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Minimum Diameter for Overflow Drain for Cold Water Tank

Postby chipbag » Tue Mar 10, 2020 7:18 pm

I have a cold water tank in a basement (1230 litres) with a ball float inside. There is a overflow pipe to the side and immediately below there is what I would describe as a overflow drain which runs under the floor.

Is there a minimum diameter that the drain pipe should be
Should the overflow pipe run directly into the drain or is it acceptable to be about 36 inches above and to let it free fall into the drain
Should there be a plastic grate on top of the over flow drain

Thanks in advance.
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Postby Barbastelle » Tue May 04, 2021 12:19 am

The usual size for a cold water tank for an overflow outlet is 22mm pipe of plastic. But saying that if you can fit a larger diameter pipe do so.
Your cold water tank should have a lid fitted with an air vent with filter as on a tea strainer fitted to the lid. The strainer would be in a larger exit pipe from the tank reducing down a bit to the overflow pipe.
Also a strainer fitted in the outlet overflow pipe. These are to stop files and other insects entering the tank.
All this is under Bylaw 30. So you will need a Bylaw 30 tank kit.
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