The following is a story from a contractor who was hired by a city to inspect an 8-inch pipe: When he got there, the city crew had been working for two hours trying to clear roots from the line with their big 65 gpm/2,000 psi jetting truck. The contractor had a 6 gpm/4,000 psi jetter in his van along with his TV system, and the city let him take a crack at the roots. The gpm you will need depends greatly on the pipe diameter being cleaned and whether or not you really are required to flush/scour the line clean, or if you just need to penetrate a blockage to restore flow. This is also why little 2 gpm electric jetters don’t flush out much debris. This is why city and county crews clean 8- to 12-inch pipe with 40 to 60 gpm, and larger pipelines with 80-plus gpm trucks. If you want to move larger rock, bricks, grease-logs, etc., you’ll need more gpm. “Wider” waterjet streams shooting out of a jetting nozzle will have the most “flushing” action, and more volume also means more impact in the cleaning. If the gpm is adequate, the sheer volume of water will push and carry debris. Experience has shown that a 3,500 to 4,000 psi jetter with 6 or more gpm and the right nozzle or tool will cut out root masses, chop up hard grease, and carve out hard settled dirt. We’ve shipped dozens of jetters that do 9 gpm/4,000 psi for cutting out this kind of crud from 3- to 8-inch drains and sewers. Pressure cuts are also why 4,000 psi trailer-mounted jetters at 18 gpm are so common with contractors who get paid to cut out blockages. This is also why the little 1,500 psi electric-powered units don’t cut out much at all. “Thinner,” high-pressure waterjet streams from a good jetting nozzle will have the most “cutting” power if the psi is adequate. When choosing a jetter’s output in psi and gpm, remember this hydrojetting rule: Pressure (psi) is “cutting” power, while gallons per minute is “flushing” power. I’ve learned a lot since then, and the most common question I get asked is: “When choosing a jetter, what is more important: gpm or psi?” Back then I didn’t really know what a jetter was, I just had a set of specs. I designed and built our first jetter 20 years ago a little 3.5 gpm/4,000 psi portable unit. Get Plumbing articles, news and videos right in your inbox! Sign up now.
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