Plumbing Principles Relevant to Gas Work
Core concepts
Gas fitters frequently work alongside plumbing, and the exam checks your grasp of water supply and drainage basics. Understand pipe materials (copper, PEX, galvanized steel, PVC/ABS), their pressure and temperature limits, and where each is permitted. Know the purpose of traps, vents, and cleanouts, and how a trap seal prevents sewer gas from entering a building. Water hammer, thermal expansion, backflow prevention, and the difference between a pressure-reducing valve and a check valve are common topics. You should also know how to protect gas piping from contact with water piping and from corrosion.
Traps candidates miss
One frequent trap is assuming any plastic pipe can carry hot water; only rated materials may. Another is confusing a vent (which protects the trap seal) with a drain. Questions may ask about the minimum trap seal depth or about bonding requirements when metallic water and gas piping are present. Watch for wording about "potable" versus "non-potable" and about backflow devices on boiler feed lines.
Worked example
A fixture drain requires a trap with an adequate water seal to block sewer gas. Rule of thumb: a trap seal must be deep enough to resist evaporation and pressure fluctuations, and every trap must be vented to prevent siphonage. When gas piping runs near water piping, maintain separation and protect against contact corrosion.