When you're picking out a jetter, one of the first questions you'll run into is: should I prioritize PSI or GPM? Flow or Pressure? It's a fair question, and one that trips up both first-time buyers and seasoned pros. The truth is, GPM & PSI each serve a different purpose in the jetting game, yet it takes both to create cleaning-power. In this breakdown, we’ll dive into the real-world performance of both pressure and flow, how they work together, and which setups deliver the best water-jets for attacking various blockages & buildup in the pipe.

GPM (Water Volume) Impacts & Flushes:

The more GPM (Gallons Per Minute) a jetter produces, the “larger” its waterjet streams will be as they shoot out of its jetting nozzle. Larger waterjets have more volume thus more impact in the cleaning, as well as more ‘flushing’ action. Think of the size of a claw-hammer versus a sledgehammer - the more massive one will obviously have more impact. It’s the same with GPM. If the GPM is adequate the sheer volume of water will punch through blockages, then carry away the 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 have the impact to attack tough blockages and struggle to flush out debris. For service-jetting, 8+ GPM, on up to 20 GPM, is plenty to do “Rooter-Class” cleaning. The GPM you will need depends greatly on the pipe-diameters you’ll most typically clean - we will unpack that later in this blog. Another factor is whether or not you really are required to flush/scour the line clean, versus simply clearing a blockage to restore flow.

PSI (Water Velocity) Penetrates & Cuts:

As you read a jetter’s pressure gauge, what it really tells you about is the speed of the water-jets as they shoot out of the cleaning-nozzle. Literally, 3500psi water-jets are moving faster than 2500psi water-jets. The whole reason we build pressure in a jetting system is to force the water to speed up in order to escape the nozzle and hit the blockage or buildup to be cleared. And the faster the water-jets are moving the more penetrating and cutting action they can offer us. However, remember that it takes GPM of water to do cleaning. And if we think of GPM as the “size” of our jetting “hammer”, then think of PSI as an indication of how fast we can swing that hammer at a blockage or buildup in the pipe. The high-pressure waterjet streams from a premium jetting nozzle will have ‘cutting’ power if the GPM & PSI is adequate, and experience has shown that a 3000-4000psi jetter with 8 or more GPM - and the right nozzle/tool - will indeed cut out root masses, chop up solidified grease, carve out hardened buildup, etc. We’ve shipped hundreds of Jetters that do 9-gpm/4000psi for cutting out this kind of crud from 3″-8” drains and sewers. Pressure cuts is why 3000-4000psi jetters are so common with contractors who get paid to cut out tree-roots and tough blockages. This is also why small 1500-2000psi electric-powered jetters are only used for softer blockages like sludge and soft grease; they simply lack the water velocity & volume to impact & clear the tough stuff.

PSI vs. GPM: Side-by-Side Comparison

Feature	PSI (Pressure)	GPM (Flow)
Main Role	Velocity for Impact & Cutting Power	Volume for Impact & Flushing Power
Best For	Carving out tree-roots, hard grease, compacted silt, etc.	Impacting blockages, flushing debris, scouring the pipe-wall
Example Use	3000-4000 PSI for jetting 3”–8″ pipe	8 GPM up to 20 GPM for clearing 3”–18″ lines
Common Units	8–13 GPM at 3000–4000 PSI, typically as a Van-mount jetter, Portable-Cart, or Trailer	14-20 GPM at 3000-4000 PSI, typically as a larger Trailer jetter or larger Skid-mount for box-truck or flatbed

Real-World Example: Pressure vs. Flow in Action

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 4000psi jetter in his van along with his TV System and the City let him take a crack at the roots. Running less than 10gpm and using a “Warthog” Slow-Rotating Cutter-Nozzle, the contractor cleared the roots in minutes, and then finished the video inspection that he was hired to do. The contractor said in the article “you should have seen their faces!” Notice that he got done with a jetter under 30-horsepower what the City could not do with a 100+ horsepower unit. How? Because:

• Pressure Cuts
• He had the right jetter & nozzle for the job

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 contractor’s Van-Pack jetter, because volume flushes. PRO TIP: Using the right nozzle/tool for the job has a huge impact on a jetter’s cleaning action; basic “penetrator” nozzles are not “root-cutting” nozzles - choose the right nozzle for the job. 

