet
nozzle corresponding to said inlet and outlet ports, respectively;
a cover of synthetic resin put on said cylindrical member;
a pivot rotatably supporting said vane wheel, said pivot being
set in the center of the bottom portion of said bottomed cylindrical
member;
a supporting shaft of said vane wheel connected to a measuring
mechanism over said measuring chamber through an opening in the
center of said cover; and
penetrating holes for instrumental error adjustment formed in the
side wall portion of said bottomed cylindrical member in the vicinity
of said inlet and outlet nozzles so as to correspond to the inlet
and outlet ports of said casing, respectively, the cross-sectional
flow area of each said penetrating hole being restricted to a proper
value by manually adjustable restricting means.
2. The flow meter according to claim 1 wherein a plurality of
ribs radially extending from said pivot are formed integrally on
the inner surface of the bottom portion of said bottomed cylindrical
member, and a plurality of ribs arranged around said opening are
formed integrally on the inner surface of said cover.
3. The flow meter according to claim 1 wherein said restricting
means is formed of screws screwed into the side wall portion of
said bottomed cylindrical member so that one end of each said screw
can project into each corresponding one of said penetrating holes.
4. The flow meter according to claim 1 wherein said inlet and
outlet nozzles are rectangular, and the upper end of each said nozzle
is opened at a top edge of the side wall portion of said bottomed
cylindrical member.
5. The flow meter according to claim 1 wherein said bottomed cylindrical
member is positioned by fitting a projection formed integrally on
the outer surface of the bottom portion of said bottomed cylindrical
member in an indentation formed in said casing so as to correspond
to said projection.
6. A flow meter with a casing having an inlet port, an outlet port,
and a measuring chamber containing therein a vane wheel, comprising:
an integral bottomed cylindrical member of synthetic resin including
a bottom portion and a side wall portion which is fitted in said
measuring chamber so as to be closely in contact with the peripheral
wall of said measuring chamber and has an inlet nozzle and an outlet
nozzle corresponding to said inlet and outlet ports, respectively;
a cover of synthetic resin put on said cylindrical member;
a pivot rotatably supporting said vane wheel, said pivot being
set in the center of the bottom portion of said bottomed cylindrical
member;
a supporting shaft of said vane wheel connected to a measuring
mechanism over said measuring chamber through an opening in the
center of said cover;
a circumferential groove formed in the outer peripheral surface
of the side wall portion of said bottomed cylindrical member so
that one and the other ends of said groove communicate with said
inlet and outlet ports, respectively; and
manually adjustable restricting means for restricting the cross-sectional
flow area of said groove to a proper value.
7. The flow meter according to claim 6 wherein said restricting
means is formed of a screw screwed into said casing so that one
end of said screw can project into said groove.
8. A flow meter with a casing having an inlet port, an outlet port,
and a measuring chamber containing therein a vane wheel, comprising:
an integral bottomed cylindrical member of synthetic resin including
a bottom portion and a side wall portion which is fitted in said
measuring chamber so as to be closely in contact with the peripheral
wall of said measuring chamber and has an inlet nozzle and an outlet
nozzle corresponding to said inlet and outlet ports, respectively;
and
a pivot rotatably supporting said vane wheel, said pivot including
a tip bearing portion, a shank portion, and a support portion fitted
in the center of the bottom portion of said bottomed cylindrical
member so as to be supported thereby, said support portion having
an extended head, and said pivot being inserted from the outside
of the bottom portion of said bottomed cylindrical member into a
shaft hole penetrating the center of said bottom portion so that
said head is fitted in a spot facing groove around said shaft hole.
9. The flow meter according to claim 8 wherein said head and said
spot facing groove corresponding thereto are rectangular.
Description BACKGROUND OF THE INVENTION
This invention relates to a flow meter for measuring the rate or
quantity of flow of tap water as a fluid flowing through a casing.
