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Underground Drainage Chambers

Inspection Chambers / Access Chambers

Inspection chambers and Access chambers are essential to aid with the correct operation of a drainage system. They allow access to the pipe work to clear any blockages. They also allow up to 5 different flows to combine into one to cut down on pipes used. Traditionally these were brick built and known as man hole covers, as they required a person to physically climb down and sort any issues. Now these are much smaller, lighter PVC products that don’t permit physical entrance.

Inspection chambers should be used at least every 22m, and generally should be used at every junction connecting to the main drain flow or where a pipe bends more than 30° in a horizontal direction.


Chambers should be positioned so that the main flow continues straight through without making any directional changes.

There are two main different chambers. The Mini Access Chamber (MAC) has a diameter of 300mm and the Large Inspection Chamber (LIC) has a diameter of 450mm.

The MAC can be used to a maximum depth of 600mm with the use of a choice of 100mm or 200mm chamber risers. These risers make planning and installing a underground system easier.  To futher simply the installation, the MAC is available with variable angle inlets. These allow for pipe work to be connected to the chamber, even if they dont 100% line up with the inlets. 10° of movement in any direction can be a life saver in tight installation conditions. Of course we can also supply MAC’s with rigid inlets too.

inspection chambers inspection chambers

The larger 450mm Inspection Chamber has the ability to be used at depths of up to 1200mm, and a huge 3000mm when used in conjunction with a 350mm reduced opening cover for safety, basically a smaller diameter plastic insert, as its considered a small child could not fall down one. It can be supplied with either 5 rigid inlets or as the MAC above, can come with 5 variable inlets to easy installation.


Both chambers need to be installed on a suitable solid base , and backfilled with the material that was dug out, all the way to 50mm below the finished surface. The frame and cover are then placed into a bed of concrete at the required level. The frame will then be screwed into the chamber riser to secure everything together and finally the lid screwed down with captive screws. It will then be impossible to remove the lid without undoing the screws.

Should bends in the pipework be needed around the point of a chamber, these should be installed before the chamber, you should not try to change the direction of the main flow inside the chamber as self cleaning cannot be guaranteed and you may create a point that may cause blockages.

Any unused sockets of any chamber need to be capped.

There is a number of manhole covers that can be installed at the top of the chambers. These range on the desired finish. There are square and round covers in plastic and cast iron and a block paving cover for a block paving finish.