CPD exam review

By Timothy Allinson, P.E., Murray Co., Long Beach, Calif.

Next month the American Society of Plumbing Engineers will offer its biannual CPD exam, which is an acronym for Certified in Plumbing Design. I personally never felt the need to take this particular exam (formerly known as the CIPE) because of the experience and credentials I already possess. However, it is always a good exam and credential to have under your belt to evidence your knowledge in the plumbing design industry.

Many years ago Ron George, my predecessor in this Designer’s Guide column, wrote a series of articles that consisted of CIPE review quizzes. Those quizzes were quite helpful in preparing for the exam, so I will regurgitate some of them here, complete with commentary and answers at the end of the column.

First, the following conversions and formulas should be memorized by everyone in this industry and not just for the CPD exam itself.

• psi = 0.433 x feet head
• feet head = 2.31 x psi
• (note that 0.433 = 1 / 2.31)
• BTU = heat required to raise 1 pound of water 1 deg-F.
• BTU = 8.33 5 gal. 5 deltaT
• (deltaT is the rise in temperature)
• BTUH = 8.33 5 gpm 5 60 5 deltaT
• KW = BTU / 3412
• Water weighs 8.33 # per gal.
• Water weighs 62.4 # per cu. Ft.
• There are 7.48 gal. per cu. ft.
• There are 448 gpm per CFS
• HP = gpm 5 ft. head / 3,960 5 pump eff.

In the exam you will be provided with a pamphlet of equations that you do not have to memorize, but you have to know which to use when and where.

Sample questions

1. If you were asked to estimate a preliminary plumbing budget from architectural drawings, what method would be best suited?

A. A percentage of the budget
B. Cost per fixture
C. Square foot pricing
D. A detailed material & labor take-off

(I personally think this question is subjective and that answers A, B & C could all be right.)

2. If you were asked to estimate a set of 95% plumbing construction documents, what method would be best suited?
A. A percentage of the budget
B. Cost per fixture
C. Square foot pricing
D. A detailed material & labor take-off

3. The location of the following can be determined from a new project’s civil utility survey except:

A. Sanitary sewer
B. Water main
C. Building drain
D. Storm sewer

4. Before designing a plumbing system, the engineer must determine:

A. The applicable code
B. The specification format
C. The drawing size
D. The scope of work

(Here I believe that answers A and D are both correct.)

5. What is the hydraulic radius of a 4" pipe flowing half-full?

A. 0.0625
B. 0.0833
C. 0.1040
D. 0.1250

(Hydraulic radius, Rh, is the ratio of the area of the flowing fluid over the wetted perimeter. It is measured in feet. For half-full and full flowing pipes it is the same, D/4.)

6. What is the weight per square foot of 2" of water on a roof?

A. 7.48 lbs/sf
B. 10.4 lbs/sf
C. 5.2 lbs/sf
D. 8.33 lbs/sf

7. Which has the greatest runoff coefficient?

A. Grass
B. Frozen ground
C. Loose dirt
D. Pavement

8. What is the approximate pressure exerted at the thrust block for a 6” water main at 400 gpm (5 ft/s)? This requires the Joukowsky formula:

P = WaV/144g

A. 270 psi
B. 470 psi
C. 150 psi
D. 570 psi

(You must know that W is the specific weight of water, “a” is the pressure wave speed of water or about 4,000 ft/s, V is the velocity change, and g is the gravitational acceleration.)

9. The critical velocity associated with laminar flow occurs at approximately what Reynolds number?

A. 1
B. 200
C. 2,000
D. 4,000

10. What is the neutral pH of water?

A. 1
B. 7
C. 11
D. 14

11. What are the color markings of copper pipe?

A. Type K has a green stripe
B. Type L has a blue stripe
C. Type M has a red stripe
D. All of the above

12. Which valve type is least suitable for balancing?

A. Gate
B. Globe
C. Ball
D. Butterfly

13. If you were to change a pump’s rpm from 1750 to 3500 given 20 gpm and 40 feet of head, the new flow and head would be:

A. 20 gpm at 40 feet
B. 40 gpm at 80 feet
C. 40 gpm at 160 feet
D. 60 gpm at 120 feet

14. Two parallel risers are 200' tall. One is 2" and one is 6". The pressure at the base of the 6" riser is:

A. One-third the pressure of the 2" riser
B. The same as the 2" riser
C. Three times that of the 2" riser
D. None of the above

15. Which type of copper has the thickest wall?

A. K
B. L
C. M
D. DWV

16. A 60’ tall riser reads 100 psi at its top. The pressure at the base of the riser would be:

A. 126 psi
B. 100 psi
C. 74 psi
D. 160 psi

17. Approximately how much KW is required to raise 500 gallons of water from 50 deg-F to 110 deg-F?

A. 63
B. 66
C. 73
D. 85

18. The ratio of a liquid’s density to that of water at 4 deg-C is:

A. Its viscosity
B. Its specific gravity
C. 4 to 1
D. 1.4 to 1

19. The mass of a fluid per unit volume is its:

A. Residual pressure
B. Density
C. Viscosity
D. Specific gravity

20. A 4” pipe has an invert elevation of 92.4 feet and runs 200 feet at 1/8” slope. The final invert elevation is:

A. 95.8’
B. 90.3’
C. 88.2’
D. None of the above

21. Which material is most resistant to corrosion?

A. Zinc
B. Cast iron
C. Copper
D. Steel

22. Fire sprinkler hydraulic calculations are based on which formula?

A. Manning
B. Bernoulli
C. Hazen-Williams
D. Haagen-Dazs

23. A fire sprinkler head has a k-factor of 7.6. What is the flow rate at 15 psi?

A. 24.3
B. 29.4
C. 41.3
D. 57.1

24. All valves controlling the supply of a fire sprinkler system should be:

A. Gate
B. Butterfly
C. Indicating
D. Insulated

25. The water flow in fire sprinkler system hydraulics is assumed to be:

A. Laminar
B. Tubular
C. Turbulent
D. Muddled

Answers: 1) C, 2) D, 3) C, 4) D, 5) B, 6) B, 7) D, 8) A, 9) D, 10) B, 11) D, 12) A, 13) C, 14) B, 15) A, 16) A, 17) C, 18) B, 19) B, 20) B, 21) C, 22) C, 23) B, 24) C, 25) C

Good luck to those taking the test.

Timothy Allinson is a senior professional engineer with Murray Co., Mechanical Contractors, in Long Beach, Calif.