Flow meters of this type have a casing which is provided with inlet
and outlet ports and a measuring chamber containing therein a vane
wheel. A fluid introduced into the measuring chamber through the
inlet port rotates the vane wheel, and the number of rotations is
measured by a measuring mechanism disposed over the measuring chamber.
Then, an indicator section including a counter visually indicates
the measured quantity of flow or consumption. In this case, nozzles
with a fixed cross-sectional flow area are generally formed aslant
in the wall of the measuring chamber so as to correspond to the
inlet and outlet ports, in order to cause the fluid positively to
act on the vane wheel, thereby minimizing the instrumental error
or the discrepancy between the flow quantity and its corresponding
measured number of rotations of the vane wheel.
In a prior art flow meter 1 shown in FIGS. 1 to 3 an inlet nozzle
6 and an outlet nozzle 7 open into a measuring chamber 5 so as to
correspond to an inlet port 3 and an outlet port 4 of a casing 2
of the meter 1. The inlet and outlet nozzles 6 and 7 extend aslant
along axes X--X and Y--Y (FIG. 3), respectively, and tangential
to the rotating direction of a vane wheel 8. A fluid or tap water
to be measured is led into a measuring chamber 5 through the inlet
nozzle 6 to rotate the vane wheel 8. The rotation of the vane wheel
8 is transmitted through its supporting shaft 9 to a measuring mechanism
10 formed of a number of gears. The measurement result is visually
indicated by an indicator section 12 (FIG. 1) including a counter
11.
In the conventional meter of this type, instrumental errors are
adjusted by a pair of adjusting plates 13 and 14 having the vane
wheel 8 in the measuring chamber 5. The adjusting plates 13 and
14 are intended to adjust the so-called forward flow. In adjustment,
the adjusting plates 13 and 14 are moved symmetrically. Each of
the adjusting plates 13 and 14 can rock around its shaft 16 and
can also be fixed to a fixed supporting plate 15 in a suitable angular
position by retaining means 17 formed of a setscrew and a slot.
Thus, the action of the fluid on the vane wheel 8 may be controlled
by changing the angular positions of the adjusting plates 13 and
14 to adjust the resistance against the incoming fluid.
The vane wheel 8 is rotatably supported by a pivot 18 fixed to
the casing 2. The pivot 18 is fixed upright in the center of the
measuring chamber 5 by means of a supporting member 20 screwed in
a tapped hole 19 in the bottom of the measuring chamber 8 and a
nut 21 fitted on the lower end portion of the pivot 18.
The casing of the meter of this type is generally formed by casting
a metal such as bronze, and the nozzles are formed by machining
afterwards. However, the nozzles must be accurately worked in a
slanting manner, as shown in FIG. 3 requiring hard and complicated
machine work.
With use of the adjusting plates of the prior art meter, instrumental
error adjustment for the forward flow side may exert an influence
on adjustment for the counter flow side, and it is difficult to
make proper, well-balanced adjustment for both flow directions.
This is an inevitable situation so long as the flow resistance is
controlled for adjustment. Usually, therefore, a method is adopted
in which the instrumental errors on the forward flow side are minimized
at the sacrifice, in some measure, of the adjustment for the counter
flow side.
The use of the adjusting plates widens the inside space of the
measuring chamber, constituting a hindrance to the miniaturization
of the meter as a whole.
Moreover, the manner of pivot fitting requires a tapped hole in
the casing and troublesome assembly work for fitting the pivot in
the tapped hole. Since the fitting portion of the pivot is complicated
in structure, replacement of the pivot once set in place requires
troublesome work, such as removal of the supporting member from
the tapped hole. Thus, the construction and operation of the meter
need be simplified or facilitated.
SUMMARY OF THE INVENTION
Accordingly, the object of this invention is to provide a flow
meter of a compact design, enjoying facilitated parts assembly,
improved measuring performance, and easy pivot replacement, without
requiring the troublesome, high-accuracy machine work as is required
by the casing of the prior art meter.
