CIT - Certified Irrigation Technician Hydraulics and Water Management Questions and Answers

Question 1

An irrigation system is experiencing loud banging noises in the mainline whenever a large, fast-closing electric zone valve shuts off. What is the MOST effective long-term solution to mitigate this issue?

Accepted Answer

Install a water hammer arrestor near the valve.

Answer

The banging noise is water hammer, a hydraulic shockwave caused by the abrupt stop of water flow. A water hammer arrestor is a device specifically designed with an air cushion to absorb this shockwave, protecting pipes and components.

Question 2

If the flow rate (GPM) in a given size of PVC pipe is doubled, what is the approximate effect on the friction loss per 100 feet of that pipe?

Accepted Answer

It increases by approximately four times.

Answer

Friction loss is proportional to the square of the velocity. Since doubling the flow rate in a fixed pipe size doubles the velocity, the friction loss will increase by a factor of approximately two-squared, or four times. This is a fundamental principle in hydraulics.

Question 3

To prevent excessive friction loss and the damaging effects of water hammer, what is the generally accepted maximum design velocity for water in PVC irrigation mainlines?

Accepted Answer

5 feet per second (fps)

Answer

The irrigation industry standard, recommended by organizations like the Irrigation Association and manufacturers, is to keep water velocity at or below 5 feet per second (fps). Exceeding this velocity dramatically increases friction loss and the risk of surge pressure (water hammer).

Question 4

A technician is calculating the Total Dynamic Head (TDH) for a pump application. Which of the following factors is considered part of the dynamic head calculation, but NOT the static head?

Accepted Answer

The friction loss through pipes, valves, and fittings.

Answer

Total Dynamic Head (TDH) is the sum of static head (elevation changes), operating pressure required, and all friction losses. Friction loss through pipes and fittings is a key component of the *dynamic* head because it only occurs when water is in motion. Static head exists whether the water is moving or not.

Question 5

A 25-year-old irrigation system with an unlined cast iron mainline is being evaluated. When calculating the current system's expected friction loss, what is the most important adjustment a technician should make compared to calculations for a new PVC system?

Accepted Answer

Use a lower C-Factor value in the friction loss calculations.

Answer

The Hazen-Williams C-Factor represents the smoothness of the pipe's interior. New PVC has a very high C-Factor (e.g., 150), indicating a smooth surface. Over time, materials like unlined cast iron corrode and build up scale, making the interior rougher. This increases friction and is represented by using a lower C-Factor (e.g., 100 or less).

CIT - Certified Irrigation Technician Practice Test

CIT - Certified Irrigation Technician Practice Test

CIT - Certified Irrigation Technician Hydraulics and Water Management Questions and Answers