What is the difference between a single acting and double acting hydraulic cylinder in a TBM system, and why is this relevant?

The key difference lies in how the cylinder extends and retracts. A single-acting hydraulic cylinder uses hydraulic pressure to extend the piston in one direction only. Retraction is typically achieved by a spring or by gravity. A double-acting hydraulic cylinder uses hydraulic pressure to both extend and retract the piston. This is achieved by having two separate ports for applying hydraulic pressure, one for extension and one for retraction. This is relevant in a TBM system because different applications require different types of cylinders. For example, a single-acting cylinder might be used for a simple clamping function where a spring return is sufficient. A double-acting cylinder is needed for applications requiring precise and controlled movement in both directions, such as the main thrust cylinders that push the cutterhead forward. The choice between single-acting and double-acting cylinders affects the TBM's control, efficiency, and complexity. Double-acting cylinders provide more precise control but require more complex hydraulic systems. The term 'hydraulic cylinder' refers to a device that converts hydraulic pressure into linear motion. 'Piston' is the moving component inside the cylinder. 'Hydraulic pressure' is the force exerted by a fluid under pressure.