‘Traditionally in this country, people want big equipment. They want to crush a gnat with a sledgehammer, and you don't need to do that,” said Nick Woodhead, president of U.S. Jetting, a sewer cleaner manufacturer based in Alpharetta, Ga.
Applying that thought to sewer-cleaning equipment, Woodhead is saying that you need to select the proper pressure and volume of your water jet for the size of pipe and material that you're trying to clean. An average sewer pipe, for example, is 4 to 12 inches in diameter and has tree roots and grease in it.
“For that I'm going to recommend fairly high pressure and a medium-volume unit,” said Woodhead. “I'm going to recommend a unit that puts out water at 4000 psi and 18 gallons per minute.”
On the other hand, for cleaning sand from a storm sewer, you want a high-flow unit, said Don Buckner, president of Vac-Tron Equipment in Okahumpka, Fla. “You want 50 to 60 gallons per minute, and about 1500 to 2000 psi. You want high flow because the water erodes the sand back to the catch basin, just like a river erodes the sand on its banks,” he said.
Regular cleaning of catch basins is required under Phase II Stormwater Regulations of the National Pollutant Discharge Elimination System (NPDES), Buckner said. NPDES requirements have resulted in an increase in large truck vacuum cleaner sales.
Water jetters are available on trucks or trailers, and so are vacuum cleaners. Or, you can buy a combination unit with both a jetter and vacuum cleaner. “Historically a lot of cities like the combination of jetting and vacuum units,” said Woodhead. “But in my opinion, you're really better off to have two separate machines because most people only run one operation at a time—jetting or vacuum cleaning.”
When sizing a liquid-only vacuum cleaning unit, you need 10 gallons of debris storage for each cubic foot per minute (cfm) of air moving on your vacuum, Buckner advised. So if you have a 2000-gallon tank, you need to be moving 200 cfm of air with your vacuum.
If you're cleaning liquid waste only—sludge for example—it requires a relatively small cfm number but high pressure as measured in inches of mercury, say 25 to 26 inches. The pressure is analogous to the horsepower of the unit, Buckner said. For cleaning sludge from a sewage treatment plant, it's best to use a high-mercury rotary vane pump that seals itself with oil.
“A rotary pump not only pulls air out of the tank, it can reverse the air flow and push air into the tank to discharge it,” said Buckner. Typically sand will not flow out of a tank, so you have to physically dump it out. To do that you need a large rear door on the tank. Vac-Tron builds both trailer- and truck-mounted vacuum units.
If you're going to jet-clean sewers in remote areas, you'll need to carry as much water as possible to minimize travel time to get water, said John Butler, sales coordinator for Hi-Vac Corp., Marietta, Ohio. Plus, when you go to discharge the tank, you want to carry as much debris as possible—and as little water as possible. That means you want to drain off the excess water before going to dump the tank. Butler said Hi-Vac's Aquatech units are built so that debris enters the top of the tank and settles toward the front, so extra water is pushed to the back, where it can discharge easily through a 6-inch-diameter drain.