Steam Boiler auto fill valve and low water cutoff

[Aristotle Zoulas]

Hello, I am new to the forum. Regarding a modern Weil Mclean steam boiler with auto fill valve and low water cutoff, I am not real sure how this is supposed to work exactly. For example, with the water level normal (just under half) I start to empty water into a bucket (to clear it out) at what point is the auto fill valve supposed to kick on a return the water to level? Is it when one gallon is removed, two gallons, etc? If I remove too much too fast, is the low water cutoff signaled first before the auto fill valve? Do the two systems work together and "talk to each other" Or are they completely independent? Also, at what point during the water removal does the low water cutoff kick on? Is it when the level in the sight glass goes to the very bottom of the glass? When the water disappears from the sight glass, does that mean that the boiler is empty or is it like a gas tank where even though you are on 'E' there is still 3-4 gallons left in the tank? Appreciate all your feedback, Aristotle

 

[Dana]

You probably have an isolating ball valve or other manual valve between the potable supply and the auto fill valve. If you turn that valve and start draining the system you should be able to detect when the low-water cutoff inhibits the boiler, even if you have the fuel supply turned off.

The low water cutoffs portion has a set of electric switch contacts mechanically coupled to a float, when the float drops too low it opens a circuit that controls the burner, so the burner won't fire. The auto fill part has a set of contacts that energize a solenoid operated valve when the level drops below the preset level. If the float or mechanical coupling to the contacts stick, neither function works. They're built to be pretty reliable, but they can and do fail. It's pretty common for them to fail such that they overfill the boiler. It's it's usually better to top off the boiler manually using the sight-glass, and let the thing operate only as a low-water cut-off. But it's also good to TEST that cut-off feature manually from time to time, to make sure it's really working.

But the system components all have part number and labels. Look up the manuals for those parts online to get a feel for how they work, and how they should (or should not) be adjusted.

Most steam boiler require regular blow-downs during the heating season to purge the accumulated grit & suspended rust particles, and keep auto-fills and level sensors from sticking. If the gunk coming out is jet-black, it's probably been awhile.