How Pipe Size Should Guide Your GPM Choice

It is wise to consider before choosing a jetter:

• What are the most common pipe-sizes that your jetter will need to clean?
• What will the jetter’s primary job be for you? Clear soft clogs/sludge? Cut out tree roots/ hard grease/etc.? Flush debris/rocks/dirt etc.?
• Will you primarily do quick clog-busting jobs, or jet longer pipelines requiring complete scouring & flushing?

Most contractors are in the job of re-establishing flow in drains and side-sewers. For clearing simple “soft clogs” the jetter’s GPM should be at least equal to the diameter in inches of the pipe to be cleaned (e.g.4gpm for 4” pipe), BUT for “Rooter-Class” jetting we recommend a 2-to-1 ratio of GPM-to-Pipe Diameter, such as 8+gpm jetter for clearing 4″ pipe, 12+gpm for 6” pipe, etc. You can break through soft clogs in 4” & smaller pipe with only a few GPM, but higher-flow jetters that put out 8+gpm, on up to 20gpm, will do a much better job of clearing blockages & buildup  from 4”-12” service lines without spending all day on the job. Again, choose GPM based on the pipe-sizes you’ll most commonly be jetting, and whether you’ll do spot-work or entire pipe-runs. If you were to mow sports-fields for a living you probably wouldn’t settle for a push-mower, right?  To get jetting jobs done in a timely manner don’t settle for a jetter with too little GPM! Also, understand that a jetter’s GPM is always listed at maximum throttle, so if the engine speed is reduced then the GPM reduces as well, therefore if you can afford a higher-GPM jetter then you can also “slow it down” to save fuel, reduce engine-noise, AND to lower the GPM-flow when jetting smaller-diameter indoor lines. The PSI will be maintained if you have smaller nozzles that are sized for the lower GPM in addition to your standard full-GPM nozzles. Those smaller nozzles pair up nicely with smaller-diameter “mini” jetting-hoses for jetting those smaller indoor lines; a very common and profitable practice among “rooter-class” jetter operators. Hope this was helpful — “get jetting”!

Looking for the Right Jetter Setup?

At Jetters Northwest, our goal is simple: equip you with the right jetting tools and knowledge for the job. Every drain line brings a different challenge, which is why we build jetters with GPM/PSI options for cutting, flushing, or striking the balance between both. Explore proven setups like Brute Van-Pack & Cart jetters for everyday residential and light commercial lines, or Eagle Trailer jetter for bigger jobs and long runs, and handy Mini-Jetters for jetting small indoor pipes. Not sure which setup fits best? Give us a call. We’ll walk through your jobs with you and point you toward the jetter package that makes the most sense; no pressure, just practical advice from the shop floor.

Pro-Insight from the Shop Floor: Steve JONESIE Jones

“I designed and built our first jetter over 30 years ago, a little 3.5gpm/4000psi portable unit for a plumber. Back then I didn’t really know what a jetter was; I just had a set of specs and a few years experience servicing high-pressure cleaning systems. I’ve learned a lot about the sewer & drain world since then! That small 3.5gpm jetter I built was fine for the plumber to clear “soft-clogs”, but I learned quickly that a “rooter pro” wants 2 or 3 times that GPM to attack serious sewer/drain problems. Therefore, when choosing a jetter’s output in GPM & PSI, remember these hydro jetting rules-of-thumb:

• PRESSURE (PSI) is “CUTTING” power
• GPM (Gallons Per Minute) is “FLUSHING” power
• The COMBINATION of GPM & PSI provides hydro-jetting IMPACT 

Thus, a Jetter’s GPM & PSI specs together define its CLEANING Power-Potential! We’ve designed and sold literally thousands of jetters over the last 30+ years, with flows from under 2-GPM on up to 20+GPM and all points in-between.  We very much appreciate the wonderful feedback and good advice from the great contractors and jetting pros across the nation and around the world that have supported us on the journey!”