If street pressure is 40 psi and 12 psi is lost to friction, what is the available head in feet of water?

• A. 28 feet of head
• B. 121.52 feet of head
• C. 42 feet of head
• D. 64.68 feet of head

Answer: (D)

Pressure in psi can be expressed as feet of water head, and any friction losses reduce that available head. Start with the street pressure of 40 psi and subtract the 12 psi lost to friction to get 28 psi remaining. To convert psi to feet of water, multiply by approximately 2.31 ft per psi. So 28 psi × 2.31 ft/psi = 64.68 ft. The available head is about 64.7 feet of water, which matches the given choice. The other numbers would require different psi values than the 28 psi remaining after friction.