U.S. patent application number 12/718653 was filed with the patent office on 2010-10-21 for system and method for fire protection system corrosion mitigation.
This patent application is currently assigned to South-Tek Systems. Invention is credited to Timothy S. Bodemann.
Application Number | 20100263882 12/718653 |
Document ID | / |
Family ID | 42980140 |
Filed Date | 2010-10-21 |
United States Patent
Application |
20100263882 |
Kind Code |
A1 |
Bodemann; Timothy S. |
October 21, 2010 |
SYSTEM AND METHOD FOR FIRE PROTECTION SYSTEM CORROSION
MITIGATION
Abstract
An inert gas Fire Protection System (FPS) uses an inert gas
rather than air in a dry or pre-action type FPS. The inert gas
inhibits oxidation, galvanic corrosion, and/or bacterial growth,
and hence mitigates Microbiologically Influenced Corrosion (MIC)
and galvanic corrosion in the FPS piping. A zone purging valve,
which may include a gas purity analyzer, is disposed at the end of
each zone in the FPS. A controller over-pressurizes the FPS with
inert gas, and bleeds the gas through the zone purging valves to a
predetermined supervisory pressure. The pressurize/purge cycle is
repeated to ensure inert gas of a predetermined purity level
reaches all areas within the FPS. The purity of the inert gas is
periodically measured in bleed operations. The inert gas may
comprise Nitrogen, which additionally dries out residual water in
the FPS due to a low dew point, further inhibiting MIC.
Inventors: |
Bodemann; Timothy S.;
(Raleigh, NC) |
Correspondence
Address: |
COATS & BENNETT, PLLC
1400 Crescent Green, Suite 300
Cary
NC
27518
US
|
Assignee: |
South-Tek Systems
Raleigh
NC
|
Family ID: |
42980140 |
Appl. No.: |
12/718653 |
Filed: |
March 5, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61169974 |
Apr 16, 2009 |
|
|
|
Current U.S.
Class: |
169/17 ;
137/15.04; 137/455; 73/40.7 |
Current CPC
Class: |
Y10T 137/7897 20150401;
Y10T 137/0419 20150401; F16K 15/04 20130101; A62C 35/68 20130101;
A62C 35/62 20130101; G01M 3/2815 20130101; Y10T 137/7722
20150401 |
Class at
Publication: |
169/17 ;
137/15.04; 137/455; 73/40.7 |
International
Class: |
B08B 5/00 20060101
B08B005/00; A62C 35/00 20060101 A62C035/00; F16K 17/00 20060101
F16K017/00; G01M 3/20 20060101 G01M003/20 |
Claims
1. A method of inhibiting corrosion in fire protection system
piping, comprising: hydro-testing the fire protection system;
draining water from the fire protection system piping; purging
oxygen in the fire protection system piping by replacing it with an
inert gas; and maintaining the inert gas in the fire protection
system piping at a predetermined supervisory pressure and at a
predetermined purity level.
2. The method of claim 1 further comprising removing residual water
remaining in the FPS after draining.
3. The method of claim 2 wherein removing residual water comprises
introducing a low dew point gas into the fire protection system
piping; allowing the residual water to evaporate into the gas; and
purging the gas from the fire protection system piping.
4. The method of claim 1 wherein the inert gas is nitrogen.
5. The method of claim 1 wherein purging oxygen in the fire
protection system piping by replacing it with an inert gas
comprises (a) purging the oxygen in the fire protection system
piping with inert gas; (b) pressurizing the fire protection system
piping with inert gas at a pressure in excess of the predetermined
supervisory pressure; (c) bleeding the inert gas from the fire
protection system piping into one or more gas analyzers; (d)
repeating steps (b) and (d) until the inert gas reaches the
predetermined purity level.
6. The method of claim 1 wherein maintaining the inert gas in the
fire protection system piping at a predetermined supervisory
pressure and at a predetermined purity level comprises monitoring
the inert gas pressure and introducing inert gas into the fire
protection system piping if the pressure falls below the
predetermined supervisory pressure.
7. The method of claim 6 wherein monitoring the inert gas pressure
further comprises triggering one or more alarms if the inert gas
pressure is detected below the predetermined supervisory
pressure.
8. The method of claim 7 wherein a first alarm is triggered if less
than a first volume of inert gas is required to maintain the inert
gas pressure at the predetermined supervisory pressure within a
predetermined duration.