In order to attain the above object, a flow meter according to
this invention is so constructed that an integral bottomed cylindrical
member of synthetic resin including a side wall portion and a bottom
portion is fitted in a measuring chamber so as to be closely in
contact with the peripheral wall of the measuring chamber. Inlet
and outlet nozzles are formed in the side wall portion of the cylindrical
member so as to take the form of penetrating holes corresponding
to inlet and outlet ports, respectively, when the bottomed cylindrical
member is fitted in the measuring chamber. A cover of synthetic
resin is put on the bottomed cylindrical member, and a pivot rotatably
supporting a vane wheel is provided in the center of the bottom
portion of the cylindrical member. A supporting shaft of the vane
wheel extends upward through an opening in the center of the cover
to be connected to a measuring mechanism located above the cover.
Thus, the nozzles and the fitting portions of the pivot are all
formed in the bottomed cylindrical member, so that the casing does
not require any accurate machine work. Moreover, the bottomed cylindrical
member can readily be formed from synthetic resin. Since the measuring
chamber is distinctly defined by the bottomed cylindrical member
and the cover, the fluid can act on the vane wheel with high efficiency.
A plurality of ribs radially arranged around the pivot are formed
integrally on the respective inner surfaces of the bottom portion
of the cylindrical member and the cover. Thus, the efficiency of
the action of the fluid on the vane wheel can be improved further.
In this invention, moreover, the pivot rotatably supporting the
vane wheel in the center of the bottom portion of the bottomed cylindrical
member is removably fitted in the cylindrical member to be supported
thereby.
Accordingly, the casing does not require any fitting portion for
the pivot, and can be manufactured with improved facility. The pivot
can readily be replaced by removing it from the bottom portion of
the bottomed cylindrical member which is taken out of the measuring
chamber as it is.
The individual portions of the pivot, including a portion to support
the fit with the bottom portion of the cylindrical member, may be
formed integrally. Alternatively, a tip bearing portion, a shank
portion, and a support portion may be formed from separate materials
and then combined together.
Also, an extended head formed at the support portion may be fitted
in a spot facing groove formed in the bottom portion of the bottomed
cylindrical member so as to be securely held between the bottom
portion of the cylindrical member and the bottom surface of the
casing. The head and the spot facing groove may function as locking
means for the pivot if they are made rectangular.
The flow meter according to this invention basically comprises
a bottomed cylindrical member and a cover, and further comprises
as instrumental error adjusting means, instead of using the prior
art adjusting plates, narrow penetrating holes near the inlet and
outlet nozzles and means attached to the bottomed cylindrical member
for adjusting the opening areas of the penetrating holes. Thus,
the flow rate of an adjusting flow passing through the penetrating
holes are controlled for instrumental error adjustment. In this
case, the flow rate is adjusted instead of adjusting the flow resistance,
so that individual adjustments for forward and counter flows may
be less affected by each other, and can be performed with higher
accuracy.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a plan view of an indicator section of a prior art flow
meter;
FIG. 2 is a longitudinal sectional view of the prior art flow meter;
FIG. 3 is a cross-sectional view taken along line III--III of FIG.
2;
FIG. 4 is a longitudinal sectional view of a flow meter according
to an embodiment of this invention;
FIG. 5 is a cross-sectional view taken along line V--V of FIG.
4;
FIG. 6 is a partially cutaway disassembled view taken along line
VI--VI of FIG. 5 showing a bottomed cylindrical member and a cover;
FIG. 7 is a partially cutaway view taken along line VII--VII of
FIG. 6;
FIG. 8 is a plan view of the bottomed cylindrical member taken
along line VIII--VIII of FIG. 6;
FIG. 9 is a bottom view of the cover taken along line IX--IX of
FIG. 6;
FIG. 10 is a diagram for illustrating the positional relationships
between a vane wheel and nozzles;
FIG. 11 shows instrumental error curves of the flow meter of the
invention compared with those of the prior art flow meter for illustrating
the relationship between instrumental errors and flow quantity;
FIG. 12 is an enlarged view of a pivot bearing portion of the flow
meter shown in FIG. 4;
FIG. 13 is a bottom view of the portion shown in FIG. 12;
FIG. 14 is a longitudinal sectional view of a pivot shown in FIG.
