Gibbons HVAC engineers recently completed the inspection of the main portal axial fans in a major UK road tunnel. The site visit was intended to specifically assess the overall condition of the extract fans using portable condition based monitoring equipment.
Ventilation in road tunnels is essential to avoid the accumulation of vehicle exhaust gases, ensuring air quality for people inside and facilitating a safe evacuation during emergencies by controlling smoke caused by fires. Ventilation systems within road tunnels have dual roles: firstly, mitigating vehicle-generated pollution, and secondly, functioning as a crucial component of the emergency life safety system to handle smoke produced during a fire.
Information from the readings
The readings taken were with our own calibrated measuring equipment, using long leads to reach out of the large fan case. There are two types of vibration data collected from each monitoring sensor. mm/sec2 readings are used to locate problems such as motor defects, fan impeller balance defects, fan rotor blade problems, alignment problems, mechanical looseness, resonance, drive belt problems, airflow and turbulence problems.
Readings taken in “G’s” are used to locate early signs of bearing defects and bearing wear, gearbox, gear mesh and gear tooth problems, lubrication problems and look at very specific frequencies that relate to these issues.
The road tunnels are two twin-lane, uni-directional road tunnels. Both have complex ventilation systems consisting of a semi-transverse system together with additional jet fans to control longitudinal flow. In both tunnels, the semi-transverse ventilation system has two shafts with axial extraction fans located at a relatively short distance from each of the tunnel portals. The semi-transverse system supplies fresh air into the tunnel through grills along the side of the roadway between the extract shafts. The fresh air is pumped into the invert under the roadway using two axial fans at opposite ends of the tunnel.
Results after testing
The results obtained from our experts show that despite their age, there are only some minor issues within the key components of the fan. This is the assembly of the motor and gearbox and to a lesser extent the fan impellers. During the tests, the Gibbons engineers were able to take readings directly from the gearbox in these unusual fan assemblies, and from the fan motor using a portable, calibrated condition based monitor.
The purpose of the site visit wasn’t necessarily to undertake mechanical assessments, but it is an important factor in the planning for future maintenance. After assessment from Gibbons Engineers, it was reported that the fans are in good working order. We highlighted some corrosion on the fan impellers around the upper edges of these older fans. This would need to be addressed after a detailed inspection by our mechanical engineers.
After the inspection and assessment of the fans, a full report was completed by Gibbons Engineers, with detailed results and findings, and recommendations for future maintenance of the tunnel fans.