The case of the boiler that failed on low water, this Friday's case

RayWohlfarth

In this case, an attendee at a steam seminar asked me at break about the steam boiler in his home. The cast iron boiler dry fired and cracked. The thing that was different than other cases like this was the homeowner said he blew down the boiler a few times each heating season and it still failed. Each time he blew down the boiler, the burner would shut off like it is supposed to do. It wasn't a one time event like a broken pipe that caused the boiler to fail. I'll let you know Friday at 6am EST what caused the problem.

ethicalpaul

I’m still thinking but surely the Hartford Loop should have protected it?

retiredguy

@ Ray, you did not say what low water cutoff was installed . So I am going to guess that it was one that uses a float like a McDonnell Miller #47. The lower pipe, of the 2 pipes that operate the low water cutoff, became plugged and held the boiler water in the chamber not allowing the float to drop and cutoff the boiler as it normally would and this allowed the boiler to dry fire.

archibald tuttle

@retiredguy thats plausible. although you wouldn't get much continued flow to run to clean if the lower pipe was clogged.

@ethicalpaul boiler can leak before the dry fire. doesn't explain why low water cutoff failed.

Sylvain

- I remember reading on this site something about a LWCO shuting down the burner when flushed but not when blowing down the boiler himself.
When the owner said he was blowing down the boiler, was he really blowing down the boiler or just the LWCO?

RayWohlfarth

Happy Friday All. This was when I first learned about the Evaporation Test. It simulates real life operation of the boiler and low water cutoff. The low water cutoff was a #67 float type control. It had a little bit of dirt and mud inside the chamber. It wasn't enough to stop the float from dropping when flushed but did impede it under normal operating conditions. As the boiler steamed away the water, the dirt held the float up. We are seeing more boiler insurance companies requiring this test. The video shows how I do it. It's coming to a boiler room near you.

https://youtube.com/watch?v=L17GJVvjAOw

retiredguy

This evaporation test was something I did almost every time I serviced a steam boiler regardless of it's operating pressure or BTU input. I treated the boiler as if it was a required test even if it wasn't. The only time that I did not do this test was when I knew that the low water cut off had been taken apart, cleaned and serviced as part of the yearly inspection on high pressure steam boilers that were used in industrial production or in a hospital

EBEBRATT-Ed

The 67 isn't the most easily worked on control but they are reliable unless maintenance has been neglected.

To clean them they must be taken apart and really cleaned.

Poking the float with a screwdriver or other methods is not a reliable way to get them working.

LWCOs are too important. They are as important as a safety valve or pressure control.

If you have any doubts, it will work toss it and replace it. Yes it's $$$ but what does a new boiler cost?

These controls need to be respected as they are important and not treated as a nuisance.

They may not be the best choice but, the electronic controls can fail as well. Thousands probably millions of them have been installed. I would bet the # of boiler dry fired with a 67 is pretty low compared to the # sold.

RayWohlfarth

@retiredguy You were ahead of your time my friend
@EBEBRATT-Ed The 67 is a little tough cleaning but they are workhorses.

STEAMFITTER597

Check the head! The float is attached to a bellows. The pleats of the bellows load with crud.  There is an opening to let water flow back to the bowl.  Clean and rinse the head chamber.  Also use a green scrub pad to descale the float.  The stuff comes off like egg shell.  

RayWohlfarth

@STEAMFITTER597 Sometimes the bowl is a bit challenging to clean

STEAMFITTER597

Mostly I clean the bowls with an old buck knife. Pop and scrape the scale blisters. Clean gasket face. And open drain rinse the bowl. To insure lower leg is clear by running knife down. Same with the internal head section.  

STEAMFITTER597

67s I remove the blow valve a reach up and in.  Then clean valve ball. I’d have hose will flush chamber. I remove lower gauge glass valve stem and use side rods to clear to boiler. Fill boiler and watch water flow. Never seize smear gasket faces and bowel bolts.Then button it up.  If I remember miller says 10yr life span.