Plumbing Math & Calculations

Question 1

What static pressure, in psi, does a 100-foot vertical column of water exert at its base?

Accepted Answer

43.3 psi

Answer

Each foot of water head exerts 0.433 psi, so 100 ft × 0.433 = 43.3 psi.

Question 2

A horizontal drain 40 feet long is installed at 1/4 inch per foot. What is the total fall?

Accepted Answer

10 inches

Answer

40 ft × 0.25 in/ft = 10 inches of fall.

Question 3

About how many gallons does a rectangular tank measuring 4 ft × 4 ft × 5 ft hold?

Accepted Answer

598 gallons

Answer

4 × 4 × 5 = 80 cubic feet, and 80 × 7.48 gal/ft³ ≈ 598 gallons.

Question 4

For a 45° offset with a 12-inch set, what is the approximate travel?

Accepted Answer

17 inches

Answer

For a 45° offset, travel = set × 1.414. So 12 × 1.414 ≈ 16.97, or about 17 inches.

Question 5

A pressure gauge reads 50 psi. About how many feet of head is that?

Accepted Answer

115.5 ft

Answer

1 psi equals about 2.31 feet of head, so 50 × 2.31 = 115.5 ft.

Plumbing Practice Test