Abstrict The reciprocating piston positive displacement flow meter of the
present invention comprises a hollow flow tube having a movable
piston for reciprocal movement between opposite ends and a solenoid
controlled valve assembly having a sliding valve member for reversing
the direction of fluid flow through the flow tube in response to
the activation and deactivation of a solenoid. The solenoid is switched
from an activated state at one end of the piston stroke to an unactivated
state at the opposite end.
Claims What is claimed is:
1. A flow meter for the continuous measurement of fluid flow comprising:
(a) a hollow open ended flow tube having a movable piston disposed
therein for reciprocal movement between a first and second piston
position corresponding to the opposite ends of the piston stroke;
(b) a first flow path connected to said flow tube at one open end
thereof and a second flow path connected to said flow tube at the
opposite end thereof;
(c) a solenoid-controlled valve assembly comprising a sliding valve
member having opposite ends, a hollow interior extending between
said opposite ends and an opening connected to said interior at
each opposite end thereof; a valve body surrounding said sliding
valve member, with said valve body having a first and second end,
an inlet port located at said first end connected to said first
flow path, and an outer port located at said second end connected
to said second flow path, and a solenoid for reciprocating said
sliding valve member between said first and second ends of said
valve body, so as to align said inlet port with one opening of said
sliding valve member at one end thereof, when said sliding valve
member is adjacent the first end of said valve body, and for aligning
said outlet port with the opening in said sliding valve member at
its opposite end, when said sliding valve member is adjacent said
second end of said valve body;
(d) inlet and outlet means connected to said valve body for directing
and withdrawing a fluid stream through said valve body, with said
inlet means being connected through said sliding valve means to
said outlet port and said outlet means being connected to said inlet
port when said sliding valve member is moved to said second end
of said valve body, and with said inlet means being connected through
said sliding valve means to said inlet port and said outlet means
being connected to said outlet port when said sliding valve member
is moved to said first end of said valve body;
(e) means for detecting the presence of said piston at each of
said first and second positions, respectively; and
(f) means for activating and deactivating said solenoid to reverse
the movement of said sliding valve member in response to the detection
of said piston at each such piston position, respectively.
2. A flow meter, as defined in claim 1 wherein said solenoid comprises
an armature having a first and second section, an armature winding,
and spring means disposed between said first and second section,
with said second section of said armature being movable and engaging
said sliding valve means so as to cause said sliding valve means
to reciprocate in response to the energization and de-energization
of said armature winding.
3. A flow meter, as defined in claim 2 wherein said flow tube
is a precision bore cylindrical tube, and wherein said movable piston
is composed of graphite and is fitted with a tight tolerance in
said tube to establish substantially frictionless operation.
4. A flow meter, as defined in claim 3 wherein said fluid is air.
5. A flow meter, as defined in claim 4 wherein said means for
activating and deactivating said solenoid comprises a microcontroller
and solenoid driver.
Description FIELD OF INVENTION
This invention relates to a reciprocating piston positive displacement
flow meter for measuring fluid flow on a continuous basis.
BACKGROUND OF THE INVENTION
The measurement of gas flow is becoming increasingly more important
in the application and control of many processes as well as in the
research laboratory. One of the accepted instruments for gas flow
measurement and calibration is the bubble flow meter. In the basic
form of the bubble flow meter a soap film is generated from a soap
solution which is propelled by the gas flow under measurement from
one end of the flow meter to the other. By timing the rise of the
soap film between calibrated volume marks, the volume flow is obtained.
Although it is generally agreed that the bubble flow meter accuracy
may be affected by changes in ambient conditions such as humidity
and temperature and is dependent upon gas flow rate it is understood
that these factors can be readily corrected or compensated for in
a laboratory setting. This is not however, as easily done in a field
setting or in a commercial process environment. Moreover, the bubble
flow meter is a cumbersome and generally unwieldy instrument to
use as compared to a positive displacement piston type flow meter.
A reciprocating piston flow meter also provides a continuous output
reading independent of operator input and with a high degree of
measuring accuracy. Heretofore such a device required multiple valves
and an unwieldy valving arrangement.
