Author: Steve JONESIE Jones
I designed and built our first jetter 20 years ago, a little 3.5gpm/4000psi portable unit. Back then I didn’t really know what a jetter was; I just had a set of specs. 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(flow) or PSI(pressure)?” Consider this…
When choosing a jetter’s output in GPM & PSI, remember this hydro jetting rule:
PRESSURE (PSI) is “CUTTING” power, while GPM (Gallons Per Minute) is “FLUSHING” power
Pressure Cuts into blockages:
“Thinner” high-pressure waterjet streams from a good jetting nozzle will have the most ‘cutting’ power if the PSI is adequate; experience has shown that a 3500-4000psi jetter with 6 or more GPM and the right Warthog nozzle/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/4000psi for cutting out this kind of crud from 3″-8” drains and sewers. Pressure cuts is also why 4000psi trailer-mounted jetters at 18-gpm are so common with contractors who get paid to cut out blockages. This is also why the little 1500psi electric-powered units don’t cut out much at all.
GPM (‘Volume’) flushes out debris:
“Wider” waterjet streams shooting out of a jetting nozzle will have the most ‘flushing’ action, and more volume is also more impact in the cleaning. If the GPM is adequate the sheer volume of water will push and carry debris. If you want to move larger rock/bricks/grease-logs, etc., you’ll need more GPM. This is why City & County crews clean 8-12” pipe with 40-60gpm, and larger pipelines with 80+gpm trucks. This is also why little 2gpm electric-jetters don’t flush out much debris. 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.
Example story from the field:
A story from a contractor that was hired by a City to video-inspect an 8” pipe: When he got there, the City crew had been working for 2 hours trying to clear roots from the line with their big 65gpm/2000psi jetting truck. The contractor had a 6-gpm/4000psi jetter in his van along with his TV System and the City let him take a crack at the roots. Using a “Warthog” Slow-Rotating Cutter-Nozzle, the contractor cleared the roots and then finished the video inspection. Notice that he got done with a 20-horsepower unit what the City could not do with a 100-horsepower unit. Why? Because (a) he had the right tools and (b) PRESSURE CUTS. The contractor said in the article “you should have seen their faces!” In contrast, it is important to also realize that if we were talking about clearing rocks and debris (instead of cutting roots) then the story would be the opposite; the 65-gpm truck would run circles around the 6-gpm jetter, because VOLUME FLUSHES.
Note: using the right nozzle/tool also makes a huge impact; choose “the right tool (nozzle) for the job”
The ‘GPM-to-pipe-diameter ratio’ is another good rule of thumb in choosing minimum jetter GPM:
The GPM of the jetter & nozzle should be at least equal to the diameter in inches of the largest pipe you clean, and the best cleaning is a 2/1 ratio (i.e. 8gpm/4″ pipe). Therefore it is wise to consider before choosing a jetter; (a) what are the most common pipe-sizes that your jetter will need to clean, and (b) what will the jetter’s primary job be for you (flush debris/rocks/dirt etc., or cut out grease/roots, etc.)?
Most contractors are in the job of re-establishing flow in drains and side-sewers; you can break through blockage in 4” & smaller pipe with less than 6gpm, while the 8gpm to 18gpm machines will do a better job of cleaning and are much better in 6-18” pipe. Again, choose GPM based on what size pipe you most commonly deal with. Also, understand that a jetter’s GPM is always listed at maximum throttle, so if the engine speed is reduced then the GPM reduces therefore if you can afford a higher-GPM jetter then you can also “slow it down” for use in smaller ID pipe. The pressure will be maintained if you also have nozzles sized for the lower GPM in addition to your standard full-GPM nozzles. It also works great to do this with a smaller-diameter “mini” jet-hose, a very common & profitable practice among high-flow jetter operators.
Hope this was helpful — get jetting!Steve JONESIE Jones Sales Director Jetters Northwest firstname.lastname@example.org (877) 901-1936