Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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TITLE OF lNVh~llON
AUTOMATIC CHAN~V~K MANIFOLD
FIELD OF lNV~.~lON
The present invention relates to an automatic
changeover manifold, particularly for use with cryogenic
fluids.
BACKGROUND TO l'~h INVENTION
Automatic changeover manifolds are extensively
utilized by the user of various gases where the supply
is from cylinders or banks of cylinders and where the
requirement is such that the flow must continue
uninterrupted when one of the cylinders or banks becomes
exhausted.
Examples of such operations in common usage are
welding operations and breathing and anaesthetic gas
flows in hospital environments. Most automatic
changeover manifolds (ACM) utilize specialized
changeover valves of the diaphragm type or regulators
using rubberized diaphragms, set to different pressures,
so that changeovers can occur and specialized 4-way
valves configured to semi-automatic operation. Such
conventional systems are not capable of controlling the
flow of cold cryogenic liquified gas.
A search with respect to the present invention has
been conducted in the facilities of the U.S. Patent and
Trademark Office and the following U.S. Patents have
been noted as the most relevant:
3,001,541 2,714,292
2,547,823 2,402,187
4,341,234 4,597,406
3,583,421 3,013,573
Of these references, U.S. Patent No. 2,402,187 is
considered to be the most pertinent as is discussed in
detail below. None of the cited prior art describes the
handling of cold cryogenic liquid gases but generally
,~
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disclose systems for maintaining the uninterrupted flow
of gases.
U.S. Patents Nos. 2,547,823 and 3,001,541
specifically illustrate the use of diaphragm-controlled
valves. U.S. Patent No. 2,714,292 requires a manual
reset when an exhausted supply is replenished. U.S.
Patent No. 3,013,573 describes the control of flow of
chemicals to a chemical stabilizing operation using
"conventional pressure switches" i.e. diaphragmed
switches. U.S. Patent No. 3,583,421 describes a
particular valve structure for use in a hospital
anaesthetic supply system. U.S. Patent No. 4,341,234
describes an acetylene supply system which is adapted to
achieve an improved gas utilization. U.S. Patent No.
4,597,406 describes a system for delivering high purity
gas at constant pressure using a particular switching
control system.
U.S. Patent No. 2,402,187, the closest known art,
describes an automatic control system for four acetylene
generators, arranged in two independent groups of two
generators each. The electrical circuit is divided into
two independent and identical circuits, so that
description of the operation of one pair of the
generators only is necessary.
As the supply of acetylene from one generator
declines sufficiently that the pressure produced falls
below a predetermined minimum value, the pressure switch
associated with that flow line is activated and closes a
pair of contacts, which causes an alarm to sound and a
visual signal to appear on the control panel to indicate
that the generator is inoperable and requires
recharging. Closing of the contacts by the pressure
switch also energizes one coil of a two-coil relay,
which then opens normally-closed switch contacts and
closes normally-open switch contacts. This activity
causes the motor-driven valve associated with the first
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generator feed line to close and the motor-driven valve
associated with the second generator feed line to open,
so that the second generator comes on-stream.
The opening of the normally-closed switch contacts
and the closing of the normally-open switch contacts
also causes a visual indicator that the one generator is
on-line to be extinguished and a visual indicator that
the other generator is now on-line to be lit. The alarm
is disabled by a manual reset switch. The first
generator is recharged and, when the second generator
becomes exhausted, the procedure is reversed.
It is evident, therefore, that the two-coil relay
and associated contacts act as an interconnected control
mechanism for the flow valves, constructed and arranged
such that when either generation unit is on-stream, the
other is cut off.
A draw-back to this prior art system, and one
overcome in the present invention, is that, if both
generators are inoperative at the same time, so that
both pressure switches are closed, it is necessary to
open manually a push button to prevent recycling of the
relay. Otherwise, the circuits through the relay coils
will be alternately made and broken in continuous cycles
as the switch contacts are alternately opened and
closed. In the present invention, in the absence of gas
flow, the system assumes a stand-by mode, without the
necessity for manual intervention.
SUMMARY OF lNv~.llON
In accordance with the present invention, there is
provided an apparatus for providing a continuous supply
of fluid to a fluid delivery conduit means. The
apparatus includes first and second fluid supply conduit
means for connecting respective first and second sources
of the fluid to the fluid delivery conduit. Each of the
fluid supply conduit means has pressure sensing means
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operatively connected thereto for sensing fluid flow
pressure and solenoid-operated on-off fluid flow control
valve means operatively connected thereto downstream of
the pressure sensing means for controlling fluid flow
therein.
