When setting up cleaning and maintenance programs for sewers and other underground assets, public works directors and network operators tend to focus on jetting trucks. And naturally so; jetters and jetting trucks are essential components are absolutely essential equipment for any maintenance department. And, they’re expensive — at up to $300,000 or even more, jetting trucks typically represent the most expensive asset in a maintenance department’s inventory.
But paying attention to the acquisition and use of sewer nozzles — a relatively inexpensive piece of equipment — is also incredibly important for efficient and cost-effective sewer cleaning.
For one thing, the proper use of high-quality sewer nozzles is the best way to get the best and most efficient performance from jetting equipment, and from sewer cleaning crews. It’s also the best way to get the most performance out of expensive jetters —using good nozzles at the optimum pressure extends the lifespan of expensive jetters, effectively providing an enormous return on investment. And most importantly, good nozzles used properly also improve the performance and extend the lifespan of sewers. For these reasons, making time to evaluate and acquire excellent sewer nozzles, and implement training and workflows for optimum use, may well be, hour-for-hour, the very best investment of time and focus that sewer network operators can make.
What Is ‘Optimum’ Pressure?
Intuitively, it would seem that more pressure is always better when considering jetting equipment and sewer cleaning. This is certainly a view encouraged by the equipment makers, who routinely promise 4,000 psi or more — enough to ‘peel the paint’ off a truck (or cut it in half).
But the seemingly obvious conclusion that more pressure always equals more efficient cleaning is wrong, even dangerous. Josh Ballum, Nozzteq’s technical support manager — who has visited thousands of sewer-cleaning crews in the field, and who performs hundreds of sewer nozzle demonstrations annually — says that with a good nozzle, you don’t need full pressure. In fact, it’s usually counterproductive.
“I like to run our nozzles on the customer’s equipment, running just above idle, and then compare it to the nozzles they’ve been using, with the psi cranked way up. There’s no comparison; I’ve never lost,” he says, “Even at the lowest possible truck pressures, NozzTeq’s jetting nozzles produce a far more powerful jet stream.”
In fact, extensive laboratory and field testing by NozzTeq technicians has proven that nozzles work most efficiently at no more than 950 psi — far less pressure than jetting equipment vendors typically recommend. But note, this is the optimum jetting pressure when measured at the nozzle end of the hose. That is, the pressure of water emerging from the truck is relatively unimportant; the critical factor is actually the pressure being produced at the nozzle end of the hose, and this pressure is always significantly reduced from truck end pressure, depending on the length of the hose used.
Therefore, jetting crews should always be familiar with the functional jetting pressure being produced at the nozzle end — the ‘business end’ — of the hose being used. And, they should be able to precisely calibrate this pressure as needed for the best use of particular nozzles. There are several ways to develop this vital knowledge:
- Routine use of inexpensive testing mechanisms that can be attached to the end of the hose.
- Routine use of formulas and tables that calculate available nozzle-end pressure as a function of pump psi, pump gpm and hose length. These should be available from your nozzle vendor (NozzTeq provides them on request) and are easy to use.
- Your nozzle vendor should be able to do a hose-end nozzle test for you during a field visit. This is a service that NozzTeq representatives routinely provide, hundreds of times a year.
Routinely operating jetting trucks and jetting equipment at lower pressures is, in itself, a big efficiency and cost-effectiveness gain for sewer networks. Lower pressure means less fuel used during jetting, far less wear and tear on equipment (which extends equipment lifespan and reduces maintenance costs), less wear and tear on sewers (since they are subjected to less pressure when cleaned), and reduced labor costs (since crews clean more sewer more quickly). Using lower pressures when jetting is the very definition of a win-win proposition in sewer maintenance.
And it’s also important to note that if the pressures generated by most jetting equipment are considerably higher than needed for efficient sewer cleaning with high-quality nozzles, then it may be possible for network operators to get excellent results with reduced initial investments in jetting equipment.
“Companies and municipalities invest hundreds of thousands of dollars on their jetting trucks and crews, and then they spend $50 on a nozzle. It doesn’t make any sense,” says Ballum, “A good nozzle can make a mediocre truck look good…and vice-versa. To get the most out of any investment in a sewer jetter, you have to get the right nozzle.”
But, what exactly is the “right nozzle?” Put another way, what are the sewer nozzle design and construction features that DPWs and sewer network operators should look for in order to get maximum efficiency and performance from expensive jetting equipment?
Why Are Some Sewer Nozzles Better?
High-quality sewer nozzles, such as those developed and distributed by NozzTeq, are better for cleaning sewers for one important reason—they take maximum advantage of jetting pressure by preserving laminar flow and smooth powerful jetstreams from truck to nozzle.
“Laminar flow” is a fancy term for a concept we’re all quite familiar with; laminar flow is the opposite of turbulent flow, and we see both all the time in kitchen sinks when the initial smooth, focused laminar flow from a faucet is overwhelmed and made turbulent as the faucet is opened all the way and water particles cease moving in parallel and the flow becomes turbulent. When filling a sink or washing one’s hands, turbulent flow is fine — you’re only concerned with the quantity of water emerging. But when cleaning sewers, turbulent flow is disastrous. Turbulent flow means that the stream of water emerging from a nozzle is dispersed into ineffective spray, rather than emerging as a tight, focused jetstream that powerfully dislodges debris and grease and moves it quickly downstream and out of the pipe.
Preserving laminar flow from truck to jetstream is the only way to produce the effective jetstreams that give jetting equipment its name.
Two factors affect laminar flow: pressure, and internal nozzle design. Too much pressure creates turbulent flow just as it does in faucets. And badly designed nozzles with, for example, D-shaped internal conduits or simple drilled orifices, also inevitably create turbulence due to poor hydrodynamic performance. And network operators can’t simply overcome poor nozzle design by using higher pressures; higher pressures actually make things worse, because they create more turbulence and further degrade jetstreams. As Ballum says, “Instead, the flows break up and become turbulent which dissipates power… no matter how high you crank truck pressure.”
By contrast, well-designed sewer nozzles, such as those that meet Tier 3 standards established in the NASSCO Jetter Code of Practices incorporate smooth internal conduits, precisely shaped orifices, and other features that preserve laminar flow and focus optimally pressurized water into the tight, powerful jetstreams that actually clean sewers effectively and efficiently.
For sewer maintenance departments, this all adds up to a couple of simple principles that will help you clean more sewer more efficiently and more cost-effectively.
- Take the time to understand optimum water pressure — at the nozzle end — for sewer cleaning.
- Buy high-quality nozzles. It’s a modest investment that will repay itself many times over, reducing your bottom line while also extending the lifespan of your costly underground assets and jetting equipment.