TECHNICAL 43
Retro cutter with spinning head nozzle – drain and sewer ( cutting of roots and debris ).
• Sewers vary in diameter and have different degrees of blocking . For normal domestic sewers , a 30 l / min pump at 150 to 200 bars will suffice . The nozzles required are simple mini bombs with forward and rear facing jets . Main ’ s sewers are of a large diameter ( up to 300mm but usually about 200mm ) and these require a minimum of 80 l / min at 150 to 200 bars . A 120 l / min pump helps to pull the hose better , especially where the sewer has a long space between manholes . Cutter nozzles , chain flail nozzles and bomb nozzles are all used in this application .
• Rainwater and storm water drains require much larger pumps . They usually need 150 to 200l / min at 150 to 200 bars . Bomb nozzles can be used , but where sand is the main problem , the ‘ flounder ’ nozzle is the most effective . This nozzle consists of a block of metal with a pointed front and usually four rear facing nozzles . When the nozzles reach sand , they tend to ride up and over it and in doing so , cause the rear jets to agitate and fluidise the sand . The large volume of water carries the sand back to the manhole where it is removed , either physically , or by means of a jet pump which only uses a small portion of the pump flow to push the sand out . PA
Bomb nozzles drain and sewer .
Small bomb nozzle .
“ They need special nozzles designed for each specific application .”
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July 2021 Volume 27 I Number 5 www . plumbingafrica . co . za