header tank: A raised tank or hopper that maintains a constant pressure or supply to a system, especially the small tank that supplies water to a central heating system.

food grade https://foodgradematerials.wordpress.com/2013/05/20/food-gra...

food grade=
المادة المصنوع منها الخزان من نوعية ملائمة لتخزين الطعام
e.g. special stainless steel

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Note added at 5 hrs (2016-08-23 04:26:38 GMT)
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header tank =
خزان رئيسي