A slow flow meter having a free piston slideably mounted in a cylinder
with a non-contact type detector measuring movement of the same.
A bypass is provided between fluid inflow and outflow pipes connected
to opposite ends of the cylinder. A forcible returning device is
operatively associated with the bypass controller to return the
free piston to its original position after measurement.
What is claimed is:
1. A flow meter of the type that a displacement amount of a free
piston resulting from the same being moved in a cylinder by supplying
fluid thereinto is detected by a non-contact type detecting means
to measure a flow rate of the fluid, characterized in that there
is provided a bypass connecting between fluid inflow and outflow
pipes which are connected to both end portions of the cylinder;
and there is additionally provided a source of fluid to be measured
and a separate forcible returning means for returning the free piston
to its original position operated simultaneously with opening of
the foregoing bypass after the completion of an advancing stroke
of the free piston, said forcible returning means comprising a pump
interposed in the bypass; and in that the free piston is constructed
by a combination of a nonconducting material tubular body and a
conductive material end plate closing at least one end opening of
the tubular body.
2. A flow meter of claim 1 wherein the conductive material end
plate is combined with the end opening of the nonconducting material
tubular body by mounting the same under presssure therein or bonding
3. A flow meter of claim 1 wherein the free piston is a closed
4. A flow meter of claim 1 wherein each of the fluid inflow and
outflow pipes is provided with a swelled chamber midway of the same.
This invention relates to a flow meter wherein the amount of displacement
of a free piston movement in a cylinder resulting from supplying
fluid thereinto is detected by a noncontact type detecting means
to measure the flow rate of the fluid.
This free piston type flow meter is suitable for measuring a very
small flow rate because the meter is highly sensitive. This invention
has for its object to provide an improved flow meter of this type
wherein a free piston thereof is returned to its measuring starting
position immediately after the completion of a flow rate of fluid,
so that an improvement in the measuring efficiency thereof results.
Namely, it is the gist of this invention that there is provided
a bypass connecting between fluid inflow and outflow pipes which
are connected to both end portions of a cylinder, and there is additionally
provided such a forcibly returning means for returning the free
piston to its original position that the same is operated simultaneously
with opening of the foregoing bypass after the completion of an
advancing stroke of the free piston.
The above and other objects and the attendant advantages of the
present invention will become readily apparent by reference to the
following detailed description when considered in conjuction with
the accompanying drawings wherein:
FIG. 1 is a sectional side view of a first embodiment of this invention;
FIG. 2 is a sectional side view of a second embodiment of this
FIG. 3 is a sectional side view of a third embodiment of this invention;
FIG. 4 is a sectional side view of a fourth embodiment of this
FIG. 5 is an exploded perspective view of a free piston used for
any of the above embodiments thereof;
FIG. 6 is a side view, partly in section, of a modified example
of the free piston;
FIG. 7 is a sectional side view of another modified example of
FIG. 8 is an enlarged sectional view of a part thereof;
FIG. 9 is a sectional side view of further another modified example
of this invention, and
FIG. 10 is an exploded perspective view of a free piston used for
the example in FIG. 9.
Embodying examples of this invention will now be explained with
reference to the acompanying drawings:
Referring to FIG. 1 showing one example thereof, a cylinder 1 made
of a non-conducting material such as transparent glass or the like,
has both end openings closed by closure members 2 3. A free piston
4 is arranged to be slideably moved along and in the cylinder 1.
The free piston 4 is constructed having an end plate 4b made of
a conductive material such as aluminum or the like which serves
as a member to be detected. End plate 4b is fixedly mounted under
pressure in or bonded to one end opening of a tubular body 4a made
of a nonconducting material such as glass, ceramics, synthetic resin
or the like. FIG. 5 shows an exploded perspective view thereof.
A piston 4 with this construction is advantageous in that the same
is small in weight and has a high degree precision of a sliding
surface thereof in relation to the cylinder 1. As a result, the
flow meter is heightened in its sensitivity. The piston 4 may be
a closed hollow with both end openings of the tubular body closed
by end plates. Furthermore, the piston 4 may be constructed, as
shown clearly in FIG. 6 for instance, such that the tubular body
4a has both its end wall portions formed intergrally therewith as
a molding to form a closed hollow body made of non-conducting material.