12;
FIG. 15 is a cross-sectional view similar to FIG. 5 showing a modification
of an adjusting section of the flow meter of the invention; and
FIG. 16 is a side view of the bottomed cylindrical member taken
along line XVI--XVI of FIG. 15.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
There will now be described in detail an embodiment of this invention
with reference to the accompanying drawings.
In a flow meter according to the embodiment of the invention shown
in FIG. 4 a measuring chamber 33 with a cylindrical peripheral
wall 33a is defined between an inlet port 31 and an outlet port
32 formed in a casing 30. An integral bottomed cylindrical member
34 formed of synthetic resin is detachably fitted in the chamber
33 so as to be closely in contact with the peripheral wall 33a.
As seen from FIG. 6 the cylindrical member 34 is provided with
U-shaped inlet and outlet nozzles 36 and 37 which are formed in
a top edge 35a of a side wall portion 35 so as to correspond to
the inlet and outlet ports 31 and 32 respectively. A cover 38 is
put on the cylindrical member 34 positioned through the engagement
between projections 39 integral with the top edge 35a of the cylindrical
member 34 and indentations 40 in a peripheral flange portion 38a
of the cover 38. When the cover 38 is on the cylindrical member
34 the nozzles 36 and 37 are each in the form of a rectangular
penetrating hole.
Inside the cylindrical member 34 a vane wheel 41 with six rectangular
vanes 41a is rotatably supported by a pivot 43 which is mounted
on a center boss 42a of a bottom portion 42 of the cylindrical member
34. A supporting shaft 44 of the vane wheel 41 extends upward through
an opening in the center of the cover 38 and is fitted with a driving-side
magnet coupling 46 at the top portion. A driven-side magnet coupling
47 is connected to a measuring mechanism 48 so as to correspond
to the magnet coupling 46. The measuring mechanism 48 is connected
to an indicator section 50 including a counter 49. The indicator
section 50 visually indicates measurement results in the same manner
as the counterpart in the prior art meter shown in FIGS. 1 to 3.
In the flow meter of this invention, the rotation of the vane wheel
41 is transmitted to the measuring mechanism 48 by means of the
magnet coupling 47 and the measuring chamber side of the casing
30 under the measuring mechanism 48 is isolated from the space surrounding
the measuring mechanism 48 by a partition frame 51. Therefore, a
fluid in the measuring chamber 33 will never penetrate the space
around the measuring mechanism 48. Thus, this meter is what is called
a dry flow meter. It is to be understood, however, that this invention
may also be applied to the so-called wet flow meter shown in FIG.
2 in which the shaft of the vane wheel is connected directly to
the measuring mechanism. Accordingly, this portion of the meter
constitutes none of the features or essential points of the invention.
A meter section 52 including the partition frame 51 is screwed
into the casing 30 in a liquid-tight manner through the medium of
a seal 53 and can be removed from the casing 30 by unscrewing.
After the meter section 52 is removed, the cover 38 and the bottom
cylindrical member 34 can be detached.
A positioning projection 42b is formed integrally on the outside
of the bottom portion 42 of the cylindrical member 34 and an indentation
54 is formed in the bottom wall of the casing 30 so as to correspond
to the projection 42b. The fitting position of the bottomed cylindrical
member 34 relative to the casing 30 is determined by fitting the
projection 42b in the indentation 54 as shown in FIG. 4. The indentation
54 can be formed in the bottom wall of the casing 30 by simple machine
work.
As shown in FIG. 5 the inlet and outlet nozzles 36 and 37 are
formed aslant in the side wall portion 35 of the bottomed cylindrical
member 34 so as to extend tangentially to the rotating direction
of the vane wheel 41. The passages of the nozzles 36 and 37 are
long enough to allow the fluid to flow along their slanting courses.