SUMMARY OF THE INVENTION
The flow meter of the present invention utilizes a precision bore
cylindrical flow tube with a movable piston which is automatically
reciprocated from one end of the flow tube and back in a continuous
fashion by means of a solenoid controlled valve assembly having
a sliding valve member for reversing the direction of fluid flow
through the flow tube in response to the operation of a solenoid.
The fluid flow positive piston displacement flow meter of the present
invention comprises:
(a) a hollow flow tube having a movable piston disposed therein
for reciprocal movement between a first and second piston position
corresponding to the opposite ends of the piston stroke;
(b) a first flow path connected to said flow tube at one end thereof
and a second flow path connected to said flow tube at the opposite
end thereof;
(c) a solenoid-controlled valve assembly comprising a sliding valve
member having opposite ends, a hollow interior extending between
said opposite ends and an opening connected to said interior at
each opposite end thereof; a valve body surrounding said sliding
valve member, with said valve body having a first and second end,
an inlet port located at said first end connected to said first
flow path, and an outlet port located at said second end connected
to said second flow path, and a solenoid for reciprocating said
sliding valve member between said first and second ends of said
valve body, so as to align said inlet port with one opening of said
sliding valve member at one end thereof, when said sliding valve
member is adjacent the second end of said valve body, and for aligning
said outlet port with the opening in said sliding valve member at
its opposite end, when said sliding valve member is adjacent said
first end of said valve body;
(d) inlet and outlet means connected to said valve body for directing
and withdrawing a fluid stream through said valve body, with said
inlet member being connected through said sliding valve means to
said outlet port and said outlet means being connected to said inlet
port, when said sliding valve member is moved to said first end
of said valve body, and with said inlet means being connected through
said sliding valve means to said inlet port and said outlet member
being connected to said outlet port when said sliding valve member
is moved to said second end of said valve body;
(e) means for detecting the presence of said piston at each of
said first and second positions, respectively; and
(f) means for activating and deactivating said solenoid to reverse
the movement of said sliding valve member in response to the detection
of said piston at each such piston position, respectively.
BRIEF DESCRIPTION OF THE DRAWINGS
Other features and advantages of the present invention will become
apparent from the following detailed description of the invention
when read in conjunction with the accompanying drawings of which:
FIG. 1 is a partially schematic, partially diagrammatic view of
the flow meter of the present invention and the overall system for
measuring and displaying the measured fluid flow;
FIG. 2 is a view in vertical section of the solenoid controlled
valve assembly of Figure with the solenoid shown in the unactivated
state; and
FIG. 3 is a view similar to FIG. 2 with the solenoid shown in the
activated state.
DETAILED DESCRIPTION OF THE INVENTION
Referring now to FIG. 1 which illustrates the invention in terms
of providing a continuous output reading corresponding to the rate
of flow of a fluid being pumped by pump P from the atmosphere or
from any desired compressible fluid source. The flow meter (10)
comprises a hollow cylindrical precision bore open ended flow tube
(12) with a movable solid piston (14) composed of a material such
as graphite and disposed in the flow tube (12) with a tight tolerance
to establish a substantially frictionless operation. The movement
of the piston (14) is reversed continuously upon reaching a predetermined
position at each opposite end of the flow tube (12) which is detected
by a conventional set of photoelectric devices (1) and (2) respectively
under the control of a programmed microcontroller (70). The microcontroller
is a conventional special purpose microprocessor which upon receipt
of a detected signal from a receiver activates or deactivates the
solenoid control valve assembly (22) based on which receiver provides
the signal. Each set of photoelectric devices may consist of an
LED transmitter and receiver located at a given position along the
flow tube (12) corresponding to each end thereof at which the piston
(14) is to reverse direction.
The open ends of the flow tube (12) are connected to conduits (18)
and (20) which are, in turn, connected to the solenoid control valve
assembly (22). The solenoid control valve assembly (22) is connected
to a pump P through an inlet and outlet fitting (24) and (26) respectively.
As is more specifically shown in FIGS. 2 and 3 the solenoid controlled
valve assembly (22), comprises a valve body (30) and a sliding valve
member (32) in the form of a hollow tube of any desired composition.
The tubular sliding valve member (32) has openings (33 and 34) at
it's opposite ends for providing ingress and egress to and from
the hollow interior of the tubular member (32). A guide pin (36)
extends from one end of the sliding valve member (32) into sliding
engagement within a female bore (35) formed in the valve body (30).