The end plate 4b serving as a member to be detected is affixed to
the external surface of the end wall portion of the closed hollow
body. The piston 4 with such a closed hollow construction is advantageous
in that the same is bouyant and thereby friction between the lower
circumferential surface thereof and the inner circumferential surface
of the cylinder 1 can be decreased. Accordingly, the flow meter
can be further improved in its sensitivity.
A non-contact type detecting means 5 operable by eddy current is
provided on the inner surface of the closure member 2 so as to face
the end plate 4b of the foregoing piston 4 and is connected to
a signal convertor (not shown).
The closure members 2 3 are provided at their respective peripheral
portions with fluid inlet and outlet openings 8 9 which are in
communication with a front chamber 6 and a rear chamber 7 of the
cylinder 1 partitioned by the free piston 4.
The inlet and outlet opening 8 on the front chamber 6 side is connected
through a pipe 10 to a supply source of fluid to be measured (a
tank through a pump, for instance), and the inlet and outlet opening
9 on the rear chamber 7 side is connected through a pipe 11 to a
surge tank or the like.
The fluid in-flow and outflow pipes 10 11 are interconnected through
a bypass 12 which is in parallel with the cylinder 1 and a four
port connection valve 13 is provided in the bypass 12.
In place of the four port connection valve 13 an opening and closing
valve 13a used in examples as shown in FIG. 2 or 3 may be interposed
in the bypass 12.
In the example shown in FIG. 1 a forcibly returning means for
the piston 4 comprises a pump 14 which is interposed in the foregoing
bypass 12 between the valve 13 and pipe 10 via a pipe 20. In another
example shown in FIG. 2 the forcibly returning means comprises
an immersion pump 14a provided in the rear chamber 7 of the cylinder
1 and this arrangement is effective for making the flow meter small-sized
by utilizing a dead space in the cylinder.
If, under the condition that the four port connection valve 13
is set in the position shown by solid lines in FIG. 1 fluid is
supplied into the cylinder 1 the fluid flows into the front chamber
6 of the cylinder 1 through the pipe 10 and causes the free piston
4 to advance, and in the meanwhile, fluid previously contained in
the rear chamber 7 of the cylinder 1 is pushed out by the advancing
piston 4 and flows into the pipe 11 through the four port connecting
A voltage generated at the detecting means 5 rises according as
the piston 4 is advanced, and thus the raised voltage can be considered
as a displacement amount of the piston 2. Accordingly, the flow
rate can be obtained from the displacement amount of the piston
4 and the time taken for the displacement.
If the piston 4 is moved to reach the advancing end and the measuring
ends, the four port connection valve 13 is changed over counterclockwise
to the position shown by chain lines in the same Figure and the
pump 14 is operated, whereby the fluid is forcibly flowed into the
rear chamber 7 in the opposite flowing direction at the time of
measuring, and simultaneously the fluid in the front chamber 6 is
drawn out, whereby the piston 4 is returned to its original position.
During this returning operation, the pipes 10 11 are connected
one another through the bypass 12 and the valve 13 so that a main
current of the fluid continues to flow, though a flow of diverged
current thereof through the cylinder 1 is interrupted.
The four port connection valve 13 and the pump 14 may be synchronously
operated and synchronously stopped by using high and low values
of the output voltage of the detecting means 5 as respective control
Similarly, to the relation between the pump 14 and the valve 13
in the example of FIG. 1 the immersion pump 14a also in the example
of FIG. 2 may be operated and stopped synchronously with a changeover
operation of the valve 13a.
