TL;DR
A failed-closed trap does not discharge condensate, causing waterlogging upstream. Test with an IR thermometer: the trap inlet will be cold. Isolate, clear the strainer, and replace the trap internals if the strainer is clean.
What you might see
- condensate backing up into the steam main or equipment
- equipment or pipe cold at the trap inlet
- no discharge at trap outlet even after extended operation
- upstream pipe fills with water and causes water hammer
Likely causes
Debris from scale or pipe scale plugging the trap orifice and holding the valve closed
Stuck or corroded bucket mechanism unable to open the valve
Scale or corrosion on the valve seat sealing the valve shut
Upstream piping debris plugging the inlet strainer before the trap
Required tools
- IR thermometer
- LOTO kit and isolation valves
- Heat-resistant gloves
- Strainer cleaning tool or spare screen
- Armstrong 800 repair kit (correct size and pressure class)
- Probe or stiff wire for orifice inspection
Safety first
- Waterlogged lines can produce severe water hammer when steam re-enters. Open the isolation valve slowly after repairs.
- Wear heat-resistant gloves when handling any steam system component, even when cold. Residual heat can cause burns.
Procedure
- 1
Test the trap with an IR thermometer. A failed-closed trap shows the inlet temperature much lower than the saturation temperature for the system pressure. The outlet will also be cold.[1]
- 2
Isolate the trap at the upstream isolation valve and drain the condensate.
Warning: Wear heat-resistant gloves. Even a cold-running trap has stored heat and pressure in the condensate. - 3
Inspect the Y-strainer or bucket-type strainer upstream of the trap. Remove and clean the strainer screen. A plugged strainer is the most common cause of a trap that appears failed-closed.
- 4
If the strainer is clean, open the trap cover and remove the bucket and valve assembly.[1]
- 5
Inspect the orifice for scale plugging. A probe or wire can clear a partially plugged orifice for temporary verification but does not eliminate the debris source.
- 6
Replace the trap internals with the Armstrong 800 repair kit for the correct size and pressure class.
- 7
Reassemble. Re-open the isolation valve and confirm cyclic discharge within 2-5 minutes of restoring steam to the line.
Sources
Armstrong 800 Series Inverted Bucket Steam Trap Installation and Maintenance, Armstrong International
Armstrong International 800 Series Steam Trap Installation and Maintenance Instructions, failed-closed diagnosis and strainer maintenance (general)
View source
More guides for Armstrong International 800 Series
How to diagnose a cold Armstrong 800 steam trap
A cold trap means no steam is reaching it. Check the upstream isolation valve first, then the inlet strainer. A cold trap with upstream steam and no isolation valve closed is a failed-closed trap or a plugged strainer.
How to diagnose continuous discharge on an Armstrong 800 steam trap
An Armstrong 800 inverted-bucket trap at full condensate load will discharge nearly continuously. Distinguish normal operation from a fault by checking with an ultrasonic tester: continuous high-frequency noise means steam loss; intermittent modulated noise at high rate is normal condensate discharge.
How to fix steam loss from a failed-open Armstrong 800 steam trap
A failed-open trap is blowing live steam continuously. Confirm with an ultrasonic tester, then isolate and replace the trap internals (the Armstrong 800 has a replaceable bucket module). Leaving a blown trap in service wastes significant energy.
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