Steam and Hydronic Systems Basics
Core concepts
Steamfitting content covers steam and hot-water heating systems that gas fitters service. Know the difference between low-pressure steam, high-pressure steam, and hydronic (forced hot water) systems, and the components unique to each: boilers, expansion tanks, air eliminators, circulators, steam traps, and pressure-reducing valves. Understand why a steam boiler needs a low-water cutoff and a safety relief valve, and how a steam trap removes condensate while holding back steam. For hydronics, know the role of the expansion tank in absorbing thermal expansion and the purpose of air removal.
Traps to watch
A classic trap is confusing a steam trap with a plumbing trap; they serve entirely different purposes. Another is assuming an expansion tank is optional on a closed hydronic loop, when it is required for safety. Questions may test whether a relief valve can be capped or valved off (it cannot) or whether the low-water cutoff is a control or a safety device. Read carefully for "steam" versus "hot water" because component answers differ.
Worked example
In a closed hydronic system, water expands as it heats. The expansion tank provides a cushion so pressure stays within the relief valve setting. Rule of thumb: a safety relief valve must never be isolated or plugged, and its discharge must be piped to a safe location.