In pump piping practice, the nominal size of the discharge (delivery) pipe is usually selected to be how, relative to the nominal size of the suction pipe?

Introduction / Context:
Proper sizing of suction and discharge lines is essential for reliable pump operation. Suction lines are often sized more generously to minimize friction losses and avoid excessive velocity, which helps maintain NPSHa and reduce cavitation risk.

Given Data / Assumptions:

• Conventional centrifugal pump with separate suction and discharge piping.
• Goal: minimize suction-side losses and maintain adequate NPSHa.
• Typical design velocities: lower on suction, higher on discharge.

Concept / Approach:

Suction piping is commonly one size larger (or otherwise lower-velocity) than discharge. Lower suction velocity reduces head losses and entrance losses, preserving NPSH. Discharge piping can accept higher velocities because the pump has already added head and cavitation risk is negligible downstream of the impeller.

Step-by-Step Solution:

Verification / Alternative check:

Plant standards and pump installation guides recommend larger suction lines, straight runs into the pump, and minimized fittings to reduce NPSH losses; discharge lines are often sized nearer to economic velocity limits.

Why Other Options Are Wrong:

Larger or same as suction: Contradicts common practice for NPSH protection. Exactly twice: Arbitrary and not an industry rule.

Common Pitfalls:

Using identical sizes without checking velocities; adding many suction-side elbows/strainers that increase losses and reduce NPSHa.

Final Answer:

Smaller than the suction size