Compound Engines — Effective Crank Relationship in Tandem Type In a tandem-type compound steam engine, the high-pressure (HP) and low-pressure (LP) cylinders are aligned on the same piston rod and act on the same crank. The effective crank positions of HP and LP are regarded as:

Introduction:
Compound engines can be arranged as cross-compound (separate cranks) or tandem (same crank). The geometric relation between crank positions determines torque phasing and influences vibration and flywheel sizing. This item asks about the special case of tandem compounding.

Given Data / Assumptions:

• Tandem compound configuration with a common piston rod.
• Both cylinders drive the same crank pin.
• Standard double-acting steam cycle.

Concept / Approach:
If both cylinders act on the same crank, their effective crank angles are coincident. Hence the phase difference is 0°. This contrasts with cross-compound engines where the cranks are often set 90° apart to even out turning moment.

Step-by-Step Solution:
Note mechanical link: one crank pin shared.Deduce geometry: both piston motions reference the same angular position.Therefore, effective crank positions are 0° apart.

Verification / Alternative check:
Mechanism schematics for tandem compounds show the HP cylinder bolted to the LP cylinder in line, sharing rod and crosshead, which necessarily implies the same crank phasing.

Why Other Options Are Wrong:

• 90° or 180°: applicable to multi-crank layouts, not tandem.
• None: unnecessary since the correct relation is definitive.

Common Pitfalls:
Confusing tandem compounding with cross-compounding where phase angles are chosen to smooth torque.

Final Answer:
0° to each other