Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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METHOD OF CLEANING A POTABLE WATER
DISTRIBUTION PIPING SYSTEM
TECHNICAL FIELD
toooll The present invention relates to a non-
structural pipe rehabilitation method for cleaning a potable
or non-potable water distribution piping system and which
relies on a synergetic combination of thermo, hydro-
pneumatic and chemical processes to remove accumulated
deposits on the inner wall of sections of such pipes.
BACKGROUND ART
tooo2l Municipalities and industries are faced with a
tremendous challenge to rehabilitate the underground water
infrastructure. Specialists in the field and most municipal
engineers will confirm that the service life of more than
50°s of the buried water infrastructure has reached the end
of their service lives. According to the USEPA, the needs
are numbered at $77 Billion dollars to maintain or replace
the underground water distribution pipes in the next 20
years. In several cities or town, this problem covers 40% to
60% of the networks . In summary, thousands of miles of pipe
are in need of repair at this time.
tooo3l Considering the enormous cost to meet this
challenge, public and private corporations are looking at
different alternatives to restore the pipes up to their
original standards. The most common problem is the scale
deposition and sedimentation inside the pipe, reducing the
pipe hydraulic carrying capacity. Among all available
rehabilitation methods available on the market today,
trenchless rehabilitation technologies seem to be the most
interesting since they are safe, cost-effective and most
important, cause little or no inconvenience to the public
and to the environment.
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Iooo4) The accumulation of sediment on the pipe inner
walls has tremendous negative consequences to the general
public. Inconveniences include the restriction of flow for
fire protection, higher energy cost to pump the water in the
system due to the restrictions in the pipe, poor water
quality to the customers because of the reddish colour
occurring in events of increased water demands such as pipe
flushing, or any other use of water from the hydrants for
street cleaning, watering, etc.
Iooo5) One of the main concerns is for fire protection.
New government regulations provide Fire Protection
guidelines that any public water distribution system
provides a predetermined volume of water at a hydrant as per
its geographical location and type of protection coverage,
i.e., residential, industrial, or commercial.
Iooos) When water pipes get severely encrusted over time,
the fire hydrants do not provide access to the flows for
which the distribution system was originally designed. This
problem forces fire protection personnel to modify their
fire fighting strategies, which are then often compromised
and diminished. In addition, the urban development plan is
also compromised, disfavouring low flow areas.
fooo~) When the accumulation of sediment is the problem,
non-structural rehabilitation methods are often the solution
of choice. However, one must confirm the residual
structural condition of the inner pipe wall before
determining the best rehabilitation method to choose. All
non-structural rehabilitation methods have benefits, but
vary in performance, safety and costs.
Iooos) Non-structural rehabilitation methods include the
use of powerful toxic acid circulating inside the pipe to
soften and dislodge the sediments. Such are disclosed in
U.S. Patent No. 5,885,364, No. 5,360,488 5, No. 5,680,877
and No 5, 800, 629. Counting only on the recurring effect of
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the acid to dislodge the hardened deposits on the pipe wall,
the soaking time period is very long.
tooos) One of the disadvantages of that technique is the
general public conception and reluctance to the use of the
toxic acid in potable water systems. Other areas of concern
include the risk to the environment, infiltration of the
toxic acid in other parts of the system because of non-tight
main valves or service connection lines, danger to the
manpower that must execute the fieldwork and manipulate the
acid, and the prolonged interruption of potable water
service to customers.
toooio) Because of the toxic property of the acid, leaks
are often caused on the pipe during the course of the work.
The situation then becomes very dangerous and a health risk
for those that must come in contact with the product to
clean the pipe and fix the leak. In several cases, the
government authority must be made aware immediately when a
pre-determined volume of toxic acid has been freed in the
environment. In addition, the strong penetrating property
of the acid will tend to dislodge the deposits so much that
it will clean the pipe wall all the way to its bare
material, exposing the pipe wall, creating red water
occurrences in the system and upsetting the general public.
toooii) It must be noted that the acid technique can only
be used for water distribution systems using inhibitor
products such as poly-phosphate or ortho-phosphate, as a way
to capture iron particles and preventing the colouring of
the water. The treatment with the inhibitor products is
necessary as an integral part of the water treatment when
choosing the toxic acid method as a way to clean the water
pipe. This treatment is obviously an additional expense for
both the product itself, and the constant monitoring. For
the reasons mentioned above, most private and public water
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distribution system managers are not opting for the toxic
acid cleaning method.
foool2~ Another method is the use of compressed air and
water. This method is called "Air Scouring", see U.S.
