Drain Testing: A Quick Guide

So, you have a problem with your drains and call an expert to out to test them. How exactly does the drain testing process work?

If you’re curious about drain testing, we’ve put together a quick guide to help you understand what goes on.

We tend to use two methods for drain leakage investigations:

1.       Air Test – for single pipes or individual drain runs. The air pressure test is effective, but it can only be used to test a length of a drain that can be capped at both ends.

2.       Water Drop Test – for complete drainage systems including chambers and gullies. This is a more involved test; it can be used to test a whole drainage system, even gullies and chambers.

How an Air Test Works

First, airtight plugs are inserted in order to isolate the section of pipework that’s being tested. Using a drain pressure gauge, the pressure is set to 110mm head for 5 minutes. Next, the pressure is adjusted to a 100 mm head reading of the pressure gauge and after 5 minutes any change in head is measured. Over this 5 minute period, the maximum allowable loss is 5 minutes.

To find out more about the air test, you can find more details in BS EN 1610 and in Building Regulations Approved Document H.

How a Water Drop Test Works

The ‘drop’ test is a low-pressure method of drain testing. It works by isolating the downstream end of the drain with a bung, before charging the system with water and monitoring the water levels either at a manhole or a pipe access point.

By filling a chamber to the top with water, no additional pressure should be imposed during this drop test. For this reason, the head of water should be minimal and, where practical, should be limited to 1.5 metres, measured from the lowest invert level of the drain being tested.

After water is filled to the top of the manhole benching, it should be left to soak for 5 minutes before begin topped up. It should be left to charge for 10 minutes more, before topping up again once the changes have been recorded. We’ve highlighted the values of leakage over a 10 minute period in our lovely table below.

Acceptable Leakage Rates (measured in litres in 10 minutes)

Diameter   Length of drain (m)
 5-10 10-20 20-30
100 0.2 0.4 0.6
150 0.3 0.6 0.9
200 0.4 0.8 1.3
225 0.5 0.9 1.4

You may be wondering what happens with drains less than 5 metres long. In this case, it is a matter of judgement whether the leakage is significant. Generally, a drop of less than 25mm in 10 minutes is acceptable; however, if there is damage to the property as a result of the leak, there is a problem!

Want more information about how we test drains? Feel free to get in touch with us at Happy Drains.