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Anthracite below troughs?

Anthracite below troughs?

Anthracite below troughs?

(OP)
What is the correct depth that anthracite media should be below the troughs in a gravity filter?  I'm thinking 4"-6".

RE: Anthracite below troughs?

If it is anthracite, I assume it is a dual media filter.  You need to work out the bed expansion for all the types of media during the backwash, or the re-grade wash if you are doing one.  Once you have the bed expansion, assuming you have a reasonably low weir loading rate, 100mm-150mm above the top of the expanded bed should be alright.

RE: Anthracite below troughs?

4'6" sounds a little on the high side. Sand filters expand about 30% bed of depth and anthracite filters expand about 40% of bed depth at maximum backwash rates.

Anthracite filters would need a minimum freeboard of approximately 50% anthracite bed depth.

http://www.performancewater.com/catalog_product.aspx?prod_id=1

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