9. The method of claim 8 wherein a second alarm is triggered if
more than the first volume but less than a second volume of inert
gas is required to maintain the inert gas pressure at the
predetermined supervisory pressure within the predetermined
duration.
10. The method of claim 9 wherein a third alarm is triggered if
more than the second volume of inert gas is required to maintain
the inert gas pressure at the predetermined supervisory pressure
within the predetermined duration.
11. The method of claim 1 wherein maintaining the inert gas in the
fire protection system piping at a predetermined supervisory
pressure and at a predetermined purity level comprises periodically
bleeding inert gas through one or more gas analyzers to monitor the
purity of the inert gas.
12. A fire protection system, comprising: piping operative to carry
water over areas to be protected from fire; one or more sprinkler
valves operative to discharge water when a fire is detected; an
inert gas control system in gas flow relationship with the piping
and operative to selectively inject inert gas from an inert gas
source into the piping, and further operative to monitor and
control the pressure of the inert gas in the piping; and one or
more analyzing vents in gas flow relationship with the piping,
disposed remotely from the inert gas control system, and operative
to controllably vent gas from the piping and further operative to
analyze the purity of the vented gas.
13. The system of claim 12 wherein the analyzing vents are
additionally connected in control relationship to the inert gas
control system, and wherein the inert gas control system is further
operative to control the analyzing vents' operation.
14. The system of claim 12 wherein the analyzing vents are further
operative to report the measured purity of vented gas to the inert
gas control system.
15. The system of claim 14 wherein the inert gas control system is
operative to control both the pressure and purity of inert gas in
the piping by periodically controlling one or more analyzing vents
to vent inert gas and measure its purity; receiving a report of the
vented gas purity from the analyzing vents; and selectively inject
inert gas from the source into the piping, in response to the
pressure and purity of inert gas in the piping.
16. The system of claim 12 wherein the inert gas is nitrogen.
17. The system of claim 16 wherein the inert gas source comprises
one or more pressurized nitrogen tanks.
18. The system of claim 16 wherein the inert gas source comprises a
nitrogen generator operative to generate nitrogen from air.
19. The system of claim 12 wherein the inert gas control system is
further operative to trigger one or more alarms in response to the
inert gas pressure in the piping.
20. A method of assessing the leak rate in a Fire Protection System
(FPS) comprising a plurality of pipes operative to carry water,
comprising: affixing a pressure transducer in pressure sensing
relation to the FPS; linking the pressure transducer in data flow
relation to a data logger; pressurizing air in the FPS piping to a
predetermined supervisory pressure; recording the drop in air
pressure in the FPS piping, from the predetermined supervisory
pressure, as a function of time; and calculating the air pressure
leak rate of the FPS.
21. The method of claim 20 wherein affixing a pressure transducer
in pressure sensing relation to the FPS comprises affixing the
pressure transducer to an existing test port that includes a ball
valve.
22. The method of claim 20 wherein affixing a pressure transducer
in pressure sensing relation to the FPS comprises affixing the
pressure transducer to an existing supervisory pressure air
compressor accumulator tank.
23. The method of claim 20 wherein linking the pressure transducer
in data flow relation to a data logger comprises connecting the
pressure transducer to the data logger via a wired connection.
24. The method of claim 20 wherein linking the pressure transducer
in data flow relation to a data logger comprises connecting the
pressure transducer to the data logger via a wireless
connection.
25. The method of claim 20 wherein the pressurizing step is
repeated as the FPS pressure drops to a predetermined trigger
pressure.
26. The method of claim 25 wherein the recording step continues
over a predetermined duration, during which the pressurizing step
may be repeated a plurality of times.
27. A gas purging valve operative to be connected to piping in a
Fire Protection System (FPS) and to bleed gas at a predetermined
rate, comprising: an inlet in gas flow relationship with the FPS
piping; a central passage in gas flow relationship with the inlet;
a calibrated orifice removeably disposed in the central passage, in
gas flow relationship with the passage and operative to allow a
maximum predetermined gas flow rate therethrough; an outlet in gas
flow relationship with the calibrated orifice; and a ball disposed
upstream of the central passage, the ball operative to allow gas
flow through the gas purging valve but operative to impede the flow
of water through the gas purging valve.