For example, an effective nozzle length of 7 mm (measured along
the central axis of each nozzle) may be secured if the side wall
portion 35 is 5 mm thick.
Since the nozzles are thus formed in the cylindrical member 34
the inlet and outlet ports 31 and 32 of the casing 30 require no
specially accurate machine work. Moreover, the ports 31 and 32 may
be arranged in a simple straight line along an axis Z--Z, as shown
in FIG. 5 so that the casing 30 may be formed more easily than
in the case of the prior art construction shown in FIG. 3. The peripheral
wall 33a of the measuring chamber 33 requires no accurate machine
work, either.
The rectangular nozzles 36 and 37 are preferable to the conventional
circular nozzles for the following reason. Here let it be supposed
that the width and height of a rectangular nozzle N represented
by a full line in FIG. 10 are a and b, respectively, the diameter
of a prior art circular nozzle M represented by a broken line is
d, one end portions (outer end portions) of the openings of the
two nozzles are in alignment with the extreme end portion of the
vane 41a of the vane wheel 41 and the cross-sectional flow areas
of the nozzles are equal. In this case, if the rectangular nozzle
N is so elongate that its height b is approximate to the width of
the vane 41a, the distance l.sub.1 from the cross-sectional center
of the rectangular nozzle N to the center of rotation of the vane
wheel can be made longer than the distance l.sub.2 from the cross-sectional
center of the circular nozzle M to the rotation center of the vane
wheel. The point of action of the fluid flowing through the rectangular
nozzle N is located at the position corresponding to the distance
l.sub.1 while that of the fluid flowing through the circular nozzle
M is located at the position corresponding to the distance l.sub.2.
On account of the difference between the distances l.sub.1 and l.sub.2
therefore, the torque on the vanes in the rectangular nozzle N is
greater than that in the circular nozzle M.
Thus, if the cross-sectional flow area is fixed, the fluid can
act on the vanes more efficiently in the rectangular nozzle N than
in the circular nozzle M. Accordingly, if a given torque is applied
to the vanes, the rectangular nozzle can be used with shorter vanes
for the same effect than those vanes which are required for the
circular nozzle. Thus, the vanes can be reduced in size.
In this embodiment, penetrating holes 55 and 56 are formed in the
side wall portion 35 of the bottomed cylindrical member 34 in the
vicinities of the nozzles 36 and 37 respectively. The cross-sectional
area of each of the penetrating holes 55 and 56 is about 20% of
that of each nozzle. The penetrating holes 55 and 56 also correspond
to the inlet and outlet ports 31 and 32 respectively. The penetrating
holes 55 and 56 are each provided with a tapped hole 57 vertically
extending from the top edge 35a of the side wall portion 35 of the
bottomed cylindrical member 34. Round holes 58 are formed in the
flange portion 38a of the cover 38 put on the cylindrical member
34 individually corresponding to the tapped holes 57. Adjust screws
59 as restricting means are movably screwed into opening regions
of the penetrating holes 55 and 56 through the individual tapped
holes 57.
The penetrating hole 55 corresponding to the inlet port 31 in
conjunction with its corresponding screw 59 functions are a forward
flow adjuster for instrumental error adjustment of the so-called
forward flow, while the other penetrating hole 56 corresponding
to the outlet port 32 in conjunction with its corresponding screw
59 functions as a counter flow adjuster for instrumental error
adjustment of the so-called counter flow.
Where the fluid flows in the forward direction, as shown in FIG.
5 the main stream of the fluid introduced through the inlet port
31 enters the measuring chamber 33 through the inlet nozzle 36 as
indicated by a full-line arrow to rotate the vane wheel 41. At the
same time, a by-pass stream penetrates the measuring chamber 33
through the penetrating hole 55 as indicated by a broken-line arrow
to control the rotation of the vane wheel 41 thereby adjusting
the instrumental errors of the forward flow. Where a counter flow
is produced, on the other hand, the fluid flows from the outlet
port 32 into the measuring chamber 33 through the outlet nozzle
37 to rotate the vane wheel 41 reversely. In this case, the by-pass
stream enters the measuring chamber 33 through the penetrating hole
56 to control the reverse rotation of the vane wheel 41 thereby
adjusting the instrumental errors of the counter flow. The counter
flow may be produced, for example, when a large quantity of fluid
is consumed through some piping systems connected to the side of
the inlet portion 31 while the fluid consuming side, i.e., a tap,
connected to the outlet port 32 is off or closed.
