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Air & Water Tests
All lengths of sewer drain up to DN 750 should be tested
for leakage by means of air or water tests.
These tests should be applied after laying and before
backfilling. Some backfill may be placed at the centre of
each pipe to prevent movement during testing.
We strongly recommend that air testing be
undertaken periodically during the laying process,
say every fourth pipe, so as to facilitate
rectification if any defect is found.
Short branch
drains connected to a main sewer between manholes
should be tested as one system with the mains sewer.
Long branches should be seperately tested.
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Man entry sizes of pipeline can be physically inspected
while smaller diameters can be visually inspected from
manholes of by means of T.V. camera’s.
Visual inspection: Check for-
- obstructions and debris,
- structural soundness of pipes,
- joints properly sealed,
- line and level within tolerance.
Water Test
A water test is the more logical and conclusive method
of testing a completed pipeline but problems of
availability and disposal of the quantity of water involved
may cause difficulty. Before backfilling, leakage can be
clearly located, its amount assessed and where
necessary appropriate remedies applied.
Click here to view larger diagram
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To test the pipeline:-
- Insert plugs in both ends of the drain or sewer and in
connections if necessary. Precautions should be
taken by strutting or otherwise to prevent movement
of the drain or sewer during testing.
- Fill the system with water ensuring all the air has
been expelled.
- Allow at least two hours before test readings are
taken to allow conditions to stabilise, adding water to
maintain the test head.
It may be necessary to extend this period for large
diameter pipes, up to twenty-four hours or more
before a stable condition is reached.
- Apply required test head at the upper end by means
of a flexible pipe leading from a graduated container or stand pipe.
- Apply the test pressure of 1.2m head of water above
the soffit of the drain or sewer at the high end with a
maximum of 6m head at the low end. If it exceeds 6m test the drain or sewer in stages.
- Measure the loss of water over a period of 30
minutes by adding and metering quantities of water
at intervals of 5 minutes to maintain original water
level in the standpipe.
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Over this 30 minute period the quantity of water added
should not exceed 0.05 litre per 100 linear meters per
millimetre of nominal size of the drain or sewer, i.e. for
a 150m length of DN 800 for the allowable leakage
would be:
0.05 x 150/100 x 800 = 60 litres
Should the pipeline not comply with these
requirements it will probably be attributable to
one of the following:-
- leakage from test equipment
- trapped air,
- leakage from joints, e.g., displaced ring,
- leakage from damaged or defective pipe.
Click here to view larger diagram
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AIR & WATER TESTS
Air Test
The air test is very searching and is more convenient
than the water test, but the leakage rate cannot be
measured accurately. An excessive drop in pressure in
the air test may indicate a fault in line such as a
displaced sealing ring. It may be due to faults in the
testing apparatus. Therefore the first check must be on
the apparatus, especially the seals of the stop ends and
all connections. The point of any leakage may be difficult
to detect but spraying with soap solution could indicate
such leakage by the presence of bubbles.
Failure to pass this test in not conclusive and, when
marginal failure does occur, a water test as described
should be made and the leakage rate determined before
a decision as to rejection is made.
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Air test requirements are currently specified in British
Standard Codes of Practice BS 8301 'Building Drainage'
and BS 8005 'Sewerage'.
(5 minute test 100mm on U
tube to drop no more than 25mm).
However current
practive in many other European Countries confirms the
research by CPA that the introduction of a higher
pressure test to 1000mm rather than the current 100mm
would overcome most of the shortcomings in BS test.
These may be summarised as follows:-
- The BS air test specifies a constant requirement
regardless of diameter and length of the pipeline.
- The air test is relatively more sever on smaller pipe
diameters.
- Pipe wall dampness affects air test results,
particularly on smaller diameter pipes and at the low
pressure specified.
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To test the pipeline, fit strutted plugs at each end and
pump air until a pressure of 1m head is shown on the U
tube. Allow the pressure to drop recording the time for
the head to fall from 900mm to 800mm. This time should
not be less than that shown in the table above for the
appropriate nominal pipe size. These modifications to
the BS test incorporating these higher pressures are
illustrated >>
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The following air test procedure is consistent
with that described in BS 8301 and the Water
Authorities Association publication "Sewers for
Adoption".
Click here to view larger diagram
- Seal the ends of the pipeline by means of expanding
or inflatable drain stoppers.
- Connect a 'U' gauge (manometer) to the test nipple
of the drain stopper by means of rubber tubing.
- Raise the internal pressure of the system until the 'U'
gauge indicates slightly more than 100mm. Purpose
made drain testing equipment is so calibrated that
the scale indicates the actual pressure in mm water
gauge.
- Allow about 5 minutes for stabilisation of the air
temperature (a 1° change in temperature is reflected
in a change in pressure of about 38mm on the
gauge).
- Adjust the pressure to 100mm by either introducing
further air or by bleeding off any excess pressure.
- Observe the fall in indicated pressure over a 5
minute test period. The residual pressure should be
not less than 75mm.
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