Master Plumber Exam Gas Piping Systems 2

Question 1

What is the maximum allowable pressure drop for a low-pressure gas system serving residential appliances?

Accepted Answer

0.5 inch water column

Answer

NFPA 54 allows a maximum pressure drop of 0.5 inch water column for low-pressure residential gas systems.

Question 2

Which material is NOT approved for use as a gas supply line inside a residential building?

Accepted Answer

Galvanized steel pipe

Answer

Galvanized steel pipe is not approved for interior gas piping because zinc coating can flake off and clog gas orifices.

Question 3

A gas dryer requires a shutoff valve located within how many feet of the appliance?

Accepted Answer

6 feet

Answer

The International Fuel Gas Code requires an appliance shutoff valve within 6 feet of the gas appliance it serves.

Question 4

What type of joint compound (pipe dope) is acceptable for gas piping connections?

Accepted Answer

Only compounds listed and approved for gas use

Answer

Only thread sealants specifically listed and approved for gas service should be used on gas piping joints.

Question 5

When sizing a gas lateral, which factor is NOT used in the calculation?

Accepted Answer

Color of the pipe material

Answer

Pipe sizing calculations are based on BTU demand, pipe length, and available pressure — pipe color has no bearing on capacity.

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