Journeyman Plumber ExamFixtures, Faucets, and Other AppliancesHard
A plumber is installing a new gas-fired clothes dryer in a residential laundry room. The dryer requires a 1/2-inch (DN15) gas supply line. The total developed length of the gas piping from the main manifold to the dryer connection point is 30 feet (9 meters), and there are six 90-degree elbows in the run. Assuming natural gas with a specific gravity of 0.60 and a pressure drop of 0.5 inches water column, what is the equivalent length (in feet) of the piping for sizing purposes?
- A60 feet
- B54 feet
- C30 feet
- D42 feet
Show answer & explanationAnswer & explanation
Correct answer: B. 54 feet
To calculate the equivalent length, you add the developed length to the equivalent length of fittings. For 1/2-inch gas pipe, a 90-degree elbow is typically equivalent to 4 feet of straight pipe. Therefore, 30 feet (developed length) + (6 elbows x 4 feet/elbow) = 30 + 24 = 54 feet.
Why the other options are wrong
- A. This would be if elbows were 5 feet equivalent, which is too high for this pipe size.
- C. This only accounts for the developed length, ignoring fittings.
- D. This would be if elbows were 2 feet equivalent, which is incorrect for this pipe size.
Equivalent Length (Gas Piping)
The sum of the actual developed length of gas piping and the equivalent length of all fittings (elbows, tees, valves) in the run, used for accurate pipe sizing.
- Fittings create friction loss, reducing gas flow.
- Equivalent length tables provide values for various fittings and pipe sizes.
- Crucial for ensuring adequate gas pressure and volume to appliances.
Memory trick: Think of fittings as 'extra pipe' that adds to the total length for sizing.