Filter Support Gravel
Filter support gravel is the graded quartz stone that sits on the underdrain of a sand or multimedia filter. It holds the finer media in place, spreads backwash water evenly and stops sand being lost through the nozzles or laterals. We supply washed silica quartz gravel in bags and bulk bags, delivered from Johannesburg and Cape Town.
Support gravel grades
| Grade | Typical position | Order |
|---|---|---|
| 1 – 3 mm | Top support layer, directly under fine sand | Buy 1 – 3 mm |
| 3 – 5 mm | Second support layer | Buy 3 – 5 mm |
| Coarse filter quartz | Middle support layers in larger filters | Buy coarse 40 kg |
| 13 mm | Bottom layer over laterals and nozzles | Buy 13 mm |
Coarser gravel for large municipal underdrains can be supplied on request.
Typical specification
| Property | Typical value |
|---|---|
| Material | Washed silica quartz |
| SiO2 | up to 98.5% |
| Hardness (Mohs) | 7 |
| Grain shape | Rounded to sub-angular |
| Packaging | 40 kg bags and 1-ton bulk bags |
How to layer support gravel
Place gravel from coarsest at the bottom to finest at the top, with each layer roughly 75 – 150 mm deep. Each layer’s grains should be no more than about four times the size of the layer above it, so finer media cannot migrate down. Your OEM or designer’s drawing sets the final depths.
Applications
- Municipal rapid gravity and pressure filters
- Industrial and mining process water filters
- Borehole and irrigation sand filters
- Large pool and commercial aquatic filters
Frequently asked questions
Do I need to replace gravel when I change the sand?
Not always. Gravel lasts much longer than sand, but if it is fouled, cemented or mixed with sand it should be replaced at the same time.
Can you supply gravel and media together?
Yes. We supply complete beds of filter sand, hydro anthracite, garnet and gravel, labelled per layer. See all water filtration media.