28. The valve of claim 27 further comprising an o-ring disposed
upstream of the central passage, the o-ring sized and positioned
such that water pressure at the inlet urges the ball against the
o-ring, sealing the central passage against water flow
therethrough.
29. The valve of claim 28 wherein the ball and the o-ring are
disposed in the inlet.
30. The valve of claim 27 wherein the outlet is adapted to be
connected to a gas purity analyzer.
Description
[0001] This application claims priority to U.S. Provisional Patent
Application Ser. No. 61/169,974, titled, "The
MICBIast.TM.--Corrosion Inhibiting System for Fire Protection
Systems (FPS)," filed Apr. 16, 2009, the disclosure of which is
incorporated herein by reference in its entirety.
FIELD OF THE INVENTION
[0002] The present invention relates generally to fire suppression
systems, and in particular to a system and method to inhibit or
prevent Microbiologically Influenced Corrosion and galvanic
corrosion in dry or pre-action fire suppression systems.
BACKGROUND
[0003] Fire sprinkler systems are a well-known type of active fire
suppression system. Sprinklers are installed in all types of
buildings, commercial and residential, and are generally required
by fire and building codes for buildings open to the public.
Typical sprinkler systems comprise a network of pipes, usually
located at ceiling level, that are connected to a reliable water
source. Sprinkler heads are disposed along the pipes at regular
intervals. Each sprinkler head includes a fusible element, or a
frangible glass bulb, that is heat-sensitive and designed to fail
at a predetermined temperature. Failure of the fusible element or
glass bulb opens an orifice, allowing water to flow through the
head, where it is directed by a deflector into a predetermined
spray pattern. Sprinkler systems may suppress a fire, or inhibit
its growth, thereby saving lives and limiting inventory loss and
structural damage. Sprinkler specifications are published by the
National Fire Protection Association (e.g., NFPA 13, 13D, 13R).
[0004] The sprinkler system (more generally, Fire Protection
System, or FPS) is fed from a pump room or riser room. In a large
building the FPS consist of several "zones," each being fed from a
riser in the pump room. The riser contains the main isolation valve
and other monitoring equipment (e.g., flow switches, alarm sensors,
and the like). The riser is typically a 6 or 8 inch diameter pipe
coupled through a booster pump (called the fire pump) to the main
water supply to the building. The riser then progressively branches
off into smaller "cross mains" and branch lines, also known as
"zones". At the furthest point from the riser, typically at the end
of each zone, there is an "inspector's test port," which is used
for flow testing.
[0005] Many FPS are "wet" systems--meaning the sprinkler pipes in
each room are full of water under a predetermined "internal set
point" pressure. If the water pressure decreases below the set
point, valves are opened and/or a pump is activated, and water
flows into the sprinkler pipes in an attempt to maintain the
pressure. The set point pressure drops when water escapes the
system, such as due to the opening of a sprinkler head in a fire.
However, the system may also be activated by a broken sprinkler
head, or leaks in the system, such as leaks caused by corrosion of
the pipes.
[0006] Due to the possibility of water discharge in other than
actual fire conditions, a wet FPS present an unacceptable risk to
sensitive equipment or merchandise in many applications. For
example, a data center that houses expensive, mission-critical
computing or telecommunications equipment; a semiconductor
manufacturing facility; and a warehouse storing high-value,
non-waterproof merchandise, are examples of facilities in which a
wet FPS would be unacceptable. Also, areas subject to freezing
temperatures cannot utilize wet FPS.
[0007] To address the need for FPS in areas where a wet FPS is not
acceptable, alternatives to the wet FPS have been developed. These
are of two general categories. Dry FPS are typically used in areas
that are subject to freezing temperatures, where a water-filled
system is not practical (e.g., parking garages, non-heated attics
of motels and nursing homes, and the like). A dry FPS uses
compressed air in the piping as a "supervisory gas." The air is
maintained at a supervisory pressure, e.g., approximately 20 PSI.
When a sprinkler head opens, the air pressure drops to atmospheric
(e.g., 0 PSI), and a valve opens in response to the lower pressure.
The valve locks in the open position and water rushes into the
system. Dry FPS address the freezing problem, but present the same
hazards of loss or damage to expensive equipment or merchandise as
wet FPS, if the dry FPS is activated due to sprinkler head damage
or failure, or a leak such as from corroded pipes.
