Type XA underdrain

Overview Specifications Industries & Applications Documentation & Tools


Product Features
  • Best uplift resistance - withstands uplift pressures up to 30 psi (2 bar)
  • Low profile of 8.25” (21cm)
  • 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
  • Handles for quick and easy installation, and snaps together for quick installation

Superior hold-down performance

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 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 XAunderdrain gives unprecedented flexibility and faster, affordable construction, all in a low profile underdrain. Longer laterals combined with all the standard flume layout options give more design flexibility than any other low profile underdrain.

The Type XA underdrain maintains its superior air and water distribution with new, patented interior baffles and dual water recovery channels. It also delivers superior uplift resistance (or hold-down) performance without the need for expensive mechanical anchors. The key is Xylem's patent-pending grout pocket, which fills with grout during installation and assures the Type XA underdrain will not lift from the filter floor, even if internal operating pressures reach 30 pounds-per-square-inch (2 bar).

The innovative 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 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.

Quick and easy to install

Specially engineered features enable simple construction or retrofits without compromising quality, reliability or performance. Snap-on/off handles allow two workers to easily maneuver blocks into position, and the blocks snap together with a bell and spigot seal, expediting installation.

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

The Type XA underdrain can be specified with Leopold I.M.S.® 1000 or 200 media retainers and factory-installed on the Type XA 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 and longer air/water backwash.



General Information
Underdrain type
Types of backwash suitable
Standards met
Flume types suitable
Construction type
Media retainer compatibility
Type XA underdrain
Potable Water, Wastewater, Desalination Pretreatment
Dual parallel lateral
Water only, sequential air followed by water, concurrent air/water and sustained air/water
NSF 61
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
Uplift pressure
Type XA underdrain
48" long x 11" wide x 8.25" high (1.2 m long x 0.28 m wide x 0.2 m high)
High Density Polyethylene (HDPE)
23.5 pounds (10.7 kilograms) approximate
2 - 6 scfm/sf (40 -110 m/hr)
Up to 30 gpm/sf (75 m/hr)
End feed 32 feet (9.75 m), Center feed 64 feet (19.5 m)
Less than +/- 5%
+/- 1/4" (6 mm)
2" (50 mm)
Yes, to reduce gravel plugging
Yes, two
Bell and Spigot
30 psi (2.0 bar)
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 XA 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 XA underdrain
Blower Casing
Type XA underdrain
Extruded High Impact Rigid PVC
Industries & Applications

Industries & Applications

Recommended Industries and Applications

Reuse > Tertiary Treatment Filtration
Media Filtration
Potable / Drinking Water > Filtration Media Filtration
Documentation & Tools