Site Tests

Site Tests

Air & Water Site 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 separately tested.

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-

  1. obstructions and debris,
  2. structural soundness of pipes,
  3. joints properly sealed,
  4. 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

To test the pipeline:-

  1. 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.
  2. Fill the system with water ensuring all the air has been expelled.
  3. 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.
  4. Apply required test head at the upper end by means of a flexible pipe leading from a graduated container or stand pipe.
  5. 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.
  6. 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.

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:-

  1. leakage from test equipment
  2. trapped air,
  3. leakage from joints, e.g., displaced ring,
  4. leakage from damaged or defective pipe.

Click here to view larger diagram


Air Test
The air test is very searching and is more convenient than the water testSS TABLE 5, 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.

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:-

  1. The BS air test specifies a constant requirement regardless of diameter and length of the pipeline.
  2. The air test is relatively more sever on smaller pipe diameters.
  3. Pipe wall dampness affects air test results, particularly on smaller diameter pipes and at the low pressure specified.

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 >>

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

  1. Seal the ends of the pipeline by means of expanding or inflatable drain stoppers.
  2. Connect a ‘U’ gauge (manometer) to the test nipple of the drain stopper by means of rubber tubing.
  3. 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.
  4. 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).
  5. Adjust the pressure to 100mm by either introducing further air or by bleeding off any excess pressure.
  6. Observe the fall in indicated pressure over a 5 minute test period. The residual pressure should be not less than 75mm.


Case Studies

Titanic Signature Project, Belfast

Harbour Way Project, Port Talbot, Wales

Bedale, Aiskew and Leeming Bar Bypass, North Yorkshire

Rotherhithe, London – Thames Water

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