[0008] Pre-Action FPS, also called a double interlock dry FPS,
protects against water damage by increasing the probability that
the system is only activated by an actual fire. A pre-action FPS
operates similarly to a dry FPS; however, two or more action
signals are required before water is injected into the system. A
drop in supervisory air pressure alone will not activate the water
isolation valve unless a second signal, such as a heat or smoke
detector signal, is received by the control panel. At that point
the isolation valve will open and water will rush into the zones
with the aid of a booster pump called the fire pump.
[0009] Both dry and pre-action FPS must be hydro-tested after
initial installation to make sure that the piping and hangers can
support the additional weight of the water, and to make sure that
the flow rate of water through the system conforms to applicable
specifications (e.g., the NFPA 13 standard). Once it has passed all
the tests, the system is drained and then filled with compressed
air (supervisory gas). However, the FPS pipes never drain
completely, and the residual water that remains creates ideal
conditions for the initiation and propagation of corrosion in the
piping either by means of galvanic or organic induced corrosion.
Sometimes, microbes can grow in the water and accelerate the
corrosion by means of the byproducts that they produce during their
metabolic cycle. This is called Microbiologically Influenced
Corrosion (MIC). Over time, MIC or galvanic corrosion can cause
extensive damage to an FPS, as corrosion-induced leaks cause loss
of supervisory gas, either arming (pre-action FPS) or activating
(dry FPS) the system. Compressed air is used to maintain the
supervisory pressure in both Dry and Pre-Action FPS, and this
compressed air provides the oxygen that induces the galvanic
corrosion and/or MIC, when the FPS is laden with residual water
after draining from the hydrotesting.
[0010] Most real-world dry and pre-action FPS leak pressure. The
allowable leak rate 1 PSI per 24 hours, per NFPA specifications.
Conformance with this leak rate is tested following the
hydro-testing, and if it is in compliance, the FPS is certified.
From that point on, the supervisory gas leak rate only increases
over time, due to dried out pipe coupler gaskets, fitting compounds
(i.e., "pipe dope") drying out, and the like. In practice, most
building owners are not concerned about the increased in leak rate
until the air compressor providing the supervisory gas begins to
cycle excessively to maintain the supervisory pressure. Eventually,
it cannot maintain the required pressure, and the FPS will trigger
an alarm, requiring that the leaks be found and sealed, or that a
larger compressor be installed.
SUMMARY
[0011] According to one or more embodiments described and claimed
herein, an inert gas Fire Protection System (FPS) uses an inert gas
rather than air in a dry or pre-action type FPS. The inert gas
reduces or eliminates oxygen which in turn inhibits bacterial
growth, and hence mitigates Microbiologically Influenced Corrosion
(MIC) in the FPS piping. A zone purging valve having an inert gas
purity analyzer is disposed at the end of each zone in the FPS. A
controller over-pressurizes the FPS with inert gas, and bleeds the
gas through the zone purging valves to a predetermined supervisory
pressure. The zone purging valves can either be continuous,
automatic with self over-pressurization relief, or controlled from
the controller. The combination of the over-pressurization and
bleeding through the zone purging valves ensures inert gas at the
desired purity is maintained throughout the FPS. The purity of the
inert gas is periodically measured in bleed operations, and pure
inert gas is injected to maintain a predetermined purity level.
Prior to converting a conventional FPS to an inert gas FPS, a
pressure transducer and data logger measure the gas leak rate in
the FPS piping, to accurately size the required inert gas generator
or storage tank.
[0012] One embodiment relates to a method of inhibiting corrosion
in fire protection system piping. The fire protection system is
hydro-tested, and water is drained from the fire protection system
piping. Oxygen in the fire protection system piping is purged by
replacing it with an inert gas. The inert gas is maintained in the
fire protection system piping at a predetermined supervisory
pressure and at a predetermined purity level.
[0013] Another embodiment relates to a fire protection system. The
FPS includes piping operative to carry water over areas to be
protected from fire, and a plurality of sprinkler valves operative
to discharge water when a fire is detected. The FPS also includes
an inert gas control system in gas flow relationship with the
piping and operative to selectively inject inert gas from an inert
gas source into the piping, and further operative to monitor and
control the pressure of the inert gas in the piping. The FPS
further includes one or more analyzing vents in gas flow
relationship with the piping, disposed remotely from the inert gas
control system, and operative to selectively vent gas from the
piping and further operative to analyze the purity of the vented
gas.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a functional block diagram of an inert gas Fire
Protection System (FPS) according to one embodiment of the present
invention.
