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Underground Drainage - Basic Principles

Cutting and Joining Pipes 

Pipes can be cut with a standard, fine-toothed saw. Whenever a pipe is cut the end must be chamfered, and cleaned of any swarf, dirt or grit. Chamfering can be achieved using a medium file or rasp. The chamfered end of the pipe and the ring seal of the fitting should be lubricated using SG100 lubricant. Ensuring the pipe is square to the fitting, push the pipe fully into the socket, and then withdraw 10mm (this allows for any expansion or ground movement). The joint is now complete.

Laying Drainage Pipes

Underground Drainage Pipes should be laid in a trench that is 300mm wider than the pipe itself (i.e. 410mm for 110mm pipes). The trench may be trimmed and used as the pipe bed if it is of a suitable material (fine soil with no large stones or flints). It is more usual though for granular material such as pea shingle no larger than 10mm to be used to construct the pipe bed. The "as dug" material can also be used as a sidefill and backfill, providing again that it is suitable, if not pea shingle should be used. At least 300mm of of material should be replaced over the top of the pipe before mechanical compaction can be undertaken. When there is any danger that the pipe may be in danger of contact (for example when gardening) it should be protected by a paving slab cover.

Pipe Falls

110mm Underground Drainage Pipes in domestic properties with 5 or less WC's connected to the system should be laid to a fall of 1 in 40. The fall must not exceeded as it enables the system to be self-cleansing. If more than 5 WC's are connected the fall can be reduced to 1 in 80. If in you are in any doubt you should seek advice from your appropriate local authority.

Adjustable bends

Adjustable bends are ideal when making connections new into an existing drainage system. This cleverly designed fitting twists at two separate points, allowing it to be completely adjustable to all angles between 0 and 90 degrees, enabling new pipe runs to be perfectly aligned to the existing system and minimising the amount of other fittings that are required.

Connections to above ground drainage

Our Drainage System is fully compatible with our Above Ground Soil and Vent System, enabling a direct connection to made without the use of adaptors. When connecting rainwater pipes directly to the drain, the D96 adaptor should be used. The D95 adaptor should be used when connecting 32mm, 40mm and 50mm waste pipes to the drainage system.

Adaptors to other materials

Our D102 and D103 flexible adaptors enable a wide range of materials such as clay, cast iron and pitch fibre to be connected to PVC Drainage. Cast Iron Soil Pipes can be connected to PVC by use of the SP140 adaptor.

Testing drains

All Drainage Installations should be tested in accordance with the appropriate approving authority. If in doubt reference should be made to current editions of Building Regulations (Approved Document H).


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