Sewer Jetting Pressure and Flows

Water is a powerful cleaning tool. You use high pressure water to clean debris off the sides of pipes, and you use the volume of water or “flow” to flush what was clinging to the side of the pipe downstream. The high pressure water is introduced to the sides of the pipe with a jetting hose capped on the business end with some sort of nozzle, which restricts the flow of the water coming down the hose and allows it to escape the hose via small orifices drilled into the front, sides or rear of the nozzle. These jetting hoses can be as small as ¼” diameter, or as large as an inch or more.

So how much pressure is enough? Well, part of it depends on the pipe size, and part of it depends on the nature of the clog, and part of it depends on the nozzle you are using. Let’s put it this way: 2,000 PSI will peel the paint right off your truck. It’s a LOT of pressure. If you’re in a 4 inch pipe, and your nozzle is running along the bottom of the pipe, you can’t be more than 4 inches away from anything you’re trying to dislodge. 2,000 PSI from 4 inches away is going to knock anything off the sides of the pipe – grease, hair, goo, maybe even little tree roots. But that same 2,000 PSI will be a lot less on the sides and top of the pipe if you’re in an 8 inch pipe.

Here’s where the cost of the jetter comes into play. If the 2,000 PSI jetter is 1/3 the cost of the 4,000 PSI jetter, which should you buy? Again, I’m going to ask, what pipe sizes do you encounter? If everything you do is 4 or 6 inch pipe, the 2,000 PSI jetter is probably the right machine for your needs. If you come up to a larger pipe, you have to understand that you may need to contract that out to another company. If you don’t go much above 8 inch pipe, that 3,000 PSI jetter looks like it will do 90+% of the jobs for you, at half the investment of a 4,000 PSI jetter.

Although there’s a company out there starting to promote 5,000 PSI jetters, remember that bigger is not always better. First of all, operating at 5,000 PSI requires a host of OSHA-mandated specialized protective gear – 5,000 PSI will literally slice right through you if you’re not careful or if your mind wanders at precisely the wrong moment. Plus, if you introduce that amount of pressure into a 4 inch pipe you run the very strong risk that you will tear a clay tile line apart, or even separate the hubs on a run of cast. I don’t even want to think about Orangeburg! That much pressure in the wrong hands might become a very expensive liability if you have to dig up and replace a customer’s drain line.

So when sizing the pressure on your jetter, consider the size of the lines you intend to clean. Then decide whether you want to be able to clean every single line your ever run up against, or if you’re willing to be able to clean only 90% or so, and forgo the other 10% to save your investment cost upfront. There is no right or wrong answer to that question – you have to only you can decide your comfort zone.

Generally hydro-jetters fall into one of three categories: mini-jetters, jetters and flushers. For our use we’ll define a mini-jetter as any jetter flowing 5 GPM (Gallons Per Minute) or less. We’ll define full size jetters as units with self-contained water tanks that flow greater than 5 GPM but less than 30 GPM. And we’ll say sewer flushers flow greater than 30 GPM.

Flow is what clears the pipe of the debris that the pressurized water has dislodged. The HP rating of the engine will determine the amount of force available to push high volumes of water down the pipe to clear debris,as well as the pipe size that can be cleaned.

Electric jetters are limited by their motor size and the available power at the job site. Typically, a 1.5 HP electric motor will deliver between 1.5 and 2.25 GPM, depending on how the manufacturer has the unit configured. A 2 HP motor can deliver even greater pressures and flows, but be careful – the motor weight and size increases exponentially from a 1.5 to a 2 HP unit. What is portable and able to be maneuvered by a single person at the 1.5 HP level quickly becomes a two or more person job when you go to 2 HP and above. These small electric jetters will handle many inside-the-house cleaning tasks, and can even be used in a four inch lateral in the right circumstances.  

But the mini-jetter is limited in pressures, and more importantly it is limited in flow. So if you are tackling a stoppage of any substantive length or hardness, you may need to move up in size. Although 1,500 PSI is plenty of pressure to knock debris from a pipe’s walls, 2.2 GPM will only flush away debris in the smaller household pipes. If you are using an electric jetter on a four inch lateral, it will take you time and patience to correctly and completely clean the line, and even then the flow is questionable to flush away all the debris.

A gas engine mini-jet ups the ante in terms of both pressure and flow. Typically, a 13 HP gasoline motor mounted on a dolly or cart will produce 3,000 PSI @ 4 GPM. The majority of the industry is focused right in this range, though some manufacturers offer units that produce 5.5 GPM, or, with a very small water tank, 8 GPM. We caution you to be very careful with anything above 5 GPM or with an on-board water tank for a couple of reasons. First, you have to feed the jetter and its pump with water. In the U.S., standard hose bibs delivery 5 GPM max, and usually substantially less after accounting for tuberculation in the pipe over time. If you consistently feed a jetter pump with less flow than its designed rate, you will face premature wear.