A Non-Invasive Way to Find Blockages in Sewers and Drains: The Reflected Wave Technique.
Key takeaway.
Blockages and sediment build-up in drainage pipework are hard to locate without excavation or camera surveys. This research develops the reflected wave technique, a non-invasive method that sends a low-frequency air-pressure wave down a drain and reads its reflection to locate partial blockages from a single access point.
The study.
Blockages, sediment, and partial obstructions inside buried sewers and drains are difficult and costly to locate. Conventional diagnosis relies on excavation or camera surveys, both of which are slow, disruptive, and limited in reach. Kelly and colleagues set out to develop a faster, non-invasive alternative that works from a single access point.
The reflected wave technique introduces a low-frequency air-pressure wave (approximately 10 Hz) into the pipe and measures the wave reflected back from any change in the pipe's cross-section. Because a blockage reduces the pipe's effective diameter, it reflects a characteristic signal whose timing indicates the distance to the obstruction. In a test rig representing roughly 70 m of drainage pipework, the technique detected and located both 30% and 75% partial blockages without excavation or fixture removal.
The reflected wave approach has separately been applied by the same research group to detecting depleted appliance trap seals in earlier work, but the 2024 study reported here is specifically about locating blockages and sediment accumulation in sewers and drains. It represents a meaningful advance in building diagnostics, giving facility managers a rapid, non-invasive way to identify where a drainage line is obstructed.
Key findings.
- Non-invasive single-access-point detection The reflected wave technique locates blockages from a single access point, enabling rapid screening of a drainage line without disruptive excavation or camera surveys.
- Partial blockages detected and located In a test rig representing roughly 70 m of pipework, the technique detected and located both 30% and 75% partial blockages, and the timing of the reflected wave indicated the distance to the obstruction.
- Low-frequency air-pressure wave A low-frequency wave of approximately 10 Hz is introduced into the pipe; a reduction in the pipe's effective cross-section reflects a characteristic signal back to the sensor.
- Applicable across pipe configurations The reflected wave technique works across various pipe geometries and materials, supporting drainage system assessment in a range of building configurations.
- Related to earlier trap-seal work The same reflected wave principle has separately been applied by the research group to detecting depleted appliance trap seals in earlier studies; this 2024 paper focuses on blockage and sediment detection.
What this means for your facility.
Kelly and colleagues address the detection side of drainage maintenance: finding where a line is obstructed after a problem has developed. Diagnostic tools like the reflected wave technique are valuable for locating blockages and sediment, but they operate reactively. They find issues once they occur, and the remediation still has to follow.
Green Drain sits on the prevention side of the same maintenance picture. A conventional trap relies on standing water to hold its seal, and that water can evaporate when a drain is used infrequently, leaving an open pathway between the drainage system and the room. Green Drain's waterless one-way valve removes the standing water a conventional trap relies on, so there is no water to evaporate. The valve stays closed between uses and opens only to let flow pass, functioning as a supportive engineering control that restricts the upward movement of air and aerosols from the drainage system into the occupied space.
Green Drain is a passive engineering control, not a diagnostic tool, and it does not remediate or remove an existing blockage or biofilm. It complements, rather than replaces, routine drainage maintenance and inspection. The ASSE 1072-2020 standard describes the sustained seal integrity expected of a trap seal device across its service life.
For healthcare, food service, and other facilities that run inspection or diagnostic programs on their drainage systems, Green Drain fits alongside that work as a passive seal on the fixtures most at risk of evaporative dry-out, restricting the upward movement of air and aerosols without a detection-and-remediation cycle for the seal itself.
Full citation.
Related research.
Protect your facility's drains.
Green Drain's waterless trap seal is a supportive engineering control that restricts the upward movement of air and aerosols, backed by independent bench testing. See how it works for your industry.