[0015] FIG. 2 is a flow diagram of a method of inhibiting corrosion
in FPS piping.
[0016] FIG. 3 is an elaboration of block 120 of FIG. 2.
[0017] FIG. 4 is an elaboration of block 150 of FIG. 2.
[0018] FIG. 5 is an elaboration of block 160 of FIG. 4.
[0019] FIGS. 6A and 6B are sectional views of a continuous leak
valve.
DETAILED DESCRIPTION
[0020] FIG. 1 depicts a non-wet, inert gas Fire Protection System
(FPS) 10, according to one embodiment of the present invention,
which inhibits Microbiologically Influenced Corrosion (MIC) and/or
galvanic corrosion and prevents or minimizes leaks to the system.
The inert gas FPS 10 may be configured and operated as either a dry
FPS or a pre-action FPS, as desired or required. The inert gas FPS
10 operates similarly to a conventional dry FPS or pre-action FPS,
with the exception that the supervisory gas is not compressed air,
but rather an inert gas that inhibits or retards galvanic corrosion
and/or bacterial growth, and hence MIC. In a presently preferred
embodiment, the inert gas is nitrogen (N.sub.2), due to the ease
and low cost of extracting high-purity nitrogen from ambient air.
However, any non-reactive gas, such as helium, neon, argon, or the
like, may be utilized within the scope of the present
invention.
[0021] Nitrogen is an inert gas, having no oxygen component. By
replacing the compressed air in a conventional dry or pre-action
FPS with nitrogen, galvanic corrosion and bacterial growth is
inhibited, which precludes the generation of metabolic byproducts
that cause MIC. Additionally, nitrogen has a dew point of
-40.degree. F. (far below that of compressed air), meaning it can
absorb water vapor at any higher temperature. By periodically
purging and renewing the nitrogen in the FPS pipes, residual water
from hydro-testing is evaporated and removed, virtually eliminating
future corrosion due to galvanic corrosion or MIC in the FPS
pipes.
[0022] Referring to FIG. 1, the distinguishing features of the
inert gas FPS 10 comprise a controller 12, which may include a
nitrogen generator 13, and one or more zone purging valves 14,
preferably located proximate to the end of each FPS zone 20 pipe on
or near an FPS Inspector's Test Port (not shown). Each zone purging
valve 14 can either be continuously vented, have a self-limiting
automatic vent with over-pressurization relief, or can be
controlled by the controller 12 via a wired or wireless connection.
In one embodiment, at least one zone purging valve 14 per zone 20
may include a gas purity analyzer 15, as described in greater
detail herein. The water distribution portion of the inert gas FPS
10 is conventional, comprising a riser 16 receiving water from a
reliable source, a fire pump or valve 18, and one or more zones 20
branching off from the riser 16. Sprinkler heads 22 are disposed at
regular intervals along the zone 20 piping.
[0023] The controller 12 controls the overall system 10 operation,
receiving input from one or more supervisory pressure sensors (not
shown), and in the case of a pre-action type system 10, also
receiving a secondary fire alarm, such as from a smoke detector or
heat sensor (not shown). The controller 12 preferably includes a
nitrogen generator 13 operative to extract nitrogen gas from
atmospheric air. A suitable nitrogen generator 13 is the
MICBIast.TM. FPS Nitrogen Generator, available from South-Tek
Systems of Wilmington, N.C. Reserve nitrogen may be generated and
stored in a tank 24. In one embodiment, for example in a small
building with only one or a few zones 20, the controller 12 may not
include the nitrogen generator 13, but may alternatively operate
using nitrogen (or other inert gas) supplied from a tank 24. In
either case, the controller 12 injects an inert gas into the riser
16 and/or zones 20, such as through an isolation valve 26,
downstream of the fire pump or valve 18. The inert gas is
maintained at a supervisory pressure and monitored, in conformance
with all NFPA (and other) specifications. If the controller 12
detects a drop in supervisory pressure--and additionally, in the
case of a pre-action type system 10, it receives a secondary fire
alarm--the controller 12 shuts off the inert gas isolation valve 26
and activates the fire pump or valve 18 to flood the zones 20 with
water.
