Pumps used during tunnel construction: Long service life is crucial


Courtesy of Courtesy of ALLWEILER GmbH

'Years of reliability is our first priority,' according to engineer Albert Feisst, the director of liquid engineering who is responsible for all pumps used in Herrenknecht AG tunnel boring machines. Headquartered in southwest Germany, Herrenknecht is a global market leader in its industry. For more than 30 years, pumps from Allweiler AG have played a key role in these machines. Some tunnel boring machines are the size of a house and contain nearly every type of pump manufactured by Allweiler AG.

Robust screw pumps
Screw pumps of the 'SNS' and 'SNF' series carry feed oil for the entire hydraulic system at a pressure of 25 to 50 bar. They lubricate the gearboxes with low-viscosity oil (up to approximately 460 mm2 /sec) at pressures up to 60 bar. Pumps of the 'Trilub“ series are used in the hydraulic system's cooling circuit and as filter pumps alongside units of the “SNS” and “SNF” series. These pumps operate at pressures of approximately 16 bar. All of these pumps have proven their durability and longevity in dozens of cases. 'These pumps often stay in service for two to three years without maintenance. During this time we will use them in four or five of our machines,' according to Mr. Feisst. Individualized, highly precise configuration of the pumps by the manufacturer is a key aspect of achieving such tremendous durability.

In addition, these pumps are very insensitive to disturbances. It is not uncommon for chips to enter the gear oil the first time a machine is started and during the gearbox's run-in phase. It is essential that this not lead to disturbances in the pump. Screw pumps have also proven to be extremely reliable when temporarily operated under cavitation and aeration conditions.

“Trilub” pumps are characterized by a very long service life in the mid-pressure range. 'These pumps are designed in a way that give them a very good price/performance ratio,' according to Mr. Feisst. Pumps designed for higher pressure have a pressure relief valve for additional safety. This helps avoid excessive pressure conditions and damage to the overall system. 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. Finally, 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.

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