Assistant tank
It can control the water level, because there is a ball cock in the assistant tank, and all the cold water flow in via the assistant tank, so when the water level of the water tank is full, it will stop supplying water by closing the water valve. When the water in big water tank is not sufficient, it will open the water valve then continue to supply cold water.
It has different volume as well, the more the bigger the assistant tank, the higher pressure it can endure. Besides, it is more beautiful to match up with a suitable size water tank.
Model: 5L 8L 12L, 40L, 60L
Audited Supplier 
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