[0024] An overall method 100 of inhibiting corrosion in fire
protection system piping is depicted in FIG. 2. The inert gas FPS
10 is hydro-tested according to all applicable standards, with all
concomitant testing and certification activities (block 102). Water
is drained from the FPS 10 piping (block 104), and oxygen is purged
from the FPS 10 piping by replacing it with an inert gas (block
120). This operation is further elaborated below, with reference to
FIG. 3. The inert gas is then maintained in the FPS 10 piping at a
predetermined supervisory pressure and at a predetermined purity
level (block 150). This operation (which may require reapplication
of block 110, as indicated by the dashed line) is further
elaborated below, with reference to FIG. 4.
[0025] FIG. 3 elaborates block 110 of the method 100 depicted in
FIG. 2. Oxygen is initially purged from the FPS piping by replacing
it with an inert gas (block 112). The inert gas is injected into
the FPS piping until the inert gas reaches a pressure (e.g., 30-40
PSI) in excess of the predetermined supervisory pressure (e.g.,
15-20 PSI) by a predetermined amount (block 114). The inert gas is
then bled (block 116) from one or more zone purging valves 14 (see
FIG. 1). At least one of the zone purging valves 14 includes a gas
purity analyzer 15 (e.g., nitrogen purity analyzer) operative to
measure (directly or indirectly) the purity of inert gas being bled
from the associated zone purging valve 14. In one embodiment, the
gas purity analyzer may comprise an oxygen sensor, which measures
the purity of inert gas by the reduction or elimination of oxygen.
The purity analyzer 15 reports the measured purity of inert gas,
via a wired or wireless connection, to the controller 12. If the
predetermined purity level of inert gas has not been achieved
(block 118), the FPS piping is again over-pressurized (block 114),
and bled (block 116). When the purity analyzer 15 reports that the
inert gas being bled at the zone 20 end has achieved the
predetermined purity level (block 118), the controller 12 closes
the zone purging valves 14 (block 120). Achieving a predetermined
purity level of inert gas (e.g., 99% pure nitrogen) ensures that
effectively no oxygen remains in the system to support bacterial
growth. Additionally, the bleed process of achieving the
predetermined inert gas purity removes water vapor from the FPS
piping, which has evaporated into the inert gas from residual pools
left from hydro-testing.
[0026] In one embodiment, the cycling of over-pressurization and
bleeding is accomplished with a zone purging valve 14 having a
predetermined constant purge level, wherein actuation of the
purging valve 14 by the controller 12 is not required. One suitable
such zone purging valve 14 is the AutoPurge System.TM. (APS) 30,
depicted in sectional views in FIGS. 6A-B, available from South-Tek
Systems of Wilmington, N.C. The APS 30 comprises a standard
threaded coupling 32 on an inlet, by which the APS 30 may be
mounted to the FPS piping, such as via an Inspectors Test Valve. A
retaining clip 34 retains a ball 36 within the inlet. In an
inactive state, as depicted in FIG. 6A, the ball 36 allows gas to
pass through a central passage 38 of the APS 30 and through a
calibrated orifice 40. The orifice 40 is preferably easily removed
(e.g., threaded) and may be sized, in terms of flow rate, for each
FPS system 10. For example, the orifice 40 in each APS 30 may be
sized to continuously purge gas such that the overall FPS system 10
loses pressure at a rate below the NFPA maximum leak rate of one
PSI per twenty-four hours. Gas passing through the calibrated
orifice 40 is discharged from the exit bore 42.
[0027] In one embodiment, the exit bore 42 is threaded, and accepts
an adaptor 44. The adaptor 44 may be sized to accept a gas purity
analyzer 15, such as the portable Quick-Check.TM. Nitrogen Purity
Sensor available from South-Tek Systems of Wilmington, N.C., or a
permanent gas purity analyzer 15, which may have a wired or
wireless connection to the controller 12. When water is pumped into
the FPS system 10, the APS 30 assumes an active state, depicted in
FIG. 6B, in which water pressure forces the ball 36 to seat against
an o-ring 46. This closes off the central passage 38, preventing
the water from leaking out of the APS 30.
