Hydraulic control systems for and methods of controlling the operation of tunnelling apparatus

In or for tunnelling apparatus which employs a drive shield, a concrete-reception space defined rearwardly of the drive shield to receive concrete, during use, to produce a lining for the tunnel, the space being delimited at the front end by an annular member and double-acting hydraulic rams with first and second working chambers usable to position the annular member;

• an improved control system for controlling the operation of the rams, said system comprising pumping means for providing hydraulic pressure fluid for charging the working chambers of rams, said pumping means at least including a plurality of individual pump units and a main pump and means for selectively connecting the respective working chambers of the rams to the pump units and to the main pump, wherein the first working chamber of each ram receives pressure fluid from the main pump when the connecting means is set to make the annular member move up towards the drive shield and the second working chamber of said ram, which tends to decrease in volume when the connecting means is thus set, is connected to a respective one of the pump units which then functions as a brake motor.