Vibration monitoring system helps
keep Mersey Tunnel running.

Mersey Tunnels are using a multichannel vibration monitoring system for measuring the vibration levels of the fan ventilation system in the tunnels acting as a preventative maintenance aid by providing them with data to plan when service and repair work can be carried out.

Entrance to the Mersey Tunnel

The Kingsway Tunnel has two 2.2 kilometres long tubes which connect Liverpool to Wallasey, providing an important traffic route for both commuter and heavy goods vehicles. The latest tunnel is now 30 years old and with its four traffic lanes links Liverpool with the Wirral giving fast access to the M53 motorway and the Freight Ferry Terminal to Ireland.

In the tunnel are eight sets of ventilation systems with both extract and blow, four of the sets being on standby. Each system uses extremely large fans with blade diameters of up to 3.5 metres. The level of carbon monoxide and smoke density are both monitored manually and at excessive levels the operator can change the fan speed or, in the event of fan failure, bring a standby fan on line.

The multichannel Monitoring
System operating on a fan

Each fan is driven through a Radicon gearbox, the bearings of which are monitored for vibration levels. When these levels become excessive, maintenance engineers can switch over to the four standby fans and move in to carry out service or repair work.

One of the eight set fans
for both extract and blow.

Because the fan systems are in robust casings, the components cannot be seen or accessed easily, which eliminates manual monitoring with a portable vibration meter. Mersey Tunnels overcame this by fitting a permanent vibration sensor at each point on the eight fan systems, giving continuous simultaneous vibration readings for the
whole tunnel.

All of the sensor signals are cabled into the multichannel vibration monitoring system housed in an industrial enclosure, which provides sensor excitation, signal conditioning, level indication and pre-set alarm level triggering via relay units.

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March 2005

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