Note: Descriptions are shown in the official language in which they were submitted.
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1 DETAILED DESCRIPTION OF VIE INVENTION
The present invention relates to a valve actuator
for a valve used in a gas pipe line and more particularly
to a valve actuator provided Wyeth line break device cap-
able of automatically closing a valve when the gas pressure
in the pipe line drops below a predetermined value, and
more specifically, to a valve actuator provided with a line
break system capable of automatically closing a valve when
the gas pressure of the pipe line drops at a reduction rate
greater than a predetermined reduction rate for a period ox
time exceeding a predetermined period of time.
BRIEF DESCRIPTION OF THE DRAWINGS
` FIGURE 1 is a representation showing the con-
stitution of an exemplary gas-hydraulic valve actuator
equipped with a conventional line break system; and
FIGURE 2 is a representation showing -the con-
stitution of the essential portion of a gas-hydraulic valve
actuator equipped with a line break system embodying the
present invention.
FIG. 1 is a representation of the constitution of
a conventional gas-hydraulic actuator employed in control-
lying a ball valve provided with a line break system and used
in a gas pipe line, shown by way of example.
In this gas-hydraulic actuator, the valve stem 3
of a ball valve assembly 2 incorporated into a gas pipe line
1 is turned through an angle of 90 at a fixed revolving
rate by the arm 31 of the Scotch yoke mechanism of -the
1 actuator assembly to open and close the valve. More specify
icily, the gas pressure of the pipe line us transmitted
to a pressure vessel 23 or 24 in response to a valve control
signal to pressurize the working fluid contained in the
pressure vessel and to send the pressurized working fluid
into the cylinder of the actuator for shifting a piston 32
and a piston rod 33, whereby the arm is turned in proportion
to the stroke of the piston rod. The position of the arm
in FIG. l corresponds to the open position of the ball
valve.
In order to transmit the gas pressure ox the
pipe line to the pressure vessel, an upstream position and
a downstream position, with respect to the valve assembly
2, of the pipe line are connected through stop valves 4
and 5 to a shuttle valve 13 by means of gas conduits 11
and 12 respectively and the shuttle valve 13 is connected
to a pair of 2-position solenoid valves 21 and 22 contained
in a housing 20 by a gas conduit 14. The solenoid valves
are shown in a neutral position in FIG. 1 where the port of
the gas conduit 14 is locked.
When a valve closing signal is applied to a term-
final 7, the solenoid 22s of the solenoid valve 22 is en-
ergized to shift the spool so that the gas conduit 14 is
connected through a shuttle valve 44 to a gas pressure-
controlled changeover valve 42 and also to a gas conduit
16 through its branch conduit aye. Consequently, the gas
pressure of the pipe line is transmitted through the gas
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1 conduits 14, aye and 16 to the pressure vessel I to pros-
Sirius the working fluid contained in the pressure vessel
24. The pressurized working fluid flows through a flow
control valve 26 and a changeover valve 27 into the
cylinder chamber 35 of the actuator assembly to shift the
piston and the piston rod ruptured, thus causing the arm
of -the Scotch yoke mechanism to turn the valve stem so that
the ball valve is closed.
In the other solenoid valve 21, when the solenoid
21s is energized, the gas pressure is transmitted through
a changeover valve 40 to a gas pressure-operated change-
over valve 41. Then similarly to the case of the sole-
nod valve 22, the gas conduit 14 is connected through gas
conduits 43b and 15 to the pressure vessel 23. Consequently,
the working fluid contained in the pressure vessel 23 is
pressurized and the pressurized working fluid is sent through
a flow control valve 25 and the changeover valve 27 to the
cylinder chamber 34 of the actuator assembly to shift the
piston rod left ward thus opening the valve.
- The constitution and the manner ox operation of
the conventional line break device will be described here-
inciter. A gas conduit 17 is connected through a stop
valve 6 to the pipe line. A gas conduit 18 branched Roy
the gas conduit 17 is connected through a restricting check
valve 50 to a sensing tank 51 to maintain the internal gas
pressure ox the sensing tank equal to the internal yes
pressure of the pipe line. The gas conduit 17 is connected
.
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1 both to the diaphragm chamber 54 of a diaphragm changeover
valve 53 equipped with a diaphragm 52 and to a port aye
connected to a gas conduit 56. Normally, the port aye is
blocked. Normally, the pressure in the diaphragm chamber
and the pressure at toe port aye are maintained equal to
the gas pressure in the pipe line. The secondary side of
the changeover valve 53 is connected -through a gas conduit
19 to the sensing tank.
In case the gas pressure in the pipe line is
reduced, the internal pressure of the diaphragm chamber of
the changeover valve 53 is reduced due to the direct con-
section of the diaphragm chamber to the pipe line f whereas
since the secondary side of the changeover valve is connected
to the sensing tank and the restricting check valve 50 is
interposed between the secondary side of the changeover
valve 53 an the pipe line, the reduction in the internal
pressure of the secondary side is small, and hence a differ-
entail pressure is produced between the diaphragm chamber
and the secondary side of the changeover valve 53. The
differential pressure causes the valve position of the
changeover valve 53 to change to the left valve position.
Consequently, the gas supplied from the gas conduit 17 to
the changeover valve 53 is supplied through the port aye,
the yes conduit 56 and the shuttle valve 44 to the change-
over valve 42. At the same time, the same gas pressure is
applied to the changeover switch 40 to change the valve
position thereof. Accordingly, the changeover valve 42
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I
l connects the gas conduits lo and aye to the conduit 16,
thus transmitting the gas pressure to the pressure vessel
I so that the working fluid contained in the pressure
vessel I is pressurized to close the valve.