Patent No. 5,915,395, such method having been developed in
the U.K. The method provides a cleaning of the water main
in one direction, from one fire hydrant to the next.
However, this method is used mostly for the cleaning of the
water main rather than for the rehabilitation, as it doesn't
allow the removal of tubercles and other hardened deposits
on the inner pipe wall. Air Scouring is a cleaning method
often used for pipe having a Hazen-Williams coefficient
(HWC) of above 80. The Hazen-Williams coefficient is the
major loss calculation for water in pipes using a friction
loss equation. For example, a new iron pipe has a HWC of
130. A 40-year-old pipe has a HWC ranging from 64 to 83.
The HWC gradually diminishes as the pipe gets older.
Iooo137 In summary, Air Scouring is the injection of
compressed and treated air inside the water main through a
fire-hydrant. Along with-the air, water is introduced in
the pipe by using what is called a control valve, located
downstream for the hydrant which is an existent valve only
partly opened. The air, along with the water, create what
is called slugs. Moving at very high velocities of above 10
fts in the main, the slugs contribute to removing the non
solidified deposits. Air Scouring also include the
injection of a poly-phosphate product to contribute to the
cleaning. Reaction time of the poly-phosphate is very short
and do not contribute to the removal of the hardened
deposits.
SUMMARY OF INVENTION
tooo147 It is a feature of the present invention to
provide a method of cleaning a potable or non-potable water
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distribution piping system which is safe, cost-effective and
environmentally friendly and which is capable of restoring
the hydraulic carrying capacity and/or the delivery of
quality water.
fooo151 Another feature of the present invention is to
provide a method of cleaning a potable water distribution
piping system and wherein a sediment dislodging product is
injected with air under pressure into the conduit whereby to
blast the deposited sediments incrusted on the inner wall of
the section of pipe being cleaned.
Iooolsl According to the above features, from a broad
aspect, the present invention provides a method of cleaning
a potable water distribution piping system. The method
comprises the steps of identifying a section of pipe to be
cleaned of deposited sediments incrusted on an inner wall
thereof. Two fire hydrants connected to the section of pipe
to be cleaned are also identified to define a flow path
through the section of pipe to be cleaned. All valves
connected to the section of pipe in the vicinity of the two
fire hydrants are also identified and closed to isolate the
section of pipe. An air compressor is connected to a nozzle
of one of the two fire hydrants upstream of a cleaning water
flow to be generated. A reservoir containing a sediment
dislodging product is connected to a second hydrant nozzle
of the fire hydrant having the air compressor connected
thereto. One of the valves connected in the vicinity of the
one fire hydrant upstream of a connection thereof with the
section of pipe to be cleaned is opened whereby to create a
minimal water flow therefrom into the section of pipe to be
cleaned upstream of the cleaning water flow to be generated.
A hydrant nozzle of the other of the two fire hydrants is
opened downstream of the cleaning water flow to be
generated. The compressor is then operated to inject air
under pressure inside the section of pipe to be cleaned
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through the fire hydrant and simultaneously the sediment
dislodging product is injected into the section of pipe to
be cleaned through that fire hydrant together with the air
under pressure. This creates spinning water pockets inside
the section of pipe to be cleaned and the sediment
dislodging product mixes with the minimal water flow
admitted through the opened valve whereby to blast the
deposited sediments from the section of pipe to be cleaned.
The cleaning water flow containing dislodged sediments is
flushed through the other fire hydrant by an open nozzle
thereof .
fooomy In association with the present invention, the
following services are rendered:
1. Consultation with the client to identify the faulty
pipe sections and determine the level of improvement
needed.