The apparatus includes an electrical circuit which
controls the operation of the solenoid valves to switch
them on and off, so as to permit or prevent fluid flow
through the respective fluid supply conduit means. With
both fluid sources available, the electrical circuit
only permits one of the fluid sources to provide fluid
flow at one time while the electrical circuit is
activated.
When one of the fluid sources delivers fluid at a
pressure below a predetermined minimum value, the
electrical circuit generates a signal to close the
solenoid valve in the flowing fluid supply conduit and
simultaneously open the solenoid valve in the other
fluid supply conduit, so that fluid flow then commences
through that conduit to the fluid delivery conduit
means.
The exhausted fluid supply then can be replaced.
When replaced, the electrical circuit recognizes that
sufficient fluid pressure is now available but does not
activate fluid flow until the pressure in the other
fluid supply conduit falls below the predetermined
minimum valve.
If the exhausted fluid supply is not replaced and
the other fluid supply becomes exhausted, the electrical
circuit generates an electrical signal to close the
solenoid valve in the flowing fluid supply conduit, and
thereby both solenoid valves are in a closed-condition.
An alarm is activated to alert an operator to this
condition. The system remains on stand-by until one or
other of the exhausted fluid supplies is replaced,
whereupon fluid flow commences from the replenished
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supply.
This arrangement is completely different from that
described in the above-mentioned U.S. Patent No.
2,402,187, where it is necessary to manually switch off
the electrical circuit when both fluid supplies are
exhausted.
BRIEF DESCRIPTION OF DRAWINGS
Figure 1 is a schematic representation of an
automatic changeover manifold provided in accordance
with one embodiment of the invention; and
Figure 2 is a schematic representation of the
electrical control circuit for the manifold of Figure 1.
DESCRIPTION OF PR~KK~U EMBODrMENT
Referring to the drawings, an automatic changeover
manifold 10 comprises two identical halves. The
illustrated device 10 is intended to ensure
uninterrupted flow of fluid to a delivery conduit 12 by
switching between alternate left and right hand fluid
supplies, so that when one of the supplies is depleted,
the other automatically comes on stream. The depleted
supply can be replaced with fresh supply.
The apparatus 10 is particularly adapted for
handling cryogenic liquids, such as liquid nitrogen or
argon, but the principles thereof may be used to achieve
a continuous supply of any convenient fluid.
For each half of fluid supply system, there is
provided a port 14 connected to the supply of fluid to
permit fluid to flow through a conduit 16 to the
junction point 18 with the delivery conduit 12. Tapped
into the conduit 16 is a cluster 19 of a pressure sensor
20, pressure indicator 22 and pressure relief valve 24.
The cluster 19 may be tapped into the conduit 16 via a
thin copper tubing 26, which permits cryogenic gas
flowing in the conduit 16 to be warmed up to near
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ambient temperature, whereby the sensing and measuring
devices can operate in a normal temperature environment.
Positioned downstream of the cluster 19 in the
conduit 16 is a solenoid-operated valve 28, which may be
normally-open or normally-closed, depending on the
intended use, as discussed below, and a one-way, non-
return valve 30.
Downstream from the junction point 18 in the
delivery conduit 12 is positioned a pressure relief
valve 32, so that pressure build-up from any cryogenic
liquid trapped between closed valves can be safely
relieved. The pressure relief valves 24 serve a similar
function, as well as providing over-pressure protection
for the gauges 22 and pressure sensors 20.
An electrical control circuit 34 for the automatic
changeover manifold 10 is shown in Figure 2. The
electrical circuit 34 is protected by a circuit breaker
36. Power to the electrical circuit 34 is provided by
an ON-OFF switch 38 and a signal light 40 indicates the
state of the circuit (i.e. lit if powered and not lit if
not powered). When both banks of source fluid are full
and the power initially turned on, the contents of the
left or right bank, but not both, commence to flow to
the junction point 18 and thence to the delivery conduit
12. The signal lights 40 may have any desired colour,
for example, amber.
