Cobblestone media, also called gravel media or support-layer media, is a bedding material purpose-made for waterworks and filters. It is produced from natural river cobblestone by quarrying, screening, water washing to remove impurities and grading; it can also be made by crushing and rounding quartz ore. Standard: CJ/T 43-2005 Filter Media for Water Treatment.
2. Physical and Chemical Properties
Main constituent: silica, SiO₂ ≥ 98%.
Appearance: rounded granules with no sharp edges and a smooth surface; predominantly off-white and white.
Mud content ≤ 0.1%; free of mica and organic impurities; chemically stable, releasing no harmful substances across a wide pH range; non-toxic and odourless.
3. Common Grain Sizes (support layers graded from fine at the top to coarse at the bottom)
2-4 mm, 4-8 mm, 8-16 mm, 16-32 mm, 32-64 mm
Support layers in a filter must be laid in separate graded courses with transitions between them; a single grain size must not be used.
4. Main Functions (Waterworks Filters)
Support: carries the weight of the fine media above it (quartz sand, anthracite) and prevents fine media from sinking into the filter caps, filter plates and distribution pipework below, avoiding sand loss and blockage of the collection system.
Uniform water and air distribution (backwash): backwash water and air spread evenly after passing through the cobblestone layer, eliminating local high-velocity scouring and preventing preferential flow and bed disturbance.
Coarse filtration: the large voids retain bulky impurities and reduce the load on the media above.
5. Applications
Support bedding for conventional rapid filters, siphon filters and V-type filters in waterworks.
Bottom bedding for multi-media filters and ion-exchange vessels.
Bedding for industrial circulating water and advanced wastewater filtration.
Support layer at the base of aerated biological filters.
6. Installation Notes
Wash the media clean before laying; it must be free of soil and dust.
Lay the courses strictly in order from fine at the top to coarse at the bottom, levelling each course.
Filters with high-resistance distribution systems must have a cobblestone support layer; low-resistance distribution with long-stem filter head and plate systems may be simplified as required.