2. Through monitoring, sampling and/or laboratory
analysis, determine the exact nature of the problem.
3. Review test results and, aligned with client needs,
implement all, or a combination of the following steps:
3.1. Inspect, manipulate and assess the fire hydrants,
main valves and users' service lines related to
the project area.
3.2. Perform leak detection and isolation tests on the
pipe sections to be rehabilitated.
3.3. Clean users' service lines.
3.4. Pre-clean the pipe by using air, water and the
chemical pre-cleaning solution.
3.5. Soften the deposits by using hot water, and/or a
chemical cleaning solution.
3.6. Finalize the pipe cleaning by evacuating the
softened and dislodged material.
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4. Through monitoring, sampling and/or laboratory
analysis, confirm the effectiveness of the
rehabilitation.
BRIEF DESCRIPTION OF DRAWINGS
toooi8l A preferred embodiment of the present invention
will now be described with reference to the accompanying
drawings in which:
toooZS1 FIG. 1 is a block schematic diagram illustrating
the method of cleaning a potable water distribution piping
system in accordance with the present invention;
fooo2ol FIGS. 2 and 3 are schematic diagrams showing the
process of blasting the incrusted sediments from the inner
wall of a section of pipe being cleaned and using the method
in accordance with the present invention;
toooxy FIG. 4 is a block schematic diagram showing a
modification of the method as illustrated in Figure 1; and
tooo22~ FIG. 5 is a block schematic diagram illustrating
the method of cleaning the user lines associated with a main
water conduit.
DESCRIPTION OF PREFERRED EMBODIMENTS
tooo231 The following procedure is undertaken to identify
the faulty pipe sections and determine the level of
improvement needed to a potable water distribution piping
system. First, an evaluation and an assessment of the water
distribution system are done to identify the pipe sections
needing a non-structural rehabilitation. The evaluation
includes the identification of pipes that have an
appropriate metal thickness for a non-structural
rehabilitation. The evaluation also consists in
investigating the historic of leaks and breakages; the pipe
material, diameter and age; the identification of sections
that contribute to water quality complaints; the sections
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that do not provide sufficient pressures and flows, the
sections of the distribution system targeted for expansion;
the sections that are part of a rehabilitation master plan;
and the sections that show vulnerability in meeting water
quality government regulations and insurance requirements
pertaining to fire protection.
fooo24~ Samples are taken from the pipe sections to be
cleaned for laboratory analysis. The pipe sections water
samples may be kept, immediately after its collection in the
field, and at all times, in a container filled with water to
provide a similar condition as its day-to-day environment.
A chemical analysis of the deposits found in the pipe water
samples is performed to analyze the incrusted sediments, the
residual wall thickness, and the expected remaining service
life.
Iooo2sl In the field, the C-Factor (roughness coefficient)
of the pipe to be rehabilitated is measured using the Hazen-
William coefficient as recommended by the American Water
Works Association. The Hazen-Williams coefficient is the
major loss calculation for the water in pipe using a
friction loss equation. Another method for evaluating the
pipe C-Factor is to analyze the pipes' characteristics based
on the hydraulic model database.
Iooo2sl We also measure static and dynamic (residual)
pressures and flow at each fire hydrant located in the
project area to evaluate the true hydraulic performance of
the distribution system.
toooa~~ Based on the results of the laboratory analysis,
we determine the preferred water temperature, optimal
chemical solution and soaking time period necessary to
dissolve, dislodge and evacuate the deposits on the pipe
inner wall to restore the pipe hydraulic carrying capacity
during the cleaning and rehabilitation procedures. The
analysis procedures may include the soaking of the pipe in
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the chosen solution and periodically observe the
dissolution, softening and dislodging of the incrusted
sediments. The observations are made at regular intervals
at temperatures up to 180 degrees Fahrenheit for the
duration of the soaking.
fooo2el Referring to Figure 1, there is shown the
equipment used with the method of the present invention.
