Schwalm System: Innovative Compression Plug for Blind Connections

Unused junctions branching off sewers, so-called blind connections, are problematic. They are often not watertight and as a result water in the surrounding earth is able to enter the sewer system. Sewage treatment plants, however, prefer undiluted effluent. On top of this comes the fact that blind connections offer an ideal abode for rats – they build their nests behind the branch junctions. For reasons of hygiene a questionable state of affairs. Schwalm Kanalsanierung (Bad Hersfeld) has developed a blanking plug that helps to solve the problem, with a clever robotics system enabling precise fitting and removal from inside the sewer.

The Situation: When the Watertightness Test Results in a Call for Action

The Water Management Act requires initial testing of all sewerage system lines until December 31, 2015 throughout Germany. For the experienced practitioner this is not a reason for exaggerated delight. This is because leaky lines are quite usual. In this, the focus is on unused or insufficiently – or not at all – sealed field and blind connections, amongst other things. These are called erroneous connections. Along with the oozing losses undesired from an ecologic point of view, they particularly result in the penetration of ambient water into the canalization, like all leaky spots, diluting the load up to 600 times. An effect not appreciated by sewage disposal facilities. Because a certain load of dirt is even desired for the efficiency of the sewage disposal stages.

Highways and Side Doors for Rats

Rats use main lines as quick connection routes between A and B. On the contrary, they erect their domiciles in protected spots. Blind connections – particularly open ones – are suited nearly ideally as nesting places. The invitation is perfect: rats build their caves behind the open nozzles. This is also a reason for making sure that the lines are sealed solidly and tightly.

Solution Concept: The Compression Plug for Blind Connections

Schwalm Kanalsanierung developed a procedure that can be used to tightly seal blind and field connections – even subsequently. In this, robots are used to mount a compression plug corresponding to the pipeline diameter from the inside, whereby these robots may also remove the compression plug, if required. Of course, the compression plug can also be attached and removed manually from the outside using a wrench. The compression plug procedure is suitable for main lines with a diameter of DN 200 to 600 and lateral lines with a diameter of DN 150 to 250. The compression plug withstands a required air pressure of 0.2bar. During laboratory testing, the plug achieved a maximum pressure resistance value of 1,5bar.


The mentioned robots and compression plugs are part of a range of products of the manufacturer Schwalm adapted to sewer rehabilitation. It consists of rehabilitation robots, lateral connection packers, special vehicles with control consoles for robotics, video diagnostics and workshop for remotely controlled milling, chiseling, jetting, placing liners and hats. As developer and manufacturer, Schwalm relies on its experience as service provider and uses the on-site work directly as "development laboratory" on its own account. Sewer rehabilitation companies from all over Europe use Schwalm's technology.

Published in the RO-KA-TECH Journal 03/2006

Schwalm Robotic GmbH Industriestraße 16 36251 Bad Hersfeld-Asbach Germany Telefon: +49 6621 79578-0 Telefax: +49 6621 79578-11