Valves in water-supply – seating form for a valve fitted in a recess against a pipe opening The valve that seats closely in a machined recess at an opening in a pipe typically uses which disc/closure form?

Introduction / Context:
Distribution systems use several valve types. The geometry of the closure element determines seating, loss characteristics, and suitability for isolation or throttling. A valve that closes into a recess in line with the pipe opening is generally a gate (sluice) valve.

Given Data / Assumptions:

• Valve is intended primarily for isolation (fully open or fully closed).
• Seat is located within a recess matching the pipe opening profile.
• Common water-works practice.

Concept / Approach:
Sluice (gate) valves employ a wedge-shaped circular gate that moves perpendicular to the flow to seat tightly within a recess. This provides low headloss when fully open and positive shutoff when closed. Globe valves use a conical disc against a seat for throttling, not typically in a flush recess aligned with the full-bore opening. Butterfly valves use a rotating plate and do not seat in a recess around the opening in the same manner.

Step-by-Step Solution:
Match “recess seating in the opening” to the wedge-shaped gate design → sluice valve.Eliminate spherical and parallelopiped forms which do not match standard water-works closures.Conclude with the wedge-shaped circular disc as the conventional choice.

Verification / Alternative check:
Standards for water-distribution isolation valves describe resilient-seated or metal-seated gate valves with wedge geometry to fit within body recesses.

Why Other Options Are Wrong:

• Spherical or rectangular blocks are not standard closures in distribution mains.
• Conical discs fit globe valves, primarily for throttling, not recess seating aligned with full-bore opening.
• Butterfly plates rotate on a shaft and do not use a seating recess like a gate.

Common Pitfalls:
Using globe valves for isolation in large mains leads to high losses; gate or butterfly valves are preferred for isolation.

Final Answer:
Wedge-shaped circular disc (sluice/gate valve)