Before the start of the rehabilitation method, we inspect
and perform water tightness test on the fire hydrants 15,
18, 25, 27, and 31 and the water main valves 14, 16, 17, 19,
26, 28, 29, and 32 that will be used to carry out the
method. In addition, we inspect and manipulate all users'
service lines 20 connected to the section of pipe 21 to be
rehabilitated to confirm their proper operation. The
defective fire hydrants, main valves and service lines must
be repaired or replaced prior to the beginning of the
rehabilitation work.
(00029) In addition to the above, we perform a leak
detection test on the pipe section to be rehabilitated 21
and on the users' service lines 20 using an acoustic
correlator. We also perform an isolation test on the pipe
section to be rehabilitated by closing valves 17, 26, 28,
and 29. To confirm the proper isolation of the pipe, we
open fire hydrant 25. There should be no flow at the
hydrant. If there is a flow, find and repair the defective
valve(s).
fooo3o~ Cleaning of the pipe section 21 as shown in Figure
1 is a method or process using a combination of purified
air, water, blasting material such as ice pellets, floatable
plastic pellets, and/or any other material creating an
abrasive effect, and/or a non-toxic chemical solution. The
objective of the pre-cleaning is to remove the non-
solidified deposits and other loose residues and sediments.
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Iooo317 The method comprises closing the main valves 17,
26, 28 and 29 to isolate the pipe section to be
rehabilitated 21. If necessary, the users' service lines 20
connected to the pipe sections to be rehabilitated are
closed. In parallel to the valve closing operation, the air
compressor 1 is connected to the fire hydrant 25 using a
specially conceived hose 2 and adaptor. In addition, we
hook up, to the other fire hydrant nozzle 25, a hose
connected to a chemical container 22 and feed pump 23,
and/or we connect the hose to a pellet container 24. This
set up, based on the results of the sample laboratory tests,
is used to inject the pellets and/or a non-toxic blend of
surfactant and sequestering agent inside the water main.
tooo32~ The surfactant is used to penetrate the deposits
50 incrusted on the pipe wall 51, and contributes to
dislodging and transporting the deposits and other residues
to the exit fire hydrant 18, see Figures 2 and 3. In
addition, the surfactant will promote back pressure useful
to the generation of turbulences 53 and high sheer water
velocities necessary to properly dislodge the scaling and
hardened deposits 50. The sequestering agent softens the
hard deposits and therefore helps to improve the
effectiveness of the cleaning.
fooo331 Following the closing of the water main valves 17,
26, 28, and 29, fire hydrant 25 is opened. The pipe section
21 should still be filled with water. However, there should
be no water flow coming out of fire hydrant 25. If not, all
water main valves that were closed should be verified. It is
preferable to proceed with repair if a valve is found not to
be watertight.
(00034 Either valve 26, 28 or 29 are opened (valve 28 as
shown in Figures 2 and 3) to create a minimal flow 55
between ten (10) gpm to fifty (50) gpm at fire hydrant 25.
Then, hydrant 18 is opened, and the air compressor 1 is
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turned on to inject the air under pressure inside the water
pipe through the fire hydrant 25. The cubic feet per minute
(CFM) is adjusted considering the pipe diameter and Hazen-
Williams coefficient. Simultaneously, the chemical feed
pump 23 is turned on to inject the chemical solution 22
inside the water pipe 21 through the fire hydrant 25.
fooo351 The water, mixed with the chemical solution, is
then propelled inside the pipe by the compressed purified
air, creating the compacted pockets 53 intermittently
scrubbing on the pipe walls. Air purification is achieved
by successive steps of cooling and filtering, as shown at 57
in Figure l, through multi-levels cartridge filters (not
shown) in order to avoid oily contamination of the
distribution system. Effective pre-cleaning is achieved
when the adequate concentration of surfactant is added to
the water. The chemical solution is fed in concentrations
capable of generating the foam required to create the
adequate back pressure. Optimum efficacy occurs when foam
is produced.
foooss~ Pellets can also be used to dislodge the deposits
if it is deemed necessary during the laboratory tests.
Pellets contained in the container 24 are introduced in the
pipe through fire hydrant 25.
tooos7~ When foam reaches hydrant 18, the process is
stopped to let the pipe section to soak for a time period
determined during the sample laboratory test. The solution
will then penetrate and soften the deposits 50. Following
this soaking, the cleaning process is restarted for a period
of time anywhere between five (5) to thirty (30) minutes
based on laboratory tests results. Then, turn off the
chemical feed pump 23.
