ISA Certified Control Systems Technician (CCST) program

• March 31, 2016
• CCST

Summary

Certified Control System Technicians (CCSTs) calibrate, document, troubleshoot, and repair/replace instrumentation for systems that measure and control level, temperature, pressure, flow, and other process variables.

CCST question

A fluid is flowing through a 10-inch diameter pipe at a velocity of 6 ft/sec. When the pipe reduces to an 8-inch diameter, and all other flowing parameters remain the same, the fluid velocity becomes ________ ft/sec.

A. 2.550
B. 6.075
C. 9.375
D. 12.75

CCST Answer

The correct answer is C, 9.375 ft/sec.

Flow in a pipe can be expressed as:
Q = A x V,

where

Q = volumetric flow rate, ft³/sec
A = pipe cross-sectional area, ft²
V = fluid velocity, ft/sec

The flow rate of the fluid through the 10-inch pipe (condition 1) is the same as the flow rate through the 8-inch pipe (condition 2), so:

Q₁ = Q₂

and since Q = A x V,

A₁ x V₁ = A₂ x V₂

Solving for V₂:

V₂ = A₁ x V₁ / A₂ = [A₁ / A₂ ] x V₁

Area is proportional to the square of the pipe diameter (A = Π x D² / 4), so:

V₂ = [(10 in)² / (8 in)²] x 6 ft/sec

V₂ = 9.375 ft/sec

Reference: Goettsche, L.D. (Editor), Maintenance of Instruments and Systems, Second Edition, ISA, 2005.

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