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Product Features
  • Ideal for shallow filters
  • Low profile of 8” (20cm)
  • Can be designed for center and front flumes
  • Superior air and water distribution for effective backwash giving longer filter runs and lower operating costs
  • Easy handling - snap together for quick installation 

Ideal for shallow filters

Underdrains collect filtered water during the filter run, and distribute air and water during the backwash cycle. Providing cleaner filters mean longer filter runs and higher water efficiency, more product water, and less waste. This lowers your operating costs per gallon or liter of filtered water. All Leopold underdrains deliver the superior performance that has made the Leopold underdrain the industry leader.

The Leopold Type SL® underdrain features a low profile of 8” (20cm), making it the perfect choice for shallow filters.

The dual parallel lateral design and the water recovery channels, both developed by Leopold, give even distribution with less than +/-5% maldistribution and no dead zones.

The Type SL underdrain can be specified with Leopold I.M.S.® 1000 or 200 media retainers and factory-installed on the Type SL underdrain to save time at installation. The I.M.S. media retainers replace up to 14 inches (36 cm) of gravel media support allowing for the same media depth in less vertical space or longer air/water backwash.

The air flow adjustability allows for more control and saves energy and water. Air scour rate can be adjusted from 2 to 5 scfm/sq.ft. (0.6 to 1.5 m/min), enabling collapse pulse cleaning during concurrent air/water backwash with various media configurations. Air scour provides higher shear forces and cleaner media, with less wastewater generation.

Easy handling - snaps together for quick installation

The Type SL underdrain is also equipped with internal baffles that can be installed to a level tolerance of ±1/4 inch. This is ideal for older installations, where construction tolerances aren't as rigid. Installation tolerances that are more forgiving also make for simpler installations and lower filter construction costs.

In addition, the Grout-Tite® Bridge prevents grout from entering the flume, so there's no costly cleanup.



General Information
Type SL underdrain
Potable Water, Wastewater, Desalination Pretreatment
Underdrain type
Dual parallel lateral
Types of backwash suitable
Water only, sequential air followed by water, concurrent air/water and sustained air/water
Standards met
NSF 61, British DWI, French
Flume types suitable
Flat Bottom Flume, Front Flume, Center Flume, H-Flume
Construction type
New or existing regardless of current underdrain type
Media retainer compatibility
Gravel, I.M.S 200 media retainer, I.M.S 1000 media retainer
System Components
Type SL underdrain
Nominal dimensions
48" long x 11" wide x 8" high (1.2 m long x 0.28 m wide x 0.2 m high)
System components material
High Density Polyethylene (HDPE)
19 pounds (8.6 kilograms) approximate
Air flow range
2 - 6 scfm/sf (40 -110 m/hr)
Water flow
Up to 30 gpm/sf (75 m/hr)
Maximum lateral length
End feed 24 feet (7.3 m), Center feed 48 feet (14.6 m)
Water mal-distribution
Less than +/- 5%
Level tolerance
+/- 1/4" (6 mm)
Orifice spacing
2" (50 mm)
Orifice recessed for gravel
Yes, to reduce gravel plugging
Secondary baffles
Water recovery channel
Yes, one in the center
Underdrain block connection
Bell and spigot
Technical Details
Type SL underdrain
Weight (lbs./sq. ft)
Approximatly 6.3
Weight (kg/m2)
Standard block dimensions (in / ft)
11" wide x 6" high x up to 38' long
Standard block dimensions (cm / m)
27cm wide x 15.2cm high x up to 11.58m long
Installed structural capacity (kg/m2)
7000 (Minimum evenly distributed load)
Burst strength (psi)
Burst strength (KPa)
Lateral Length
Type SL underdrain
Height (inches)
Height (cm)
Center flume (feet)
Center flume (meters)
Front flume (feet)
Front flume (meters)
Wall feed/H flume (feet)
Wall feed/H flume (meters)
Leopold flat bottom (feet)
Leopold flat bottom (meters)
Blower Casing
Type SL underdrain
Extruded High Impact Rigid PVC
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Documentation & Tools

Documentation & Tools