[0028] FIG. 4 elaborates block 150 of the method 100 depicted in
FIG. 2. Once the predetermined purity level of inert gas has been
achieved, the inert gas is maintained in the FPS piping at a
predetermined supervisory pressure and at the predetermined purity
level, even in the face of minor leaks in the FPS fittings,
couplings, and the like. The maintenance operation 150 begins with
the inert gas FPS 10 piping filled with inert gas of a
predetermined purity level at a predetermined supervisory pressure
(step 152). If the controller 12 detects an inert gas pressure
below the predetermined supervisory pressure (block 154), an alarm
is triggered (block 160), and a signal may additionally be
communicated by the controller 12 to, e.g., a Building Management
System (BMS). Block 160 is further elaborated below, with reference
to FIG. 5. If the inert gas pressure is maintained at the
predetermined supervisory pressure (block 154), i.e., there are no
leaks in the FPS 10, the controller 12 periodically (e.g., every
few days) bleeds a sufficient volume of gas through at least one
zone purging valve 14 having a gas purity analyzer 15, to measure
the purity of the inert gas (block 180). If the measured purity of
the inert gas is below the predetermined purity level (block 182),
pure inert gas is injected into the system, following the method
described above, beginning with block 114 of FIG. 3.
[0029] In practice, there are different levels of inert gas leaks,
raising different levels of concern. In one embodiment, a plurality
of distinct alarms is generated and reported, based on the severity
of the detected leak. FIG. 5 depicts a method 160 of quantifying
detected leaks, and reporting different alarms based on the
severity of the leaks. To quantify the leak severity, the inert gas
in the FPS 10 is brought up to the predetermined supervisory
pressure and a timer is initialized and started (block 162). The
controller 12 monitors the pressure in the FPS 10. When a pressure
below the supervisory pressure is detected (block 164), the
controller 12 injects inert gas into the FPS 10 piping, and reads
the timer when the predetermined supervisory pressure is again
achieved.
[0030] Based on the value of the timer (i.e., the time required to
reach the predetermined supervisory pressure at a known flow rate
of fresh inert gas), one of several levels of alarm is generated.
In one embodiment, if the controller 12 injects inert gas for less
than x hours per day to maintain the predetermined supervisory
pressure, a level 1 alarm is reported, e.g., to the BMS. A level 1
alarm indicates a slow leak, which may not be of concern. If the
controller 12 must inject inert gas for more than x hours per day,
but less than y hours/day, a level 2 alarm is generated and
reported. A level 2 alarm indicates a significant leak above the
acceptable level, but which does not adversely impact the
functionality of the inert gas FPS 10. A leak causing a level 2
alarm should be addressed soon. If the controller 12 must inject
inert gas for more than y hours per day--up to an including
continuous operation--a level 3 alarm is generated. A level 3 alarm
indicates a catastrophic leak that may affect the ability of the
inert gas FPS 10 to function properly. A level 3 alarm must be
addressed immediately.
[0031] The values for the variables x and y may be readily
determined by those of skill in the art for each installed system,
and will generally vary based on the total volume of FPS 10 piping,
the inert gas injection flow rate, and will include a subjective
factor as to where to draw the lines between acceptable,
significant, and catastrophic leaks. Also, the units for x and y
described above--hours per day--assume a controller 12 with a
nitrogen generator 13 and no reserve storage tank 24, and indicate
the time that the nitrogen generator 13 must run. When the inert
gas is supplied from a tank 24 of compressed gas, the duration
variables x and y may refer to the time the isolation valve 26 is
open, and may be, e.g., minutes per day, minutes per hour, or other
appropriate unit.
[0032] Of course, while the embodiment described above and in FIG.
5 uses two threshold variables x and y, and reports three levels of
leak severity alarm, other embodiments may use any number of
threshold variables, and may report any number of levels of leak
severity alarm, as desired or required for any particular
installation. In general, the controller 12 may be easily
programmed to generate and report the desired leak alarms. Also,
the use of a timer in the description of the alarm method 160 is
only to describe functionality--in practice, the duration of inert
gas injection may be measured in numerous ways. Furthermore, the
total volume of gas injected may be measured in lieu of the
duration of injection at a known flow rate, and appropriate alarm
levels may be set accordingly. All such variations fall within the
scope of the present invention.
[0033] The inert gas FPS 10 of the present invention may be
implemented on existing dry or pre-action FPS systems. As mentioned
above, most such systems leak air. Building owners are generally
not concerned about such leaks, until the air compressor providing
the supervisory gas begins to cycle excessively to maintain the
supervisory pressure. However, when the air compressor is replaced
with an inert gas source 13, 24 and the controller 12, gas leaks in
the FPS piping become much more costly (so long as the inert gas is
more expensive to replace than air, which is generally the
case).
