What filter nozzles do
Filter nozzles (also called strainers) are the small slotted components fitted to the underdrain plate or laterals of pressure filters, softeners and DM plant vessels. They do two jobs: hold the media bed in place while letting filtered water pass, and distribute backwash water and air evenly across the bed.
A filter with even a few broken nozzles suffers media loss into the treated water line, channelling during backwash, and steadily worsening filtrate quality.
Common nozzle designs
Different vessels use different designs, including push type nozzles that press into the plate, threaded types (BSP threads are common in Indian plants), umbrella type for plate collection systems, double decker designs for combined air-water backwash, ring type and dome/bowl strainers, bolt-fixed types for header-lateral systems, and dedicated cooling tower nozzles. Browse the designs Bluestone supplies on the nozzles & strainers page.
The three things to get right
Slot size. Slots must be narrower than the finest media resting on the plate. For fine filter sand, typical slot widths are a fraction of a millimetre — measure the media, not the old nozzle, if media has been changing over the years.
Fixing and thread. Confirm the fixing method (push, screw, bolt) and thread size against the plate. Sending a photograph and a sample of the old nozzle is the most reliable way to get an exact match.
Flow rating. The combined open area of all nozzles must pass service flow and backwash flow without excessive pressure drop. When re-nozzling a full plate, keep the count and rating consistent with the original design.
Replacing nozzles: sample-first ordering
The safest workflow when a filter is opened for inspection: photograph the plate, count the nozzles, keep one intact sample of each type, and share these with your supplier. Custom sizes and shapes can be produced for non-standard vessels — allow lead time for these when planning a shutdown.