Municipalities responsible to keep sewer lines free from debris and blockages face the challenge of maintaining these lines during a time of rising fuel prices and water scarcity throughout much of the United States.
To reduce costs and conserve these resources, cleaning crews must adopt more efficient cleaning equipment, tools, and techniques to implement water-intensive cleaning that can involve a hundred gallons of water per minute. Fuel is also consumed to operate the sewer truck, vacuum system, water pump, operating platform, and pressure/flow compensation hydraulic system.
Fortunately, using more effective tools and methods can cut the industry’s fuel and water usage. Inefficient sewer cleaning nozzles and poor cleaning techniques can cause crews to make many passes to clear a line. But this wastes fuel and water. When crews inefficiently use water, additional fuel, time, and labor are required to drive to the nearest fire hydrant to refill the tank.
Dan Story, a trainer and operations manager at KEG Technologies, a manufacturer of sewer and storm line products, says crews must pay attention to water conservation or they can’t do their jobs. Story says that with high fuel prices and a scarce water supply, municipalities look to stretch their resources with better training and tools.
INCREASING EFFICIENCY
To clean sewer lines more efficiently, municipalities should consider using more effective tools and methods. Normally, sewer crews use jetting and/or vacuuming systems to remove debris and blockages.
With jetting, an operator places a high-pressure water hose with a high-performance nozzle into the line. Operators release high-pressure water from the sewer jet truck to dislodge debris and flush it into a manhole. As debris is removed, the hose is pushed deeper into the sewer. Jetting typically involves using between 50 to 85 gallons of water per minute to flush out debris lodged in the pipe. A vacuum may also be used to remove dislodged debris and transfer it to disposal bins.
HIGH EFFICIENCY TOOLS
One of the most effective ways to decrease water and fuel use while improving cleaning efficiency of sewer vacuum trucks is by using a high-performance, Tier 3 nozzle. With improved fluid dynamics, these optimize the cleaning process while using less water, revolutions per minute (RPMs), and pressure (PSI). These nozzles cost more, but reduce fuel and water costs and enable faster cleaning.
Nozzles are classified in three efficiency-based tiers: Tier 1 (approximately 30% efficient), Tier 2 (50 to 60% efficient), and Tier 3 (75 to 98% efficient). According to Story, however, a surprising number of municipalities and third-party contractors still do not use Tier 3 nozzles for sewer cleaning, despite the benefits.
What sets the Tier 3 nozzles apart is the fluid mechanics engineering on a par with the aerodynamics of race cars. After exiting the jetter hose, water travels into the body of the nozzle before moving through smooth, curved channels. This design enables the water to maintain its power and speed before entering the nozzle’s replaceable titanium ceramic inserts, which help straighten the water stream. Next, the water is further funneled to enable an even tighter water pattern to emerge.
The internal workings of the nozzle redirect the energy of the high-pressure water entering the nozzle so it performs as efficiently as possible. This results in more thrust and power using less water.
“If there is turbulence in the water as it exits the nozzle, it dramatically reduces the overall cleaning power,” Story says. “The most effective Tier 3 nozzles create tight water patterns that efficiently clean the pipe wall and produce a powerful water stream to move debris long distances while propelling the nozzle through the lines.”
TIER 3 EFFICIENCY
In the case of KEG’s Tier 3 nozzles, such as the Torpedo and OMG models, the high-performance design of the fluid mechanics leaves little room for power losses and excessive turbulence; therefore it can achieve 98% efficiency. A properly designed Tier 3 nozzle can also be used at lower operating pressure (PSI) and RPMs.
Story explains that when water hits the nozzle wall of Tier 1 and 2 nozzles, they stop the flow of water and change its direction. In contrast, Tier 3 nozzles are designed not to impede or stop the water flow. The result essentially eliminates water turbulence and produces a much more powerful flow of water directed from the nozzle.
