The Sewer Maintenance Division has a maintenance and cleaning program to keep the sanitary sewer system operating efficiently and to minimize the number of calls for service. Sewer cleaning using hydraulic or mechanical methods performed on a routine basis helps to remove accumulated debris in the pipe such as sand, silt, grease, roots and rocks. If debris is allowed to accumulate, it reduces the pipe capacity and a blockage can eventually occur resulting in overflows from the system onto streets, yards, basements, and into surface waters.
The Sewer Maintenance Division has five full time cleaning crews with each crew assigned to one of five designated cleaning areas in the town. A cleaning crew typically consists of a crew chief and two maintenance men. We use high-pressure sewer jet trucks, trailer mounted bucket machines and sewer vacuum trucks to clean the sanitary sewer system.
Our high-pressure sewer jet trucks carry between 1,500 and 2,000 gallons of water. The vehicle’s high-pressure pump can pump out up to 65 gallons of minute at around 2,000 psi for cleaning out the sewer pipes. A typical truck can carry 700 feet of 1-inch diameter high-pressure hose, which is inserted into the sewer during cleaning operations. The sewer jet can power a variety of sewer cleaning apparatus.
The following is a list of sewer cleaning methods presently in use by our division:
1. High Pressure Flushing
This method uses high-pressure water to flush out stone, sediment or other unwanted material from the sewer. Our sewer cleaning trucks can generate 2,000 psi of water pressure with a flow rate of 65 gallons or more per minute. As comparison, a typical household gas engine pressure washer can produce around 2,000 psi of pressure, but only with a flow rate of around 2.5 gallons per minute. It is the combination of high pressure and high flow rates that cleans the pipe. A flushing nozzle is installed on the end of the jet truck’s hose and the hose is lowered into the downstream manhole of the sewer section being cleaned.
There are a number of rear facing jets in the circumference of the nozzle that allow the high pressure water to propel the flushing nozzle and sewer hose up the sewer to the next manhole, which is usually no more than 300 feet away. As the nozzle moves up and down the pipe, it dislodges sediment, stone and other debris and flushes it downstream to the manhole, where it is removed from the sewer.
There are a variety of cleaning nozzles, each tailored for removing certain materials from the sewer system. Some examples are penetrating nozzles, which have one frontward facing nozzle to penetrate a blockage and break it up and spinning nozzles, which spin and scour the pipe walls during cleaning. A culvert nozzle is used to clean pipes in excess of 15 inches in diameter, because all of the jets are located on the bottom of nozzle.
High-Pressure flushing is typically used to clean sewers with polyvinyl chloride (PVC) pipe, reinforced concrete pipe (RCP), vitrified tile pipe (VTP) and asbestos cement pipe (ACP). Although high-pressure flushing is good at cleaning sediment and stones out of the sewer system pipes, it cannot cut roots, which are typically found in the older areas of the Town, which were constructed with vitrified tile pipe (VTP) “clay pipe”. Tree roots can penetrate the joints and cracks of this type of sewer pipe and must be cut out using root cutters or bucket machines.
2. Root Cutters
This method uses the high-pressure water from the sewer jet truck to operate a hydraulic root cutter. The high-pressure water turns a hydraulic motor, which has a root cutting blade attached to the motor shaft. As with the cleaning nozzles, there are rear-facing jets on the root cutter assembly, which propels the cutter up and down the sewer pipe. All cut up roots and debris is flushed down to the manhole where it is removed from the sewer system. There are a variety of root cutters to clean sewers ranging from 6 to 21 inches in diameter. Although bucket machines can be used to clean smaller pipes, we prefer to use root cutters because they are fast, efficient and cause less "trauma" to the pipe than the bucket machines. We use bucket machines to clean sewers in excess of 18 inches in diameter.
3. Bucket Machines
This method uses trailer mounted bucket machines to clean roots and debris from the sewer system. Bucket machines to clean sewers in excess of 18 inches in diameter. Bucket machine units have a steel framework on which a gas engine and drum winch is mounted. The drum is connected to the engine through a controllable drive train and holds 1,000 feet of ½ inch steel cable. Two units are needed for this operation, each being positioned over successive manholes to pull the buckets back and forth in the sewer line. The steel cable is initially strung through the sewer with a high-pressure cleaning nozzle and sewer jet truck. The machine that pulls the bucket out of the manhole has a boom, which is used to swing and dump the material. Cable guide jacks are positioned down in both manholes to prevent the cable from rubbing or cutting into the pipe. The buckets for the bucket machines range from 8 to 30 inches.
4. Sewer Vacuum Trucks
Sewer vacuum trucks are used to vacuum out sediment, sand, stone, bricks rocks or other debris cleaned out from the sewer system. The vacuum truck can be used in conjunction with the sewer jet during cleaning operations when the sewer is too deep to clam out the material by hand or when an abundance of material is brought back to the manhole.