Compound engine layouts: In a Tandem-type compound steam engine, how are the high-pressure (H.P.) and low-pressure (L.P.) cylinders mechanically arranged?

Introduction / Context:
Compounding expands steam successively in two or more cylinders to improve efficiency and smooth torque delivery. The layout of these cylinders defines important mechanical and thermodynamic features of the engine.

Given Data / Assumptions:

• Two-cylinder compound engine (H.P. and L.P.).
• Question asks about the mechanical arrangement in the “Tandem” type.
• Standard nomenclature: tandem vs cross-compound vs receiver types.

Concept / Approach:
In a Tandem compound engine, the H.P. and L.P. cylinders are in line and share a common piston rod. The pistons move together, transmitting force through a single rod and usually a single crosshead. Steam exhausted from the H.P. immediately enters the L.P. cylinder, often without a large external receiver volume.

Step-by-Step Solution:
Identify the keyword “Tandem” → in-line cylinders on one axis.Mechanical linkage → a single, continuous piston rod serves both cylinders.Contrast → cross-compound engines use separate rods and cranks set typically at 90°.Conclude → correct choice: “have common piston rod”.

Verification / Alternative check:
Historical engine diagrams show the H.P. mounted ahead of the L.P. on the same rod and crosshead, confirming the definition.

Why Other Options Are Wrong:
Set at 90° / separate rods / V-arrangement / independent axles: these describe cross-compound or multi-cylinder I.C. layouts, not tandem compounding.

Common Pitfalls:
Confusing “tandem” (mechanical alignment) with “receiver” (thermodynamic feature of inter-stage volume).

Final Answer:
have common piston rod