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TECHNICAL
How should my under-basin geyser be installed ?
By Patrick Gordon of Calafrica ( technical @ calafrica . co . za )
How often do we see small water heaters installed in office kitchens or doctors ’ rooms ? The problem with these installations is that the instructions that come with them are written for overseas installations . The regulations and means of installation in these countries varies greatly from our regulations .
These water heaters are often installed as pressure vessels because they are rated for very high pressures , and the manufacturers assure us that they can handle these pressures . This is all good and well , but if we install them as pressure vessels , we need to abide by the national regulations that regulate these installations . SANS 10254 requires that all installations have a maximum of 600kPa pressure . It also requires that all these hot water cylinders be installed with a temperature and pressure safety valve , two vacuum breakers , an expansion relief valve , and a pressure reducing valve . You also need to issue a Certificate of Compliance for the installation .
In many cases the installer has tried to make the installation compliant by adding these ancillary valves but always ending with a non-compliant installation .
So , does that mean that we should not use these units ? No , they are great for installations that have a user point that is far from a normal hot water supply .
Most of the manufacturers of these units also offer a mixer that has been specially designed to work along with the heater . The difference between these mixers and the normal mixers is that they have three supply pipes . These mixers are ported in such a way that if it is correctly installed the water heater will always be venting to the atmosphere . The first pipe is connected to the cold-water supply ( this can be without a Pressure Control Valve ). The next pipe is connected to the cold-water inlet of the Heater , and the third pipe is connected to the hot-water outlet on the heater . The way that this works is if the hot-water side of the mixer is opened it takes cold water from the supply and pushes it into the heater . When this happens the increase of pressure is immediately discharged via the third pipe to the outlet / spout of the mixer and no pressure is built up within the terminal installation . Any expansion that occurs during the heating process is also immediately discharged via the mixer outlet .
If the installation is done this way , it alleviates the need for any ancillary valves on the installation . This installation does not need extra relief valves to be compliant and is completely within the limitations of the law . PA
How do we then make this installation compliant ?
Typical open vent mixing control valve unit for under-sink water heaters .
www . plumbingafrica . co . za @ plumbingonline @ plumbingonline @ PlumbingAfricaOnline November 2021 Volume 27 I Number 9