Pumps help excavate world’s longest tunnel

Copyright © BBT SE

The Brenner Base Tunnel through the Alps, destined to become the longest underground railway connection in the world at a planned length of 64 kilometers, is being excavated using tunnel boring machines, or TBMs made by Herrenknecht. The TBMs contain nearly every type of pump manufactured by Allweiler, a Circor brand;

  • Filter oil and cooling system pumps
  • Grout pumps for ring-gap mortar injection
  • Proportioning pumps with quench`
  • Water pumps

Herrenknecht’s director of fluid engineering for traffic tunneling, Albert Feisst, needed to source pump systems that could comfortably deliver a service life to the TBM of 15 years. Every pump and drive used in TBMs must be dimensioned so that pump performance will never be exhausted during normal operations.

Filter oil and cooling system pumps

To achieve a maintenance-free service life of 2-3 years for these applications, Circor recommended three-screw pumps. These carry feed oil for the entire hydraulic system at a pressure of 25-50 bar and lubricate the gearboxes with low viscosity oil (up to 460 mm2/sec) at pressures up to 60 bar. Alongside these, other three-screw pumps are used in the hydraulic system’s cooling circuit and as filter pumps, at pressures of 16 bar. These pumps are proven to be insensitive to the disturbances that can occur at machine startup and during the gearbox’s run-in phase; they are also very reliable when temporarily operated under cavitation and aeration conditions.

Some of the three-screw pumps used, in the Trilub series, offer a very long service life in the mid-pressure range. Pumps designed for higher pressure have a pressure relief valve for additional safety.

For more than 30 years, Allweiler pumps have played a mission-critical role in Herrenknecht’s TBMs. “Allweiler is the best supplier we have when it comes to service and customized solutions,” Feisst said. “Their pumps often stay in service for two to three years without maintenance.”
Because Herrenknecht’s TBMs are in operation around the world, having easy access to local support is another imperative. With nearly 100 subsidiaries and partners around the globe, Allweiler readily meets this requirement.

Additional pressure-maintaining and control valves keep system pressure steady as consumption fluctuates. Piston-based pilot control of the valves results in very small hysteresis values and therefore fine control over the pumps. An optional control-oil filter prevents foreign objects from clogging the control nozzles and contaminating the valves. Solenoid valves and controllers allow the operator to preselect several different system pressures and start the pumps in an unpressurized condition. This makes it possible to have virtually pressure-free circulation and operation, such as when starting the pump or when the system stops for a short period of time.

Grout pumps for ring-gap mortar injection

TBMs use steel-reinforced concrete profiles known as tubbing to stabilize the tunnel walls in newly dug sections. The space between the ground and the tubbing must be filled with a special two-component mortar and compacted. Progressing cavity pumps move this bentonite-cement suspension to fill the empty spaces with pressures of up to 20 bar and capacity of up to 120 liters per minute. To ensure that the suspension quickly cures and hardens, a separate progressing cavity pump adds the accelerator component to the discharge side of the pump. To ensure no contact with the ambient atmosphere, mechanical seals are secured with a pressureless quench with a hydraulic seal.

Proportioning pumps with quench for accelerator

Progressing cavity pumps also move the foaming agent tenside dissolved in water and polymers to keep dust down and lubricate the cutting tools. This approach produces the best results, especially with non-cohesive, water-permeable ground. These pumps operate in a pressure range up to 16 bar and a capacity of 0.2-2.5 liters per minute.  A very steep performance curve is required so that the pump will proportion liquids precisely even when capacity and speed are low.

Water pumps

Finally, centrifugal pumps move water at high pressure. All pumps utilize frequency converters to operate across a wide control range. These devices precisely adjust capacity to the oversized drives. The optimized controllers enable pumps to deliver good efficiency with low energy costs even when working below their performance limits.

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