FE Civil Practice Question Solution included after investigation
CASE E-049 · FE

The Faster Pipe Section That Lost 16 kPa of Pressure

The pipe stayed level. Velocity increased from 2 to 6 m/s, and pressure fell from 300 to 284 kPa.

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Case E-049 engineering failure visual
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4

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Case Brief

SAME PRINCIPLES. HIGHER STANDARDS.
PROBLEM STATEMENT

Water flows through a horizontal pipe that contracts. Upstream velocity is 2 m/s at 300 kPa gauge; downstream velocity is 6 m/s. Neglecting losses, a note predicts pressure remains 300 kPa because elevation is unchanged. Calculate the downstream pressure and diagnose the energy-balance error.

Fluid Mechanics Hydraulics Civil Design Verification Root Cause Analysis Safe Correction
E-049
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CASE CLOSED · ENGINEERING VERDICT

What actually failed — and what should change.

What failed

Pressure was assumed constant solely because the pipe was horizontal.

What was missed

Velocity head increased through the contraction.

Corrected model

Balance pressure, elevation, and velocity terms with Bernoulli under the stated assumptions.

QUICK ANSWER

For lossless horizontal water flow, p1+0.5rhoV1²=p2+0.5rhoV2². With p1=300 kPa, V1=2 m/s, and V2=6 m/s, the pressure drops by 16 kPa, giving p2≈284 kPa gauge.

ENGINEERING TAKEAWAY

Bernoulli balances pressure, elevation, and kinetic energy. In a horizontal contraction, higher velocity can be accompanied by lower static pressure.

CASE QUESTIONS

Questions this case should settle.

Does pressure stay constant in a horizontal pipe?

Not necessarily. If velocity changes, Bernoulli predicts a corresponding pressure-head change under idealized conditions.

What pressure results when water accelerates from 2 to 6 m/s starting at 300 kPa?

About 284 kPa gauge when elevation is unchanged and losses are neglected.

NEXT FE PRACTICE QUESTION

The Channel That Carried 5.69 Cubic Meters per Second

Fluid Mechanics Hydraulics · 5–10 min

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