Tough Down Under

A new low-profile underdrain system is designed for ease of installation, high durability and uniform performance.
Tough Down Under
The FilterWorx filtration system

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Water treatment media filter performance starts with proper installation. A new low-profile underdrain system from Leopold – a Xylem Brand, is part of a complete filter package that aims to give water plants reliable, long-lasting results while simplifying installation and lowering construction costs.

The Type XA underdrain is designed to make installation more forgiving in new construction and retrofits. It has features that help contractors work more efficiently and that in operation enable uniform backwash and water distribution. Brian Bates, product manager and innovation champion for filtration and clarification with Leopold, talked about the offering in an interview with Water System Operator.

wso: What is the advantage of a low-profile underdrain?

Bates: The primary reason for a low-profile underdrain is to serve the retrofit market. Where you have a shallow tank to work with, the lower the underdrain profile, the more flexibility you have for media selection or driving head. We already had a low-profile underdrain in the Leopold Type SL, but its use was limited to 16-foot laterals. The Type XA accommodates 32-foot laterals, so we can build larger filters in low-profile settings.

wso: What makes this underdrain easy to install?

Bates: First, it has handles that can quickly pop on and pop off. That helps contractors when installing the 32-foot laterals. They can snap on a handle at each end, and two workers can easily manipulate the unit into place. Then they just push down and the handles pop off. Before, workers would throw ropes around the unit or try to wrap their arms around it. Handles makes it more contractor-friendly. Second, the design includes grout pockets — two on the bottom of each section, one on each end. These grout pockets are perforated with circular holes and are designed to make it easy to install the laterals level. The contractor puts the unit down on the base grout, taps one end down, and the grout mushrooms up through the holes and locks it in place. So when he goes to the opposite end to tap it down, everything stays put.

wso: Does this design also contribute to filter stability?

Bates: Yes, the grout pockets make the filter more robust and less susceptible to water hammer events. They increase the hold-down strength against internal pressurization of the block. In case of a water hammer condition, the grout pockets help keep the block on the floor even when uplift pressure in that lateral exceeds 30 psi. It’s an extremely robust system that does not rely on mechanical anchors.

wso: What else contributes to the structural integrity of this underdrain?

Bates: On the internal arch of the underdrain are a series of baffles that increase the strength of the block in terms of how much weight can be placed on top. This is perhaps of most interest in desalination pretreatment applications that require a deeper media, but everyone wants a strong underdrain so they can feel confident that it will not crush no matter what they mount on it.

wso: How does this underdrain help optimize filtration performance?

Bates: A dual parallel lateral design ensures uniform backwash air and water distribution, which means a cleaner filter, longer filter runs and lower operating costs. The Type XA underdrain also has dual water recovery channels on the top of the block that help with air distribution during backwash. Across the entire filter, the flow at any point will be within plus or minus 10 percent for air and plus or minus 5 percent for water.

wso: Does this underdrain accommodate different flume configurations?

Bates: It is fully compatible with every flume arrangement, including wall sleeve, center flume, front flume and the Leopold flat-bottom flume.

wso: How does this underdrain work as part of a complete filter system?

Bates: The Type XA underdrain is part of an offering we call the Leopold FilterWorx filtration system. That system also includes the I.M.S. 200 and the I.M.S. 1000 media retainers, which are engineered with precision-molded slots. Another component is the GROUT-TITE bridge, which is placed over the filter flume. It basically creates a solid floor over the flume, so the contractor can pour grout and not worry about any grout falling down inside the flume. Those parts together make up the FilterWorx offering.

wso: What is the ultimate benefit of this system to water utilities?

Bates: It’s a robust filter system that a municipality can put into a plant and not have to worry about, even if the installation technique wasn’t perfect. Even if they have a water hammer event, that filter is going stay in place and produce water day in and day out.


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