The quantity of fluid flowing through the penetrating holes 55
and 56 for adjustment can readily be changed by suitably adjusting
the length of projection of the screws 59 by means of a screwdriver
or the like. Here the instrumental error adjustment is based not
on the method to control the flow resistance by the adjusting plates
as shown in FIG. 3 but on the method to control the flow quantity
by the by-pass stream. According to this method, forward-flow adjustment
in one penetrating hole exerts less influence on counter-flow adjustment
in the other. Since the adjusting mechanism can be attached to the
bottomed cylindrical member, the number of parts used in the meter
can be reduced for simpler construction and for the economy of space,
and also the adjusting capability can be improved further. In particular,
the instrumental error adjustment for counter flow, which has conventionally
been a problem, can be performed satisfactorily.
Among the instrumental error curves shown in FIG. 11 curves (A)
and (B) represent instrumental errors for forward and counter flows,
respectively, for this embodiment, and curves (C) and (D) represent
those for the prior art meter as compared with the change of flow
rate. The rate of fluid consumption or flow rate normally ranges
from 30 l/h to 1.5 m.sup.3 /h with use of a nominal diameter of
13 mm. In the case of the prior art meter, as seen from FIG. 11
the instrumental error for counter flow is as great as approximately
-10% throughout the substantially whole range of low rate if the
meter is so adjusted as to minimize the instrumental error for forward
flow. In this case, the instrumental error will not be improved
any more.
In the case of this embodiment, as seen from FIG. 11 the instrumental
error for counter flow can greatly be improved, and the instrumental
error curve for counter flow resembles that for forward flow.
As regards the instrumental error curves for forward flow, moreover,
curve (A) for this embodiment is more stable in linearity than curve
(C) for the prior art meter. Curve (C) indicates a negative error
in a range of 200 l/h to 600 l/h and a greater positive error than
that indicated by curve (A) in a range of 40 l/h to 100 l/h. Thus,
curve (C) lacks stability. The flow rate to produce an instrumental
error of -5% is 20 l/h for curve (A) and 28 l/h for curve (C). Thus,
the prior art meter is limited in the range of flow rate responsive
to the allowable instrumental error range of .+-.5%.
According to this embodiment, the combination of the unique adjusting
mechanism and the rectangular nozzles provides high measuring performance
which cannot be obtained with use of the circular nozzles and the
adjusting plates of the prior art meter.
In this embodiment, moreover, a plurality of ribs 60 and 61 are
formed integrally on the respective inner surfaces of the bottom
portion 42 of the bottomed cylindrical member 34 and the cover 38
as expressly shown in FIGS. 8 and 9. The ribs 60 and 61 are radially
arranged around the center of rotation of the vane wheel 41 so as
to fill up the narrow spaces left over and under the vane wheel
41 in the cylindrical member 34 as shown in FIG. 4. The ribs 60
and 61 give resistance to those flows of fluid which escape to the
spaces over and under the vane wheel 41 after entering the measuring
chamber 33 thereby positively directing the flows toward the vane
wheel 41. Thus, the fluid can more efficiently apply turning effort
to the vane wheel.
An experiment indicated that it is advisable to provide eight ribs
60 under the vane wheel 41 for higher resistance and six ribs 61
over the vane wheel 41 if the vane wheel 41 has six vanes.
Since the pivot 43 is attached to the boss 42a in the center of
the bottom portion 42 of the bottomed cylindrical member 34 it
is unnecessary to machine the casing 30 for fitting work.
