40
TECHNICAL
Air lock and water hammer
By
George Maritz , GK Water Solutions
As a plumber you may focus on building construction , building maintenance plumbing , civil construction projects or municipal pipeline maintenance .
In all the above , basic plumbing principles always apply and key aspects must be considered . I will briefly discuss an actual incident to show how air and water hammer can affect even the most hardened pipelines , and the consequences thereof .
Recently we were requested to investigate a municipal water main to a small town . The water treatment facility is next to a river and the clean , purified water is then pumped 16km to the command ( main ) water tank in the town for distribution to the residential areas . The steel pipe has a COD of 165mm and is pumped at a head of 600m . In this case the water did not reach the town and our client could not find any leak on the pipeline .
During our investigation we made some alarming observations such as air valves not working , some were removed and not replaced or repaired . We started with a visual inspection at the point ( height ) to where the water reached . The pipe is about 1.5m below ground and we could feel the ground shaking and hear the hammer inside the pipe . The echo was almost unbelievable .
We now understood the water was leaking from a lower point . We decided to go down into the riverbank and found our first leak next to the river . The water was not visible from the top and the view was blocked by vegetation . The water flowed underground into the river . After this leak was repaired , we also repaired some of the air valves and replaced another air valve . After all the repairs we had a water loss of 7.3Lt / s indicating another major leak on the pipeline . We found the leak using our water leak detection equipment as it was not visible from where we could see . The water flowed underground to the side of the mountain as the leak was at a height of about 400m . The steel pipe was blown-up like a balloon causing the pipe to burst . The non-functional air valves caused water hammer inside the pipe which was forced by the pumps resulting in the pipe failure . After the repair we bled the system to make sure no air was trapped for the water to be allowed through to the tank in town .
We know that trapped air is a plumbers ’ worst enemy and will result in pipe failure or water trapped in the air lock . Air release valves must be installed in the correct position and maintained to avoid damage to water systems .
Standards references are : SANS 10252 -1 Water supply and drainage for buildings-water supply for buildings . SANS 1200 Civil engineering ( L , LB , LD , LF ) PA
All images : B H Maritz
Burst pipe due to trapped air and water hammer . Milky white water indicating compressed air . Milky white water indicating compressed air .
www . plumbingafrica . co . za @ plumbingonline @ plumbingonline @ PlumbingAfricaOnline March 2021 Volume 27 I Number 1