Many municipalities — large and small — are faced with a daunting challenge. The sewer infrastructure winding under these communities is rapidly showing its age and funding to rehabilitate these lines is limited at best. Maintaining proper flow within sewer lines is becoming ever more critical.
Numerous things can restrict flow in sewer pipes. These may include tree roots, minerals, dirt, grease, sludge and damaged pipes. Depending on the size of the community, it may have a department that specializes in cleaning sewer pipes. However, in many cases this work is subcontracted.
Sewer jetting is an effective method to remove debris from sewer pipes ranging from 4 to 72 in. in diameter. The sewer-jetting process is quite simple — high-pressure water is introduced into the sewer pipe via a hose equipped with a specially-designed jetter nozzle that directs water forward and also to the sides of the pipe. The jetter nozzle can produce up to 5,000 psi and blast away debris within the pipe.
The water pressure will pull the nozzle and hose through the pipe. The idea is to always work uphill, so as you are cleaning the debris out, it is flushing down the pipe. As the debris flows downhill, it is removed from the pipe with a hydro excavation vacuum.
There are a number of different types of sewer-jetting systems available. Some systems are dedicated units that focus only on the sewer-jetter cleaning function and require a separate vacuum unit to remove the debris from the sewer line. Other systems combine the vacuum and sewer-jetter functions into one unit. There are also trailer- and truck-mounted units. Truck-mounted units typically are designed to clean large-diameter pipes while trailer-mounted systems are ideal for sewer pipes up to 20 in. in diameter.
While truck-mounted units have been the norm, contractors and municipalities are turning to trailer-mounted systems for a couple of reasons.
“The main reason for the shift is that trailer systems are very effective in cleaning sewer pipes up to 20 in. in diameter and at a lower cost compared to using the larger truck systems,” says Mike Moore, vice president of sales for McLaughlin. “This allows the municipality to expand their coverage and dedicate the more powerful truck system on the larger and more difficult sewer-jetting projects. Most trailer-mounted systems begin as a hydro excavation vacuum and then a sewer-jetter system is added to the unit.”
The City of Oldsmar, Fla., did just that. The water department purchased a trailer-mounted system and the deciding factor over a truck-mounted unit was cost and maneuverability.
“We purchased a 500-gal, trailer-mounted unit for storm-drain maintenance,” says John Derry with the City of Oldsmar. “Cost was the main driver in selecting a trailer-mounted unit. We needed another unit and couldn’t warrant the cost for a truck-mounted system. The trailer system gives us everything we need in a small package. In addition, the trailer system is easier to get into hard-to-reach projects and more cost-effective to mobilize than a big truck.”
The biggest drawback with the trailer-mounted systems is water flow. If root infiltration is an issue, then an under 30-gpm system is not going to have the power to cut through the root system. In addition, due to the lower water flow, the smaller trailer units don’t have the power to effectively clean pipes larger than 24 in. in diameter.
Matching Water Flow and Nozzles
“Before you purchase a unit, it’s important to fully understand the type of work that needs to be completed,” says Moore. “Then be sure to select a sewer-jetter unit that will produce the water flow necessary to effectively accomplish the task at hand. While water pressure is a consideration, the water flow rate really is the determining factor. We offer two water flow rates — 12 gallons per minute at 3,000 psi and 25 gallons per minute at 2,500 psi.”
Why the difference? Well, it really boils down to what you are trying to remove from the sewer pipe and the type of nozzle you plan to use. It’s more of a gallons-per-minute function. With each nozzle you want to make sure you have got enough water flow to effectively complete the job.
“It’s all in proportion,” says Moore. “Many times you can use the same nozzle on a 12-in. and a 24-in. pipe as long as what you’re trying to accomplish is the same. If you are cleaning the sides of the pipe, then you need a nozzle with a lot of outside pressure going to the walls to get that pipe clean. Removing a clog requires a forward-cutting nozzle. In the case of root infiltration, then you might use a specialized cutter that goes onto the nozzle and a water flow rate of at least 45 gallons per minute.”
Moore encourages customers to work with the sewer-jetter manufacturer about the task at hand so they can help you match the appropriate water flow rate to the correct nozzle. It’s also important to match the appropriate diameter hose to the nozzle. Too small of a diameter hose will limit water flow to the nozzle and reduce its effectiveness.
It’s also important to make sure the unit has a good quality vacuum blower with suction strong enough to remove the debris flushed from the pipe. The size of the holding tank is also a consideration. If you’re pumping 12 gpm and have only a 100-gal holding tank, then within nine minutes the tank will be full.
Routine Maintenance and Safety Considerations
Maintaining the integrity of the nozzles is important. Make sure they are working properly with regular inspections and cleaning of the heads as needed. If the nozzles begin to wear, they likely will not hold the required pressure to effectively clean the pipe and should be replaced. Also, inspect the lead section of the hose. This portion is more rigid than the rest of the hose and can wear easily. If wear does begin to appear, it should be replaced.
From a safety standpoint, make sure the nozzle is completely inserted into the sewer pipe before you turn the system on. If this is not done, the hose will begin whipping and could cause injuries. Most importantly, before entering the manhole to position the sewer-jetter hose, test the air quality and visually inspect the area for any safety concerns and then make sure no one enters the manhole during the sewer-jetting process.
Depending on your needs, a trailer-mounted sewer-jetter system may be the ideal solution to your small-diameter sewer cleaning projects. Plus, since the heart of a trailer-mounted sewer-jetter system is a hydro excavation vacuum, you get some added versatility to help clean catch basins and pothole for utilities.
“It’s a lower-cost method of getting in and getting your pipes cleaned,” says Moore. “Plus it offers better maneuverability and gives you an option to do more than just sewer jetting down the road.”
Greg Ehm is a technical writer with Two Rivers Marketing, based in Des Moines, Iowa.