However, since the reduction in the gas pressure
ill the pipe line is detected mechanically by means of the
diaphragm changeover valve 53 in the above-mentioned line
break system, the accuracy of detection is unsatisfactory,
and such a mechanical line break device is inappropriate
to a gas pipe line for a corrosive gas. Furthermore, in
some cases, it is desirable to close the valve only after
the predetermined duration ox gas pressure reduction in a
pipe line, and yet the above-mentioned line break system
employing a diaphragm changeover valve closes the valve
immediately after the gas pressure of the pipe line has
been reduced below a predetermined value.
- Accordingly, the present invention has been made
to solve those problems in the conventional line break
system. It is an object of the present invention to provide
an actuator for a valve equipped with a line break system
capable to operating accurately when the gas pressure in a
pipe line reduces below a predetermined value, and more
particularly, to provide a valve actuator for a valve
equipped with a line break system capable of operating only
after a predetermined duration of the reduction in the gas
pressure of a pipe line.
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,.
I
1 A valve actuator embodying -the prevent invention
comprises gas-hydraulic system, wherein solenoid valves
are connected through conduits to a gas pipe line, the
respective solenoids of the solenoid valves are energized
or ale energized to send -the gas flowing through the gas
pipe line directly to the corresponding cylinder chambers
of the valve actuator through the solenoid valves or to
send the gas to pressure vessels to pressurize the hydraulic
fluid contained in the pressure vessels thus causing the
pressurized fluid to be supplied to the corresponding
cylinder chambers, in order to drive the valve stem of
a valve incorporated into the gas pipe line so that the
valve is opened or closed, and a gas pressure detecting
device is provided to energize or de-energize the solenoids
of the solenoid valves in order to close the valve when the
gas pressure detected by the gas pressure detecting device
is below a predetermined gas pressure.
; the present invention will be described herein-
after in connection with the drawing illustrating a pro-
furred embodiment thereof
FIG. 2 shows a gas-hydraulic type valve actuator
embodying the present invention as applied to a ball valve.
In FIG. 2 part of the same constitution as -that shown in
FIG. 1 is omitted for simplicity and an additional con-
stitution according to the present invention is shown.
Accordingly, like elements or like constitutions are de-
signaled by like reference characters through FIGS. 1 and
2 and the functions of the elements or constitutions
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1 designated by the same reference characters are the same.
According to the present invention, a pressure
detecting device 60, for example, a pressure gauge, is
connected through a gas conduit 17 for the line break
system of a gas pipe line to a gas pipe line to detect the
gas pressure. The detected gas pressure is applied to a
controller 61. when -the detected gas pressure is below a
predetermined gas pressure, a control circuit 62 energizes
the solenoid 22s of a solenoid valve 22 to connect a gas
conduit connected to the gas pipe line to a gas conduit 16.
Consequently, as described herein before, the working fluid
contained in a pressure vessel is supplied through a flow
control valve 26 and a changeover valve to the cylinder
chamber 35 of an actuator/ thus closing the-valve.
In a preferable embodiment of the present invention,
the controller does not provide a command signal to energize
the solenoid of the solenoid valve unless the detected gas
pressure keeps decreasing at a rate greater than a prude-
termined rate of gas pressure reduction.
Another valve actuator embodying the present
invention comprises a gas-hydraulic system, wherein solenoid
valves are connected through conduits to a gas pipe line,
the respective solenoids of the solenoid valves are energized
or de-energized to send the gas flowing through the gas
pipe line directly to the corresponding cylinder chambers
of the valve actuator through the solenoid valves or to
send the gas to pressure vessels to pressurize the hydraulic
23~
1 fluid contained in the pressure vessels thus causing the
pressurized fluid to be supplied to the corresponding
cylinder chambers, ion order to drive -the valve stem of a
valve incorporated into the gas pipe line so -that the valve
it opened or closed, a gas pressure detecting device is
provided to detect the gas pressure in the gas pipe line,
and the respective solenoids of the solenoid valves are
adapted to be energized so that the valve is closed when
the detected gas pressure decreases for a predetermined
period of time at a rate greater than a predetermined rate
of reduction.
In the second embodiment ox the present invention, -
the valve is not closed immediately, but only upon the reduce
lion in the gas pressure; the reduction of the gas pressure
per unit time period, namely, gas pressure reduction rate,
is determined on the basis of the detected gas pressure and
the solenoid valve 22 is not actuated unless the measured
gas pressure reduction rate is greater than a predetermined
reduction rate and, in addition, the duration of gas pros-
sure reduction is longer than a predetermined time period.
Ordinary valve control operation, in which the
line break system is not used, by the valve actuator of the
present invention is carried out by applying a signal to
the terminal to energize the solenoid of the solenoid valve
21 or 22. For example, when the solenoid of the solenoid
valve 22 is energized by the agency of a circuit, not shown
in FIG. 2, the valve can be closed in the same manner as
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1 described hereinbe~ore. Furthermore, when the solenoid of
the solenoid valve 21 is energized, the conduit 14 connected
to the gas pipe line is connected to the conduit 15 to
open the valve.
although the present invention has been described
hereinhefore as applied to a valve actuator for a gas-
hydraulic ball valve, it is obvious that the present invention
is applicable not only to a ball valve, but also to a gate
valve, since a gate valve differs from a ball valve only
in respect of controlling the valve by raising or lowering
the valve stem connected to the valve element instead of
turning the valve stem as in a ball valve. Furthermore,
it is obvious that the present invention is applicable not
only to a gas-hydraulic valve actuator, but also to a gas-
operated valve actuator in which the gas flowing through
the corresponding pipe line is employed as a working fluid
for operating the valve actuator.
;: ..