A deep annular groove 62 is formed in the under surface of a center
boss portion retaining the supporting shaft 44 of the vane wheel
41. Thus, the vane wheel 41 is reduced in weight.
As shown in the enlarged view of FIG. 12 the pivot 43 is formed
of a tip bearing portion 43a directly supporting the vane wheel
41 a shank portion 43b, and a support portion 43c fitted in the
boss 42a in the center of the bottom portion 42 of the bottomed
cylindrical member 34 to be supported thereby. The support portion
43c is provided with an extended head 70 forming an end portion
of the pivot 43 and a large-diameter shank portion 71 continuous
with the head 70. Thus, the pivot 43 can be attached to and detached
from the boss 42a through the underside of the bottom portion 42
of the cylindrical member 34. Formed in the boss 42a are a shaft
hole 72 penetrating the boss 42a and a rectangular spot facing groove
73 surrounding the shaft hole 72 corresponding to the shape of
the support portion 43c. When the pivot 43 is attached to the boss
42a, therefore, the rectangular head 70 is fitted in the groove
73 to prevent the pivot 43 from rotating unexpectedly. Thus, the
pivot is positioned with respect to its rotating direction.
In the state that the cylindrical member 34 is fitted in the casing
30 the support portion 43c of the pivot 43 is held between the
bottom portion 42 of the cylindrical member 34 and the bottom surface
of the casing 30 so that the support portion 43c may securely be
retained in the boss 42a. Therefore, if the cylindrical member 34
is so designed that its bottom portion 42 is brought in contact
with the bottom surface of the casing 30 the large-diameter shank
portion 71 is fitted tightly in the shaft hole 72 so that the fit
of the support portion 43c may be somewhat loose.
The support portion 43c may readily be removed from the boss 42a
without damaging the same by tapping a suitable tool against the
top of the large-diameter shank portion 71 as indicated by arrow
P in FIG. 12.
The pivot 43 may be integrally formed from metal or wear-resistant
synthetic resin. Alternatively, it is possible to form the tip bearing
portion 43a, the shank portion 43b, and the support portion 43c
from ebonite or wear-resistant synthetic resin, from stainless steel
or phosphor bronze, and from synthetic resin, respectively, so that
the tip bearing portion 43a is pressed into the shank portion 43b,
and that the support portion 43c is formed integrally on the shank
portion 43b, as shown in FIG. 14. According to this construction,
materials best suited to the functions of the individual parts of
the pivot 43 can be selected.
Thus, the pivot is removably attached to the bottomed cylindrical
member of synthetic resin fitted in the casing. Accordingly, the
pivot can be replaced with ease, and the casing requires no machine
work for attachment of the pivot thereto.
FIGS. 15 and 16 show a modification of the instrumental error adjusting
mechanism. In this case, a circumferential groove 80 is formed in
the outer peripheral surface of the side wall portion 35 of the
bottomed cylindrical member 34 to cover nearly half the circumference
of the side wall portion 35. One end 80a of the groove 80 extends
close to the inlet nozzle 36 to correspond to the inlet port 31
while the other end extends close to the outlet nozzle 37 to correspond
to the outlet port 32. The casing 30 is provided with an outwardly
projecting boss portion 81. An adjust screw 83 is movably screwed
into a tapped hole 82 of the boss portion 81 so that the tip of
the screw 83 extends into the groove 80. A cap screw 85 is fitted
on the adjust screw 83 in a liquid-tight manner with the aid of
a gasket 84.
Although the greater part of the fluid led into the inlet port
31 flows into the inlet nozzle 36 the remaining part as an adjusting
flow enters the groove 80 and then escapes directly to the outlet
port 32. Accordingly, the flow rate of the adjusting flow can be
adjusted by manually controlling the length of projection of the
adjust screw 83 in the groove 80. Thus, the rate or quantity of
fluid flow entering the measuring chamber through the inlet nozzle
36 may be changed for instrumental error adjustment.
The advantage of this modification lies in that the instrumental
errors can be adjusted directly by external manual operation without
removing the meter section. |