According to Story, a Tier 1, 30-degree drilled nozzle running 72 gallons a minute at 2,200 PSI will only exert 13 lbs of force to move debris nine feet away from the nozzle. But a high-efficiency Tier-3 nozzle running 60 gallons a minute at 2,000 PSI will exert 98 lbs of force nine feet away.
He adds that efficient Tier 3 nozzles also allow a lower water pressure to be used from the truck, which saves water.
“If you lower the pressure, you lower the gallons of water being used per minute,” Story says. “This results in water savings. With the Tier 3 nozzles, you can lower the required water pressure in PSI without compromising power.”
CLEANING SPEEDS
Superior cleaning techniques can also reduce fuel, time, and labor. According to Story, the main mistake most operators make is when they do not understand how their cleaning speed affects their performance.
“The hardest thing to overcome is that for years operators were taught to quickly spray water on the way up the sewer line and then clean as they return,” he says. “But that wastes water because it does not move the debris or clean the walls sufficiently.”
With poor techniques, operators are often forced to make several passes to remove the material, wasting water. “Even after that, I have been in situations where after a cleaning the CCTV camera operator radios back to ask if the line was even cleaned,” Story shares.
“Most operators want to run up the line in a hurry and clean as they come back because it is how they were taught, but it is impossible to ‘dig a hole from the bottom up,’” Story explains. “When they shoot past all the debris going in, they are trying to bring it all out at once, which is more difficult.”
Instead, Story advises operators to go slow when cleaning lines.
“You want to go in slow, between 30 ft and 60 ft per minute,” Story says. “Remember, at 60 ft per minute, you are traveling one foot per second. However, at one foot a second, you are wetting the pipe, not cleaning it.”
CLEANING EFFICIENTLY
Story advises operators to pull the nozzle down as they go into a line, observe how dirty it is, and then adjust their cleaning speed accordingly.
“If you are not getting a lot of debris back in the first 50 ft, then you can increase your cleaning speed,” Story says.
When the operator reaches a manhole in the line, he advises dialing down the water pressure to 900 to 1,000 PSI as they return.
“You clean the line, remove all the organic materials going in, and some of the rocks in it will fall out of the flow,” Story says. “By cleaning as you go in, however, you’re able to get the dirt and debris out of the line, so on the return the rocks will move much easier inside the pipe.”
He states that operators often compensate for a lack of power cleaning with Tier 1 or 2 nozzles by increasing the pressure and the water flow. However, with a Tier 3 nozzle, a lower pressure is possible.
“A Tier 3 nozzle can generate the same amount of cleaning power as a Tier 1 or 2 using 40 gallons and 1,200 PSI, saving time, water, and fuel,” Story says. “But the trick to that is cleaning as you go in. Chop the debris up, and let the flow work like a conveyor belt, carrying the debris out. If you clean correctly, the water is going to carry the debris off. When you get to the end of the line, just dial your pressure back down and rinse the pipe as you come out. When you come back, the job is done. You don’t have to send it back in a second time.”
SAVE TIME & WATER
With 6- to 15-inch diameter sewer lines, it should be possible 95% of the time to go from manhole to manhole and clean in a single pass, Story says. “This takes a fraction of the time and resources to make one pass versus making several passes to remove the same material.”
It also eliminates extra trips to a nearby fire hydrant to refill the water tank, which can cost crews an hour or more to put all equipment back on the truck and set it up again when they return. With a combination of the right tools and techniques, Story estimates that sewer crews can save approximately 9 to 17% in vehicle fuel costs, including travel to refill water tanks.
As municipalities and contractors seek to reduce the use of costly fuel and scarce water, using the most efficient Tier 3 nozzles and cleaning methods will go a long way to stretch their funds and conserve valuable resources. Just as important, adopting industry-proven cleaning techniques will help to protect against future increases in the cost of fuel and water.
ABOUT THE AUTHOR
Del Williams is a technical writer who lives in Torrance, California. Find out more about KEG and water, fuel, and time savings, visit www.kegtechnologies.net.