The tubular sliding valve member (32) is attached at the opposite
end to the movable armature section (38) of the solenoid (28) for
movement in concert therewith. The solenoid (28) is a conventional
device having an armature winding (40) wound about an armature consisting
of the movable section (38) and a fixed section (42) separated by
a compression spring (41) located between the two armature sections
(38 and 42) respectively. The solenoid (28) has a mounting member
(43) press fitted into the cavity (31) of the valve assembly (22)
which is sealed by an o-ring (44).
The valve body (30) is coupled through port (45) to the conduit
(18) for providing direct communication to the flow tube (12) through
passageway (46) and is coupled through port (47) to the conduit
(20) for providing direct communication to the flow tube (12) through
passageway (48). Likewise the valve body (30) has ports (49) and
(50) communicating with the inlet and outlet fittings (24) and (26)
respectively.
A pair of sealing disks (52) and (54) are mounted over the sliding
valve member (32) for engaging valve seats (55 56 57 and 58) depending
upon the position of the sliding valve member (32). The valve seats
(56) and (57) are formed on an annuler insert (60) mounted to the
wall section (61) of the valve body (30). The valve seat (58) is
formed as an extension of the mounting member (43) attached to the
solenoid (28). The valve seat (55) extends from the wall section
(63) of the valve body (30). The annuler insert (60) forms a cylindrical
annulus (65) surrounding the tubular sliding valve member (32) which
is sealed against leakage by o-rings (66) and (67) respectively.
The operation of the solenoid control valve assembly (22) is best
understood by reference to the arrows in FIGS. 2 and 3 which identify
the direction of fluid flow through the valve body (30) for controlling
the direction of travel of the piston (14) in the flow tube (12).
As shown in FIG. 2 air is fed from the atmosphere through the inlet
fitting (24) into the cavity (31) of the valve body (30). The air
then flows into the tubular sliding valve member (32) through the
openings (33) and exits the tubular sliding valve member (32) through
the openings (34) into the passageway (48) of conduit (20). The
air stream proceeds into the open ended flow tube (12) as shown
in FIG. 2 from the right hand side thereof causing the piston (14)
to move from a position in line with the set of photoelectric devices
(2) toward the set of photoelectric devices (1). The piston (14)
forces an equal volume of air on the left hand side of the piston
(14) to travel through passageway (46) in conduit (18) past port
(45) into the cavity (31) from whence the air flows into the annulus
(65) and then through the port (50) into the outlet fitting (26)
back to the opposite side of the pump P. When the piston (14) reaches
the set of photoelectric devices (1) detected signal is transmitted
to the microcontroller (70). The micro-controller (70) delivers
an output signal to a solenoid driver (71) representing a power
amplifier for amplifying the signal from the microcontroller. The
amplified signal is fed to the armature coil of the solenoid (28)
for activating the solenoid (28) The micro-controller (70) is also
programmed to time the interval between detected signals from the
two sets of photoelectric devices (1) and (2) and to compute the
flow rate from such information as is well known to those skilled.
The micro-controller (70) also delivers a signal to the LCD driver
(72) to provide a continuous output reading (73).
Upon activating the solenoid (28) the movable armature section
(38) is moved into the cocked position against the fixed section
(42) with the compression spring (41) fully compressed as shown
in FIG. 3. In this position the air flow from the inlet fitting
(24) passes into the cavity (31) and passes directly into the passageway
(46) in conduit (18) through port (45) thereby reversing its direction
into the flow tube (12). The piston (14) is now forced to move from
the left hand side to the right hand side. An equal volume of air
is pushed into passageway (48) of conduit (20) which flows through
port (47) into cavity (31) and around the sliding valve member (32)
into the outlet fitting (26) through port (50). The piston (14)
will continue in this direction until its position is intercepted
by the set of photoelectric devices (2) at which time the solenoid
(28) is deactivated in response to a signal from the microcontroller
970) by means of the solenoid driver (71). Upon deactivation the
solenoid (28) releases the armature section (33) which returns to
its unactivated position as shown in FIG. 2 with the aid of the
compression spring (41). The piston (14) now repeats itself traveling
in the opposite direction toward the set of photoelectric devices
(1) as earlier explained. |