"Bank Empty" 42 lights are extinguished and the
respective flowing signal light 44 is lit, indicating
which of the banks is flowing. The "bank empty" lights
42 may be of any distinctive colour, such as red, and
the "bank flowing" lights 44 similarly may be of any
distinctive colour, such as green. "Select"
momentarily-off push button switches 46 are provided to
permit manual selection of the desired bank.
Control relays 48 energize or de-energize the
respective solenoid control valves 28 and the respective
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"flowing" signal light 44, indicating which bank of
fluid is flowing, through relay contacts 49 and solenoid
coils 51. The control relays 48 include anti-
coincidence contacts 50, so that only one bank at one
time can be flowing.
An exception to the latter arrangement is when
normally-open solenoid valves 28 are used, such as in
hospital use, so that, upon power failure, both solenoid
valves 28 open, thereby providing uninterrupted maximum
available supply.
As a flowing bank becomes exhausted, its pressure
drops. When the delivered pressure reaches a
predetermined minimum value, the pressure sensor 20
generates an electrical signal which opens the
lS respective switch 52, thereby de-energizing its
respective control relay 46 and providing lighting power
to a respective "bank empty" signal light 42.
Since the pressure switch 52 associated with the
other bank already is closed, since that bank is full,
20 opening of the circuit for the first bank and hence de-
energization of the anti-coincidence contacts 50, then
energizes the control relay 48 for the second bank, to
open the solenoid-operated valve 28 for the other bank
to permit fluid to flow from that bank to the junction
25 point 18. The flow indicating light 44 is illuminated.
At the same time, the solenoid operated valve 28 for the
exhausted bank is closed.
The first bank then can be replenished, in which
case, the pressure switch 52 for the first bank is again
30 closed and the respective "bank empty" light 42
extinguished. The non-return valve (30) permits the
empty bank to be removed and a full bank to replace it
without any loss of fluid and without the necessity to
cease operation. Flow of fluid from the replenished
35 bank is prevented from occurring by the anti-coincidence
contacts 50 until the second bank is exhausted.
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If both banks become exhausted, then both pressure
switches 52 are open (as illustrated in Figure 2), and
both "bank empty" lights 42 are lit. Both control
relays 48 become closed, which then activates an audio
alarm 54, to sound an alarm condition. When a full bank
is reconnected to one of the ports 14, the appropriate
pressure sensor 20 will sense the presence of fluid
pressure, close the respective pressure switch 52,
thereby energizing the respective control relay 48,
which opens the respective solenoid-controlled valve 26,
thereby recommencing fluid flow, and shuts off the alarm
54.
After the switch-over from one cylinder bank to the
other occurs and the empty bank of cylinder is not
immediately replaced, the empty bank of cylinders tends
to warm up and rebuild sufficient pressure to extinguish
the "bank empty" indicator light. To avoid this
problem, a solenoid valve 56 with its coil 58 are
provided in parallel with the respective bank empty
light 42 so as to be activated when the empty bank is
switched out of the circuit, so that the overpressure
resulting from warming-up of the cylinder bank can
continue to drain through a small orifice 60 and assure
signal reliability.
The electrical circuit 34, therefore, uses two
identical parallel circuits, each having a pressure-
activated switch 52 to activate the control relay 48 for
the specific solenoid-activated valve 28, with anti-
coincidence relay contacts 50 being employed to ensure
that only fluid from one bank flows to the delivery
conduit 12 at one time, to ensure that, when the
detected pressure of fluid delivered by one bank falls
below a predetermined level, there is immediately
commenced flow from the other bank to ensure an
uninterrupted supply, and to ensure that the system
assumes a stand-by mode if both banks become exhausted.
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In contrast to the prior art of U.S. Patent
No. 2,402,187 discussed above, it is not necessary to
shut-off the power to the control circuit 34 when both
banks are empty. The arrangement of the present
invention starts up immediately from the stand-by
position without manual intervention when a full bank of
fluid tanks is connected to a port 14. The arrangement
described above, not only identifies that an exhausted
bank exists, as in the cited prior art, but also which
of the banks is exhausted, by employing separate "bank
empty" lights 42. In addition, the system of the
present invention is able to provide an uninterrupted
supply in the event of power failure, for example, in a
hospital environment, by employing normally-open
solenoid valves 28.
SUMMARY OF DISCLOSURE
In summary of the disclosure, the present invention
provides a novel automatic changeover apparatus which is
useful for a wide variety of fluids, including cryogenic
fluids. Modifications are possible within the scope of
this invention.
