In the UK, high pressure water jetting is widely used to clean and mostly to clear blocked sewer pipelines – often as an emergency operation. The European Standard BS EN14654-1:2014 Management and control of operational activities in drain and sewer systems outside buildings, Part1: Cleaning, states that “Maximum safe working pressures to avoid damage will vary according to the material of the pipe, condition of the pipe and type of nozzle”. Risk of damage to the pipeline can be reduced if the jetting nozzle is kept moving and the direction of the jet does not focus on the wall of the pipe. Damage in this way may be avoidable, but the risk of damage increases where there is an obstruction within the pipeline and the jetting nozzle cannot pass through the blockage
In 2005 the WRc published the Second Edition of the Sewer Jetting Code of Practice. This document provides guidance on good working practice when using high pressure water jetting equipment. The code establishes a maximum jetting pressure for pipeline materials, varying from 1500psi for brick sewers up to 5000psi for concrete pipelines – see Table 1 below.
Table 1: Water jetting pressure maximum limits for different pipe materials from the Water Jetting Code of Practice.
It is generally accepted that smaller diameter pipes are most effectively cleaned with pressure as the source of energy within the pipes. In theory, if the code is closely followed, it should prevent damage to the fabric of drains and sewers from occurring, but the huge difference in maximum jetting pressures from 5000psi for concrete down to 1500psi for brick, can potentially lead to confusion. It would make sense if a maximum jetting pressure was applied consistently nationwide at a value known to result in effective cleaning and clearing of blockages. Sadly, the required pressure to shift some stubborn blockages exceeds the resilience of some materials and damage to the sewer is more likely unless the operation is carried out to the textbook and with extreme care.
For larger diameter pipelines there is an argument that flushing the blockage through using a large volume of water at lower pressure is an alternative to high pressure jetting. However, to generate a high flow rate, access to a drinking water hydrant or a large capacity water tanker will be required. This can be a more expensive, time consuming, wasteful and less environmentally friendly solution than using lower volumes of water jetted at higher pressure. It is important that users understand the differences in the resilience of different pipeline materials to high pressure water jetting and the implications of using different cleaning and blockage clearing methods.
BPDA has an extensive library of useful information and guidance publications for designers, installers and asset owners. They are available to download free of charge from the BPDA’s website. The site also holds a comprehensive and searchable FAQ section and an online enquiry facility; go to www.precastdrainage.co.uk