Diagnosing Problems with Steam Traps in Dry Cleaning and Laundry Plants

By Alan Spielvogel, Garment Care Technical Specialist

Published by the National Cleaners Association (NCA)

Understanding the Role of a Steam Trap

A steam trap is a mechanical valve that automatically removes condensate (water) from steam systems without letting live steam escape. In a properly functioning system, the trap ensures that condensate flows back to the boiler’s return tank to be reused — keeping your operation efficient, safe, and cost-effective.

Among the various types of steam traps, the inverted bucket trap is the most common in dry cleaning and laundry plants.

How an Inverted Bucket Trap Works

Inside the trap, a small inverted bucket (float) rises and falls as steam and water flow through it:

When steam enters, the bucket floats, closing the valve and preventing live steam from escaping.

When condensate enters, the bucket sinks, opening the valve and allowing condensate to discharge.

This constant balance maintains proper steam flow and protects your boiler system from water buildup.

Common Steam Trap Problems

1. Float Stuck in the Open Position

When the float is stuck open, live steam escapes back to the boiler.

Result:

The boiler’s condensate pump can’t refill the boiler properly.

Low-water safety cutoffs may trigger automatic shutdowns.

2. Float Stuck in the Closed Position

If the float is stuck closed, steam becomes “wet” and loses efficiency.

Result:

Machines that depend on dry steam — such as presses or form finishers — may malfunction or deliver inconsistent results.

How to Test a Steam Trap

Before testing, make sure the boiler is under full operating pressure. Then use one of the following methods:

1. Broomstick or Stethoscope Test

Tap or listen near the top middle section of the trap.

A healthy trap will “click.”

A “whooshing” sound means the float is stuck open.

2. Trap Crayon or Tape Test

Apply temperature-sensitive crayons or tape to both the inlet and outlet.

If it melts only on the inlet, the trap is functioning.

If it melts on both sides (or not at all), the trap is defective.

3. Laser Temperature Test

Aim a laser thermometer at the inlet and outlet.

The inlet should be 10–20°F hotter than the outlet.

Equal readings mean live steam is blowing through a failed trap.

4. Cold Trap Check

If the trap is cold to the touch, it may have a clogged strainer or a failed float — both require repair or replacement.

Don’t Forget the Check Valve

When replacing a steam trap, also replace the check valve located near the outlet.

Purpose:

Allows condensate to flow toward the boiler

Prevents condensate from flowing backward into the trap

A defective check valve can mimic a failed steam trap — replacing both ensures system reliability and prevents misdiagnosis.

Key Takeaways for Plant Operators

Inspect steam traps regularly to maintain efficiency.

Replace defective traps and check valves immediately.

Properly functioning traps reduce downtime, energy waste, and repair costs.

About the Author

Alan Spielvogel is the NCA’s long-time technical specialist, providing decades of expertise in garment care operations, plant maintenance, and energy efficiency.