Clay Drainage Testing

Testing the pipeline for water tightness

When laying Naylor Densleeve or Denseal pipes, it may be convenient to check that all is in order by applying interim air tests to progressive lengths of pipeline as work proceeds.

Once a pipeline has been laid an air or water test may be carried out in accordance with BS EN1610, as detailed below.

Air Test

  1. Fix air-tight stoppers at the ends of the pipeline, after checking that they are clean and well-fitting. Connect a manometer to one of the stoppers.
  2. Blow or pump air into the pipeline until a pressure slightly more than the required air test pressure is indicated on the manometer. After allowing 5 minutes for the temperature to stabilise, adjust to the required pressure and commence the test.
  3. (a) If the measured drop is less than the allowable drop then the test is passed (see table).

Note: The test pressure LA is the same as that previously used in the UK except that the test period is increased for sizes above DN225, as shown.

Test Method: Test Pressure mbar (kPa): Allowable Drop mbar (kPa):
LA 10 (1) 2.5 (0.25)
Test period in minutes
DN100 DN200 DN300 DN400 DN600
5 5 7 10 14
  1. (b) If the measured drop exceeds the allowable loss, carefully check the testing apparatus and stoppers and examine the pipes and joints for leakage. If a defect is discovered, remedy it and re-test.

If this test does not reveal a defect, apply a water test.

The above standards do not regard an air test alone as sufficient grounds for rejection and it is recommended that a water test should be applied in the event of apparent failure to meet the air test. An apparent failure of air test can be due to causes other than defects in the pipeline; for example, changes in ambient temperature.

Water Test

1 At the upstream end of the pipeline to be tested, add a 90° bend and sufficient vertical pipes to provide the required head of water. BS EN1610 requires a minimum 1.0m (10kPa) head of water at the high end with a maximum of 5m (50kPa) at the lower end. Both heads above the pipe crown. In cases of very steep gradients, it may be necessary to test the pipe in stages, in order to comply with these limitations.

2. Tighten stoppers at the lower end of the pipeline and at open branches, after checking that they are clean and well-fitting.

3. Strut the ends of the pipeline and the 90° bend to prevent movement and then fill the line with water.

4 Inspect the pipeline for any obvious leaks and remedy any defects. There will be an initial fall of the water level due to absorption and the displacement of trapped air.

5 After at least one hour, top up to the maximum test head, a longer period may be allowed in extremely dry conditions. The loss of water over a period of 30 minutes should then be measured by adding water from a measuring vessel at regular intervals of 10 minutes and noting the quantity required to maintain the original water level. The test is accepted if the water added does not exceed 0.15l/m² of internal wetted area over a 30 minute period, for pipelines. Higher limits are set for pipelines including manholes and inspection chambers.

Further information
See BS EN1610 and the Clay Pipe Development Association Ltd booklets Specification, Design and Construction and Testing of Drains & Sewers (Water & Air Tests).


Any selected or granular fill must be carefully hand-compacted in layers not exceeding 150mm to complete the pipeline surround. Place and compact this fill equally on both sides of the pipeline to prevent displacement.

Slice with a spade around the barrels to form a cradle for the pipes. This work is important, as the pipeline derives some of its strength from a properly constructed bedding.

The trench must be backfilled to at least 300mm above the crown of the pipes before any power-ramming takes place. Backfill should then be well-compacted in layers not exceeding 300mm.

As backfilling proceeds withdraw timber and trench sheeting in stages to avoid disturbing the pipeline or the creation of voids within the bedding and surround.

Site Traffic

Site traffic should not pass over buried pipelines before backfilling has been completed and the final surface constructed.

Overloading by unavoidable site traffic can be prevented by bridging the trench with steel plates, timber sleepers or other temporary protection.