Orthos Bore Sizes

What is a Filter Nozzle? Part ​III

Proper Pressure Drop Design

As the leader in the nozzle-based filter systems and products, Orthos has by far more injection molding capabilities and over a million filter nozzle design combinations in order to provide the correct solution for your application.  R&D performed in our Orthos Research Center evolves new and improved nozzle products, while others still plug-and-chug mid-20th century legacy products in a one-size fits all manner.

How do we know how to select the correct nozzle product for your application?

This video is part three of a four-part series regarding filter nozzle/strainer construction.  Here, I will discuss Proper Pressure Drop Design of nozzles in monolithic or steel plate underdrains.

To watch Parts 1 and 2 of Filter Nozzle Construction click below:

Appropriate amounts of pressure drop or head loss through the nozzle at operating flow rate ranges is important to ensure proper distribution during backwash.  Enough pressure drop through the underdrain is required to overcome the head loss of the dirty media bed.  Otherwise, uneven distribution occurs, allowing unwanted channeling and poor media cleaning, which reduces subsequent filter run times and creates maintenance issues due to the left-over solids.  For typical sand/anthracite/GAC applications, Orthos recommends at least 20 to 25 inches of Water Column at the design high backwash rate.  Please contact Orthos for each application, especially involving specialty media and atypical filter operational strategies.

Screen Construction

36 slots .3 mm Filter Nozzle Screen

36 Slots, 0.3 mm Slot Width

36 .2mm Slot Filter Nozzle Screen

36 Slots, 0.2 mm Slot Width

Filter nozzle with 24 slots .2mm width

24 Slots, 0.3 mm Slot Width

There are two main design elements that determine pressure drop through a nozzle at a given flowrate. First is screen construction. Be sure to watch Part One of this series in which I discuss screen slot width. A choice may be required between more than one appropriate width.  For the same number of slots, smaller width slots impart more pressure drop than larger.  Utilizing the same width slot, fewer slots in a screen will create more pressure drop at the same flowrate.

Bore Size

Orthos Bore Sizes

The second design element is the bore size of the thread section and the tailpipe, if used.  Orthos commonly selects amongst four constructions, though more are available.  In increasing pressure drop for a given flow rate, bore diameters of 21mm, 16mm, 16mm with a 13mm restriction in the thread section, and also 13mm may be utilized.  To add even more pressure drop, a closed stem with holes may be used—7 hole sizes are available.

ORTHOS engineering staff will select the correct nozzle construction combination to optimize performance for your specific application.  Proper nozzle characteristics ensure media retention, negate fouling, and produce excellent distribution, which all will deliver optimal filter performance.

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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.


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