Type S underdrain

Overview Specifications Industries & Applications Documentation & Tools


Product Features
  • Uniform distribution of air and water even in extra-long lengths
  • Standard profile of 12” (30cm)
  • Can be designed for wall-feed applications as well as center flume, front flume and Leopold Flat Bottom flume
  • Superior air and water distribution for effective backwash giving longer filter runs and lower operating costs
  • Easy handling - snaps together for quick installation

Setting the standard

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 S® underdrain is an HDPE underdrain, designed for strength and corrosion resistance. It offers the most design flexibility working with the different combinations of lateral lengths as well as different flume configurations. It is ideal for installations requiring longer laterals.

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 S underdrain can be specified with Leopold I.M.S.® 1000 or 200 media retainers and factory-installed on the Type S 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.

Ideal for existing, older installations

The Leopold Type S 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
Underdrain type
Types of backwash suitable
Standards met
Flume types suitable
Construction type
Media retainer compatibility
Type S underdrain
Potable Water, Wastewater, Desalination Pretreatment
Dual parallel lateral
Water only, sequential air followed by water, concurrent air/water and sustained air/water
NSF 60, British DWI, French
Flat Bottom Flume, Front Flume, Center Flume, H-Flume
New or existing regardless of current underdrain type
Gravel, I.M.S 200 media retainer, I.M.S 1000 media retainer
System Components
Nominal dimensions
System components material
Air flow range
Water flow
Maximum lateral length
Water mal-distribution
Level tolerance
Orifice spacing
Orifice recessed for gravel
Secondary baffles
Water recovery channel
Underdrain block connection
Type S underdrain
48" long x 11" wide x 12" high (1.2 m long x 0.28 m wide x 0.3 m high)
High Density Polyethylene (HDPE)
25 pounds (11 kilograms) approximate
2 - 6 scfm/sf (40 -110 m/hr)
Up to 30 gpm/sf (75 m/hr)
End feed 48 feet (14.6 m), Center feed 96 feet (29 m)
Less than +/- 5%
+/- 1/4" (6 mm)
2" (50 mm)
Yes, to reduce gravel plugging
Yes, one in the center
Bell and Spigot
Technical Details
Weight (lbs./sq. ft)
Weight (kg/m2)
Standard block dimensions (in / ft)
Standard block dimensions (cm / m)
Installed structural capacity (kg/m2)
Burst strength (psi)
Burst strength (KPa)
Type S underdrain
Approximatly 6.3
11" wide x 6" high x up to 38' long
27cm wide x 15.2cm high x up to 11.58m long
7000 (Minimum evenly distributed load)
Lateral Length
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)
Type S underdrain
Blower Casing
Type S underdrain
Extruded High Impact Rigid PVC
Industries & Applications

Industries & Applications

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Documentation & Tools