Steam Traps: What They Do and How to Choose the Right One

A steam system has a condensate problem by design. As steam gives up its heat at a radiator, coil, or heat exchanger, it condenses back into water, and that water needs to leave the system without letting live steam escape along with it. A steam trap is the device that makes that distinction automatically, and picking the wrong type is a common, often overlooked source of steam system inefficiency.

What a Steam Trap Actually Does

A steam trap sits at a condensate collection point and performs one specific job: open to let accumulated condensate drain out, and close to block live steam from escaping through the same path. Get that distinction wrong, a trap that's stuck open wastes steam (and the fuel cost behind it) continuously, while a trap that's stuck closed lets condensate back up into the system, causing water hammer, reduced heat transfer, and potential equipment damage.

Float-Operated Traps: Continuous, Proportional Discharge

A float-operated (lever) drain trap, like the Armstrong 1-LD line, uses a float ball connected to a lever-operated valve. As condensate accumulates, the float rises and opens the valve to drain it, closing again as the level drops. This gives continuous, modulating discharge that responds directly to the actual condensate load, rather than opening and closing in a fixed cycle. It's a common choice where condensate loads are relatively steady and continuous drainage is preferred over intermittent discharge.

Orifice Size and Pressure Rating Aren't Interchangeable

Within the same float trap body, Armstrong offers different orifice sizes (1/8", #38, 5/64", 7/64") paired with different maximum pressure ratings (121 to 300 PSIG across the line). A smaller orifice handles a given pressure differential with less condensate capacity; a larger orifice passes more flow at the same pressure but is only rated for lower maximum system pressure. Matching both the orifice size to your required condensate capacity and the pressure rating to your actual system operating pressure is the real selection decision, not just picking a trap sized to the pipe connection.

Why Trap Failure Is Easy to Miss

A steam trap failing open doesn't usually announce itself the way a leak does. Steam just quietly escapes through the open trap continuously, showing up as higher fuel consumption rather than an obvious failure symptom. On a system with many traps, a handful of failed-open units can add up to real ongoing energy waste without any single trap's failure being obvious on inspection. Periodic trap testing, listening for continuous steam flow or checking discharge temperature, catches this before it compounds over a heating season.

Matching Replacement Traps Correctly

• Match orifice size to your actual condensate load, not just the existing trap's physical connection size.
• Confirm the pressure rating against your system's actual operating pressure, since a trap rated for a lower maximum pressure than your system runs is a real failure risk, not just an undersizing issue.
• Replace on a testing schedule, not just on obvious failure, given how easy a failed-open trap is to miss without active monitoring.

National Boiler Supply carries Armstrong steam traps and drain traps across multiple orifice sizes and pressure ratings. Reach out with your system's operating pressure and condensate load and we'll help you find the right trap.