Manholes in pipeline systems: In which type of pipe material are manholes (access chambers) least commonly provided, considering typical use as pressure mains versus gravity sewers?

Introduction / Context:
Manholes are vertical access structures primarily associated with gravity sewers to facilitate inspection, cleaning, and maintenance. Pressure water mains, in contrast, commonly use appurtenances such as air valves, scour valves, hydrants, and inline isolation valves rather than manholes at intervals.

Given Data / Assumptions:

• Cast iron and steel pipelines are typically used as pressure mains for water supply.
• R.C.C. (reinforced cement concrete) pipes are widely used for gravity sewers where manholes are necessary at junctions, changes in direction, and specified spacings.
• Hume steel pipes are also used for pressure conveyance.

Concept / Approach:
Manholes are not installed “on” pressure pipelines at intervals because there is no open channel flow to enter; access is instead via valve chambers. Gravity sewers (often R.C.C., stoneware, or PVC) require manholes for maintenance. Therefore, among the listed materials, manholes are least common with cast iron pressure mains (similarly steel and Hume steel), but the canonical exam answer singles out cast iron pipes.

Step-by-Step Solution:
Identify which materials serve pressure mains: cast iron, steel, Hume steel.Recognize manholes belong to gravity sewers (often R.C.C.).Choose the pressure-main material typically cited in exams: cast iron pipes.

Verification / Alternative check:
Water distribution drawings show valve/air valve chambers on pressure lines, not manholes. Sewer layout plans show frequent manholes on R.C.C./stoneware sewers.

Why Other Options Are Wrong:

• Steel and Hume steel: also pressure mains with no routine manholes, but the conventional single-answer choice is cast iron.
• R.C.C. pipes: widely used for gravity sewers; manholes are common.
• Ductile iron pipes: also pressure mains; not typically provided with manholes.

Common Pitfalls:

• Confusing valve chambers (on pressure lines) with manholes (for gravity sewers).
• Assuming material alone dictates appurtenances; the flow regime (pressure vs gravity) is decisive.

Final Answer:
cast iron pipes