Exam Question

### (a) A Single-Throw Crank for a Multi-Stage Compressor (4 Marks)
A single-throw crank design for a multi-stage compressor, typically in a tandem arrangement, is desirable for several key operational and design reasons:
* **Compact Design & Space Saving:** In this configuration, the low-pressure (LP) and high-pressure (HP) pistons are mounted on a common piston rod, connected to a single crankpin via one connecting rod. This vertical stacking results in a significantly smaller footprint compared to a design with separate cranks for each stage. This is a critical advantage in confined machinery spaces onboard ships.
* **Improved Mechanical Efficiency & Balance:** The forces acting on the running gear are partially balanced. The upward compressive force from the larger LP piston is counteracted to some extent by the downward force from the smaller HP piston acting on the same assembly. This leads to a smoother torque diagram, reduced bearing loads, and better overall mechanical balance, contributing to a lower power-to-weight ratio.