Traditionally, work in sewers is conducted both above and below ground, with crews opening manholes and descending into the sewers, thus causing road closures and traffic jams. But thanks to modern robotic technologies— powered by small but mighty air motors—clearing out sewer networks and rehabilitating them can be done safely and without impacting the world above.
Sewer maintenance tools now include special cameras and milling robots, such as the ones from BRM GmbH, Biebergemünd, Germany, says Günter Meister, managing director. The camera provides a first visual inspection of the sewer pipes. “The camera head—our own design—can be swiveled 270° horizontally and 400° radially,” Meister said. “This ensures that the specialists are able to inspect the pipe walls in minute detail, and determine any damage.”
Once the initial inspection has taken place, the small but powerful milling robot starts its work. The rotating milling head, with its diamond-studded surface, devours ingrown tree roots, broken-off pipe splinters and hardened, encrusted muck, thus removing any blockages in the pipes. The milling robot consists of a two-axle trolley to move the robot forward and back inside the pipe. Two hydraulic cylinders are fitted to the trolley. They tip the milling arm up and down or forward and back. The control electronics are also fitted to the trolley.

BRM’s milling robot F170, which uses customized air motors to deliver high power in adverse conditions. Photo courtesy of BRM.
A flange-mounted circle gear turns the milling arm, and the air motor is carried on the milling arm itself. This motor supplies the power for the milling work and causes the milling head to rotate. At the command console the operator manipulates joysticks and switches to control the milling robot. The special camera fitted to the milling arm monitors the work underground and transmits the images to a monitor. It means that the specialists are constantly able to monitor the progress of the cleaning work.
BRM GmbH supplies two different sizes of milling robot—the F130 for DN150 to DN300 pipe widths, and the F170 for DN200 to DN600 pipes. And now, the larger milling robot is available with even more power, thanks to a new air motor from DEPRAG Schulz GmbH, Lewisville, Texas, which gives the F170 twice the power.

BRM’s milling robot F170 entering a sewage tunnel. Photo courtesy of BRM.
According to application technician Sven Menzel at sewer maintenance company GM-San UG, the output is much higher than the previous design. “On a project with 35 branch pipes, we previously required 1050 working minutes to carry out the job. With this new air motor we had completed the work after just 525 minutes. That is an enormous saving in time and operating costs.”
DEPRAG, which specializes in customizing its line of air motors for different applications, supplied an air vane motor from its Individual Line onto the milling arm of the robot.
After testing several air motor designs, BRM’s Meister said that no other air motor achieved such high removal rates.
The air motor, which has been specifically developed for use in the milling robot, has a square housing. The power pack is 145 mm long and 70 mm wide, so is ideal for small, tight spaces. It occupies just a third of the size and has a fifth of the mass of a comparable electric motor.
Air vane motors operate on a very simple principle: The compressed air—generated by a compressor—causes the air motor to rotate. In air vane motors, the rotor—which rotates inside an eccentric cylinder—is set into motion. Vanes are inserted into the slots of the rotor and the centrifugal force that arises presses them outwards. This creates work chambers for the expanding compressed air. With this expansion the compressed air that feeds through converts the pressure energy into kinetic energy—causing rotational motion. Air motors can operate optimally within a wide range of changing loads, because the power output remains almost constant over a wide speed range. Motor power is adjusted by changing the operating pressure, while speed is controlled by smoothly throttling the air quantity.

Milling robot F170 getting ready to clear out a sewage tunnel. Photo courtesy of BRM
The air motor can cope with a variety of workloads. Meister added, “If the milling head encounters what appears to be an indestructible obstacle and comes to a standstill, it suffers no damage. In the event of overload the air motor simply stops, and once the load abates it starts up again immediately. And this can happen over and over again even for extended operating cycles. In short, it is the ideal drive for our milling robots. This air motor cannot overload and suffer damage.”
To counter the adverse conditions of wet, aggressive contamination inside the sewer pipe this pneumatic drive is coated with an anti-corrosion protective coating. Additionally, before the milling robot descends into the sewer system, the air motor is charged with compressed air, meaning that moisture and contaminating particles cannot penetrate into the internal overpressure of the unit, because the air motor more or less “seals” itself, making it resistant to all types of contamination inside sewer pipes.
After the milling robot has cleared the pipes of muck and ingrown tree roots, and sewer inlets and outlets are sealed up, defective sections of pipe are refurbished rather than replaced. They are lined from inside with prepared special film tubes called inliners, thus sealing them from any potential leaks. Then, the milling robot is deployed a second time. A ball-head is used to ensure that the inlets and outlets are now properly reopened.
Applications technician Sven Menzel of GM-San UG concluded, “With the F170 and the new DEPRAG air motor the work involved in opening the branch-outs is much faster.”
DEPRAG Schulz GmbH & Co
www.deprag.com
BRM GmbH
www.BRMGmbH.de
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