(ooo3sl The pellets and/or the chemical solution are
flushed away when there are no more pellets or foam showing
at hydrant 18. The turbidity is measured periodically and
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we continue on with flushing until turbidity readings are
back to near normal. Turbidity readings cannot be taken
when foam and/or pellets are present in the water. Deposits
removed from the surfaces contribute to the cleaning process
as they become themselves abrasive material when mixed with
the abrading pockets to blast away further deposits as they
travel down the pipe. Velocities linked to the spinning of
water pockets improve the blasting efficacy.
fooo3sl To complete the cleaning of pipe section 21, we
use the same cleaning procedures in the opposite direction.
For example, hydrant 18 becomes the feed hydrant, and
hydrant 25 becomes the exit hydrant. Reversing the
procedure will ensure a uniform cleaning of the entire pipe
length. Not surprisingly, pre-cleaning performance is
better in the late section of the pipe. This is why the
process is reversed to ensure a proper pre-cleaning of the
entire pipe length.
fooo4o~ Adding pellets will enhance the removal of
sediments and therefore contribute to reducing the soaking
time needed for the rehabilitation. The cleaning operation
is stopped when the turbidity readings are back to near
normal.
fooo4i~ When applicable, water flushing is performed along
the untreated pipe sections to flush out all the loose
material that were not evacuated during the pre-cleaning.
For this example, the untreated pipe sections to be flushed
are located between the water main valves 26, 28 and 29, and
fire hydrant 25.
(00042 With reference now to Figure 4, there is shown the
softening procedure which relies on the soaking with hot
water, and/or a strong, non-toxic food grade cleaning
solution to soften and break the first and hard layer of the
incrusted deposits 50 found on the pipe inner wall. The
other sediments, underneath the hard layer, are softer and
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easily removable during the hydro-mechanical cleaning phase
of the procedures. The softening procedures are very
similar to those described above. The major differences are
that the cleaning chemical solution may be replaced with hot
water, and/or with a strong, acidic chemical compound more
capable of performing extensive removal of hard deposits.
This compound, added to the water, forms a very strong
cleaning solution. The strong chemical cleaning solution
may or may not be heated depending on the laboratory test
results. Also based on laboratory test results, the soaking
time of the strong chemical solution is determined to
dislodge persistent deposits.
Iooo431 In addition to the equipment mentioned above,
boiler 37 and associated apparatus 35, 36 and 37, is needed
to allow the heating of the water and/or the strong cleaning
solution. The main purpose for injecting heated liquids
into a pipe is to heat the pipe material and therefore
engender its expansion to splinter the sediments and provide
easier access and penetration of the cleaning solution in
the core of the sediments 50. As an example, the extension
of a cast iron pipe is of .07 inch at every 100 feet of pipe
for every l0 degrees Fahrenheit increase in pipe
temperature.
fooo441 A fire hydrant 27 is selected that is not
connected to the pipe section 21 to be cleaned. This fire
hydrant will be used to supply the potable water necessary
to feed the boiler device 37 used to heat the water. The
device 37 must convey the hot liquid into a storage tank 36
using a specially conceived hose.
fooo451 As per the results of the sample laboratory tests,
the water and/or the cleaning chemical solution is heated to
a predetermined temperature. The hot liquid is then
transferred into a watertight reservoir 36 specially
conceived to store hot liquids . Once the appropriate volume
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of hot liquid has been poured in the storage tank, pump 35
feeds the hot liquid into the pipe section 21 through fire
hydrant 25. The hot liquid slowly fills the pipe sections
to be rehabilitated and will eventually come out of fire
hydrant 18 as the pipe is entirely filled. We keep flushing
the hot liquid at fire hydrant 18, and we monitor
temperature, and close the gate valve at the hose nozzle 18'
of fire hydrant 18 when the proper temperature has been
reached, as determined during the laboratory tests.