[0034] In one embodiment, the gas leak rate of an existing dry or
pre-action FPS is determined, in order to determine the appropriate
size nitrogen generator 13. The existing FPS has a supervisory
pressure air compressor, with an accumulator tank, plumbed into the
FPS piping. The air compressor pressurizes the FPS piping to a
predetermined supervisory pressure. As air leaks from the FPS
piping, the pressure decreases. When the FPS piping pressure drops
to a predetermined trigger pressure, the air compressor
automatically starts up, and re-pressurizes the FPS to the
predetermined supervisory pressure.
[0035] To measure the gas leak rate, a pressure transducer is
installed in the FPS piping, or may be connected to a supervisory
pressure air compressor accumulator tank. The pressure transducer
is connected to a data logger, which records the pressure in the
FPS piping. As the air compressor runs the FPS piping pressure (and
that in the air compressor accumulator tank) to the required
supervisory pressure and shuts off, and as the pressure within the
FPS piping (and that in the air compressor accumulator tank)
decreases due to leaks, the pressure variations vs. time are
recorded. By knowing the output of the air compressor (e.g., in
cubic feet per minute, or CFM), the FPS piping leak rate (also in
CFM) can be easily calculated. Based on this existing leak rate,
the size of a nitrogen generator 13 (or inert gas storage tank 24)
required to provide sufficient flow to overcome the leak rate and
maintain the required supervisory pressure with inert gas may be
calculated.
[0036] In one embodiment, the pressure transducer may be attached
to an existing FPS at a test port that includes a ball valve. The
pressure transducer is screwed into the pipe fitting right after
the existing ball valve, and the ball valve is then opened to allow
the transducer to sense the FPS piping pressure. The pressure
transducer may attach via a wired connection to a portable, battery
operated data logger. Alternatively, the pressure transducer may
connect via a wired or wireless link to a 110V data logger that is
plugged into a convenient outlet. The FPS is automatically
monitored for, e.g., 4 to 7 days, during which time the air
compressor may cycle numerous times. Based on the data accumulated
during this period, the FPS leak rate may be determined, given the
flow rate of the air compressor. Knowledge of the existing FPS leak
rate is important in selecting an inert gas source 13, 24. If, for
example, a nitrogen generator 13 is selected that is too small, it
will be unable to achieve or maintain the predetermined supervisory
pressure. On the other hand, if too large a nitrogen generator 13
is selected, the building owner pays a higher cost than is
required.
[0037] In one embodiment, as described above, the controller 12 is
a stand-alone unit operative to control the inert gas FPS 10. For
example, the controller 12 may comprise a computerized unit based
on a general purpose microprocessor, Digital Signal Processor
(DSP), or the like, programmed with software operative to implement
the described control functions. Alternatively, the controller 12
may comprise a custom control unit based on a state machine,
programmable logic and associated firmware, or the like. The
controller 12 as a stand-alone unit may include a user interface
such as a terminal having a keyboard and display, or inputs in the
form of switches and/or a keypad, and outputs in the form of
lights, audible alerts, and the like. In one embodiment, the
controller 12 may be integrated with a building's BMS or fire alarm
panel. As such, the controller 12 may perform continuous monitoring
of inert gas pressure and purity, as described above. In all
embodiments, the controller 12 receives input from various sensors
(pressure sensors in each zone 20, smoke detectors, the purity
analyzers 15, and the like) and outputs control signals (to the
zone purging valves 14, the fire pump or valve 18, the isolation
valve 26, any inert gas storage tank 24, and the like) as well as
alarm outputs and system information output to a BMS or fire panel.
Any or all of these control and communication links may be wired or
wireless, using any known or newly developed protocols (e.g.,
RS-232, IEEE-488, IEEE-1394, USB, Ethernet, IEEE 802.11, Bluetooth,
or the like).
[0038] The present invention may, of course, be carried out in
other ways than those specifically set forth herein without
departing from essential characteristics of the invention. The
present embodiments are to be considered in all respects as
illustrative and not restrictive, and all changes coming within the
meaning and equivalency range of the appended claims are intended
to be embraced therein.
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