The Bottom Layer Decides the Filter: Four Checks Before Buying 4–8 Mesh Garnet

RUMMANA 4–8 mesh garnet is available to water treatment contractors, filter builders and filter media distributors worldwide, supplied by Meritus Technology from Shanghai.

Most of the attention in a multimedia filter goes to the top of the bed: anthracite depth, sand effective size and loading rates. The layer at the bottom is specified once, bought on price and forgotten, until the bed starts to move.

Why garnet goes at the bottom

A multimedia filter only works if its layers return to order after every backwash, and the media re-settle by weight. Anthracite, at a specific gravity of roughly 1.4 to 1.7, settles last and stays on top. Silica sand, at about 2.65, sits beneath it. Garnet, at 3.8 to 4.1, is heavier than both, so it settles first and stays down. That density is why coarse garnet is used as the support and underbed layer: it holds the finer media above the underdrain and resists being lifted into the layers above.

What goes wrong when the bottom layer is wrong

• Fines from the support layer migrate upward and blur the interface with the layer above.
• The first filtered water after commissioning is turbid, from media that was not washed.
• Media mix or are lost after an aggressive backwash.
• Grains slowly dissolve or break down in service.

Most of these trace back to a handful of numbers on the data sheet.

Four checks before you order

1. Grading, not just the mesh name. Ask for the retained-weight distribution. RUMMANA 4–8 SPL is screened to 2.36–4.75 mm, typically 92 percent within range, with oversize below 1 percent and undersize held below 8 percent.
2. Specific gravity and hardness. Density is the reason to use garnet at all. RUMMANA runs at 3.8–4.1 g/cm³, with Mohs hardness 7.5–8.0 so grains resist wear over repeated backwash cycles.
3. Acid solubility. Media that dissolve change size and release material into the water. RUMMANA acid solubility (HCl) is below 1.0 percent.
4. Cleanliness. RUMMANA 4–8 is washed and magnetically separated, with moisture at or below 0.2 percent and chloride at or below 25 ppm, no added chemicals, non-toxic and non-radioactive.

Two cuts, and where they go

4–8 mesh for general support layers, ballast and weighting, and 4–8 SPL, the tighter screen with undersize held below 8 percent, for filters where a clean layer interface matters. Typical uses are multimedia and pressure filters for drinking water, process water and wastewater, media filters ahead of RO and desalination, and filter media distributors supplying their local water treatment trade.

RUMMANA is supplied from the mine face to shipment, with coarse 4–8 grades and the finer abrasive grades from one source, from a single container to programme volumes. Technical data sheet: www.rummanagrit.com.

Related: garnet filtration media.

Meritus Technology Shanghai
Email: sales@meritustech.com
Phone / WhatsApp: +86 134 8206 1802
www.meritustech.com