Concrete Filter Plate · Technical Reference & Specifications

What a concrete filter plate is

A concrete filter plate is a flat precast concrete panel that forms the bottom — the nozzle deck — of a water or wastewater filter. Each plate carries a regular grid of holes or cast-in sockets, and a filter nozzle is fitted into every position so that backwash water and process air are distributed evenly over the whole filter area and collected again during filtration.

The plates are cast on a casting jig, cured, and then lifted into the filter basin on site. Inside the tank they are bedded on mortar strips and levelled individually, the joints between plates are sealed, and the filter nozzles are fitted. The support layer of graded media and the filter bed itself are then placed on top of the finished deck.

Because the panel is precast, the tank floor is assembled from finished, checked elements rather than poured in place. This suits both new filters and the reconstruction of an existing filter bottom, where the old deck is broken out and replaced with new plates set to a common level.

Plate construction and nozzle layout

The plate is a reinforced concrete panel, cast in a steel mould. Its two working features are the hole grid and the way the nozzles are held in it.

• Plain hole grid. The plate is cast with round holes at the design spacing; the filter nozzles are fitted and fixed into these holes on site with their own sealing arrangement.
• Cast-in sockets. Threaded or moulded sockets are set out on the jig before the pour, so they are cast into the plate at the design grid spacing and at a common level; the nozzles are then screwed or pushed into the sockets and can be replaced individually later.
• Grid spacing. Hole spacing, hole diameter and the number of positions per plate follow the nozzle selected and the distribution the filter is designed for.
• Reinforcement and lifting. The plate is reinforced for handling and for the service loads on the filter bottom, and lifting points are provided so it can be craned into position without damage.
• Plate shape. Plates are made square or rectangular; the plan is completed at the tank perimeter with plates cut or cast to suit the wall line and the tank corners.

The exact hole pattern, socket type and reinforcement are set by the project drawing and the nozzle chosen — they are confirmed per order rather than taken from a fixed catalogue.

How a precast filter bottom is installed

The method is fixed by the contractor's method statement; the sequence below describes how the plates are normally laid.

1. Basin preparation. The filter is drained and cleaned, and the existing bottom or the structural slab is checked for level and soundness and repaired where needed.
2. Bedding strips. Mortar bedding strips are laid on the tank floor along the plate supports, to a level that sets the finished nozzle deck height.
3. Bedding and levelling. The plates are lifted in and bedded one by one, each plate being set to the line and level of the deck before the bedding sets.
4. Joints. The gaps between adjacent plates are filled and finished so the deck reads as one continuous, tightly closed surface with no step at the joints.
5. Hole and socket check. Every hole or socket is checked for position, level and clearance — and cleared of mortar or debris — before the nozzles are fitted.
6. Nozzle installation. The filter nozzles are fitted into the plate, checked for tightness and for a common top level across the deck.
7. Support layer and media. The graded support layer is placed on the finished deck, followed by the filter media, with the nozzle height and the media grading matched to the filtration duty.

Filter nozzles are supplied separately and matched to the plate; media for the support layer and the filter bed is quoted to suit the filtration duty.

Precast plates or a cast-in-place bottom

Both options give a filter a concrete nozzle deck; the choice is usually driven by the tank, the programme and the access.

Related: BS Cast-in-place Filter Plate — the monolithic poured filter bottom.

Specification data

Configuration is confirmed against the project drawing. Parameters marked on request are quoted for the specific plate, nozzle grid and tank rather than taken from a fixed catalogue.

No filtration performance figures are published for the plate itself: filtration performance is set by the media, the nozzle selection and the filter design, not by the concrete panel.

Where concrete filter plates are used

• Rapid gravity filters and V-type filter bottoms in waterworks
• Biological aerated filters (BAF) and denitrification filters
• Activated carbon contactors and adsorption filters
• Iron and manganese removal filters
• Tertiary and polishing filtration in municipal and industrial plants
• Seawater and desalination pre-treatment filtration
• Filter upgrading and reconstruction, including replacement of a failed or uneven filter bottom

What we need to quote

Send the following and we will come back with the plate layout, the matching nozzles and the export packing:

• Filter tank plan, with internal dimensions and the wall line
• Plate size required, if it is already fixed, or the tank dimensions so we can propose sizes
• Nozzle type and the required nozzle grid spacing, with hole diameter or socket thread
• Plate thickness, concrete grade and reinforcement requirement, if already specified
• Quantity, project destination and required delivery date

If those details are not settled yet, tell us the filter duty and the tank size instead — we will work from that.

Related pages

• Concrete Filter Plate — product page with gallery
• BS Cast-in-place Filter Plate — monolithic poured filter bottom
• ABS Filter Nozzle — tower and mushroom nozzles for filter plates
• Denitrification Filter Brick — moulded air and water distribution block

Compiled from our production and site records for precast concrete filter plates. Sizes and parameters marked on request are confirmed against the specific tank drawing before quotation.