What is a Filter Nozzle? Part II


Filter Nozzle Geometries and Mounting Methods

Nozzle Geometry

Nozzle geometries are typically either cylindrical or somewhat conical. Our injection molded nozzles utilize v-shaped, vertical slots that prevent fouling.  Some believe that the older-style conical nozzles have an angular backwashing benefit; however, cylindrical nozzles are manufactured with robust, reinforcing screen ribs that ensure added longevity.

The size of a nozzle is directly proportional to flowrate. Look at both the service as well as backwash rates to determine the controlling design conditions.  Comparing some non-lateral nozzle models with the same screen slot size and stem bore diameter, the flowrate capacity for a Type K3 is higher than Types K2 and C2, which in turn are higher than Types K1 and C1, which have a higher capacity than a Type D.  

Nozzle density in the underdrain system factors into the flowrate per nozzle.  For example, for the same gpm per square foot backwash rate, designing nozzles on 8” centers each way requires 78% more flow per nozzle than designing nozzles on 6” centers each way.  Orthos highly recommends nozzles to be located as close as practicable to ensure effective media cleaning through more points of energy input and to potentially eliminate gravel and other types of problematic packing layers.

Mounting Methods

Filter Nozzle

Mounting methods of non-lateral nozzles depend on the underdrain type.  For monolithic, reinforced concrete underdrains such as the Orthos Centurion™, nozzles thread into concrete sleeves that are cast into the floor.  Non-tapered threads, such as the 1” NPS used by General Filter (now WesTech), require Orthos to supply an o-ring to lock our replacement nozzle into place.

Four options for steel plate underdrains: (All require a gasket for air scour applications)

      1. First and the most time consuming, holes drilled in the plate are tapped and nozzles threaded into the holes.

      2. Second, plate holes may be drilled, nozzles inserted, and a backup nut threaded on from the underside which must be accessible.

      3. Third, a Type MUZ locking nut and washer will permanently secure a nozzle from the underside.

      4. Fourth and usually Orthos’ recommendation, is to use an expanding ring.  The gasket is mounted onto the expanding ring and placed into the hole location. As the nozzle is threaded into the expanding ring, its legs secure the nozzle in place like a toggle bolt. These components may all be easily installed from the top side of the underdrain plate.

Nozzles for pipe header-laterals may be mounted directly using a pipe saddle and expanding ring.  For header-lateral systems embedded in concrete, pipe sleeves with temporary caps may be glued onto PVC or CPVC pipe.  After the concrete has been poured and cured, the caps may be removed and nozzles installed.  Alternatively, a bottom-threaded concrete sleeve with temporary cap may be threaded into an expanding ring with pipe saddle.

Orthos has numerous configurations of hub and lateral systems as well as lateral nozzle systems that replace pipe laterals and mount directly onto the header.  Please contact us for proper mounting and configuration of these type systems.

If you missed Part 1 of this series, click here. I thoroughly explain how to select proper nozzle material and screen slot width.  In Parts 3 &  4, I’ll discuss nozzle pressure drop design and nozzle tailpipe construction for air scour applications.


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Remember Orthos’ HUGE life cycle cost benefits– At the end of the filter’s life cycle (~25 years), in contrast to a complete plastic block or folded sheet metal underdrain overhaul, nozzles are simply replaced
potentially saving $Millions.