X000461 If a chemical solution is used for soaking instead
of hot water, the spent solution will be transferred into a
tank 40 and neutralized with an alkaline material in order
to safely be disposed of in the sewer system. A very small
portion of liquid from the pipe section is emptied to allow
a stop-and-go movement of the hot liquid. Air is injected
intermittently using the compressor at fire hydrant 25 to
intensify the movement of the hot liquid in the pipe. This
will harmonize the liquid temperature on the entire pipe
length. The hot liquid is left to soak in the pipe for a
time period as determined during the laboratory tests.
fooo4~~ Following the soaking, the procedure as described
above is repeated to clean the pipe and the hot water and/or
strong cleaning chemical solution are evacuated along with
the dissolved materials. If a chemical solution is used for
soaking instead of hot water, the spent solution will be
transferred into a tank 40 and neutralized with an alkaline
material in order to safely be disposed of in the sewer
system.
fooo4a~ Following the rehabilitation and all the steps as
described above, the pipe section is disinfected using the
ANSI/AWWA C651-99 standards by the American Water Works
Association (AWWA).
fooo4s) Following the cleaning of the pipe section 21 and
to ensure that the rehabilitation objectives have been met,
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the following field tests and measurements are performed:
the Hazen-Williams coefficient measurement; the leak
detection using acoustic correlator; the static and dynamic
pressures on the fire hydrants 18 and 25 that are included
in the method are measured and also on those surrounding the
project area, and the standard water quality tests including
turbidity and residual chlorine are performed. The purpose
of those tests is to review the hydraulic and water quality
results following the pipe rehabilitation, and to confirm
the level of improvement and effectiveness of the method.
fooo5ol Referring to Figure 5, there will now be described
the method of cleaning the user's service lines 20 to
provide full benefits related to the rehabilitation of the
water main. For the service line 20, outfitted with a water
meter 11, the valve 5 must be closed upstream from the meter
before disconnecting the service line. The line is cut and
with a hose 2, the air compressor 1 is connected thereto
with a connector suitable for the type and the size of the
service line 20. The hose must be equipped with a ball
valve. Then, the service line valve 5 must be re-opened.
Iooosi~ For the service line not outfitted with a meter,
the valve 3, located inside the building 12, must first be
closed. The service line 20 must be disconnected downstream
of the valve 3. The service line 20 is cut and with a hose
2 it is connected to the air compressor 1 with a connector
suitable for the type and the size of the service line 20.
The hose must be equipped with a ball valve. During the
installation, the exterior valve 5 remains opened.
fooos2~ When the installation of the equipment is
completed, the water main valve 10, located downstream of
the fire hydrant 8, must be closed to prevent the spreading
of the sediments throughout the entire distribution system.
It is preferable to flush the sediments in the same course
as the normal direction of flow 6 in the main pipe section
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7. The procedure is not necessary if the water main is a
dead end. When the valve 10 is closed, fire hydrant 8 must
be fully opened. Following the opening of the fire hydrant
8, the air compressor 1 must be turned on to push the
sediments down the line and the water main pipe. The
compressor must deliver the proper cubic feet per minute
(CFM) air pressure to ensure the removal and evacuation of
all sediments incrusted inside the service line 4.
Iooos3l During the cleaning of the service line, the
flushed water 9 from the hydrant 8 should be colored and the
turbidity very high. It is important to flush the hydrant 8
until the water reaches a turbidity level of 10
Neophelometric Turbidity Unit (NTU) or less. As above-
mentioned, this is a measurement of the cloudiness of water
due to suspended particles in the water (clay, silt, rust,
etc). Lower is the reading, clearer is the water. When the
turbidity level is at 10 NTU or less, the air compressor 1
can be turned off. The main water valve 10 is reopened and
the air compressor 1 is disconnected from the service line
20 and the water meter 11 is reconnected. The re-connection
of the service line to the water main is performed to
standards. Open and flush a water tap inside the building
for at least five (5) minutes and proceed with water quality
tests to ensure the safe use of the water.
fooos4~ It is within the ambit of the present invention
to cover any obvious modifications of the preferred
embodiment described herein provided such modifications fall
within the scope of the appended claims.