In another example shown in FIG. 3 the forcibly returning means
comprises a piston push rod 14b arranged to be driven by an electromagnetic
type linear reciprocating motion machine 15. At the time of measuring,
the push rod is retreated against the action of a compression coil
spring 16 as illustrated, and when the piston 4 reaches the advanced
end, the electromagnetic type linear reciprocating motion machine
15 is de-energized synchronously with the opening of the bypass
12 caused by a changeover operation of the opening and closing valve
13a, whereby the push rod 14b is extended by expansion of the spring
16 and pushes back the piston 4. Such a modification can be considered
that the foregoing linear reciprocating motion machine 15 can have
an air pressure cylinder or an oil pressure cylinder as a power
In another example shown in FIG. 4 the piston push rod 14b is
driven by a rotary reciprocating motion machine 17 which is a rotary
solenoid, a rotary cylinder, or the like. A cylindrical cam 18 has
a cam groove 18a for converting a rotary movement into a linear
movement. A pin 19 on the rear end of the push rod 14b is in engagement
with the cam groove 18a.
Further, in the example shown in FIG. 4 a shaft of the machine
17 and an operation shaft of the valve 13 or 13a are interconnected
directly one with another so that the two members may operate together
in such a manner that when the valve 13 or 13a is in its closed
position, that is, at the time of flow rate measuring, the piston
push rod 14b is advanced and when the valve 13 or 13a is in its
open position, the push rod 14b is extended to push back the piston.
Thus, according to this invention, in the free piston type flow
meter using the non-contact type detecting means, there is provided
the bypass 12 connecting between the fluid in-flow and outflow pipes
10 11 connected to the opposite end portions of the cylinder 1
and there is additionally provided such a forcible returning means
14 (14a, 14b) for returning the piston 4 to its original position
that is arranged to be operated simultaneously with opening of the
bypass 12 after the completion of the advancing stroke at the piston
4. In this manner, the piston 4 can be returned to its measuring
starting position immediately after the completion of measuring
of the flow rate. Thus, the measuring efficiency can be improved
in comparison with that of a conventional device wherein the piston
is returned only by a flowing force of the fluid caused by switching
the supply direction of the fluid in relation to the cylinder between
the front and the rear. Additionally, the fluid flow is not given
any external disturbance, and the sensitivity is improved.
Any of the foregoing examples of this invention flow meter can
be modified as shown in FIGS. 7 and 8. Namely, the fluid inflow
and outflow pipes 10 11 can be provided with respective swelled
chamber 21 22 formed at the portions thereof. With this arrangement,
the fluid current flowing through each pipe is lowered in its flow
rate at the interior of each chamber 21 or 22. Consequently, dust
or particles contained in the fluid drop by gravity and also bubbles
contained therein rise to the surface to be separated from the fluid.
In this manner, dust or bubbles which might be introduced into the
cylinder can be eliminated and the cylinder 1 can be always kept
clean, whereby the piston 4 can operate smoothly, resulting in improvement
in the sensitivity thereof.
An obstruction plate 23 is provided in each chamber 21 22 so as
to face the flowing direction of the fluid, and a bubble removing
plug 24 is provided at the top and a dust removing plug 25 is provided
at the bottom. The obstruction plate 23 is fixed by a stay not illustrated.
FIGS. 9 and 10 show another modified example of this invention
flow meter. In this example, the non-contact type detecting means
5 is provided on each end of the cylinder 1 so as to face the member
4b to be detected on each end surface of the piston 4 and the two
detecting means 5 5 are so arranged that a metering signal may
be obtained by a composition of their outputs generated simultaneously.
Thus, the detecting sensitivity in relation to the displacement
of the piston is amplified, so that a good sensitivity can be obtained
even if the displacement amount and the displacement speed of the
piston are small in relation to the diameter thereof. Accordingly,
this arrangement is especially suitable for the flow meter for measuring
a very small flow rate requiring a high sensitivity.
It is readily apparent that the above-described slow flow flow
meter meets all of the objects mentioned above and also has the
advantage of wide commercial utility. It should be understood that
the specific form of the invention hereinabove described is intended
to be representative only, as certain modifications within the scope
of these teachings will be apparent to those skilled in the art.
Accordingly, reference should be made to the following claims in
determining the full scope of the invention.