Finding right boiler water level for one pipe steam heat system

hi all - thanx for any help ,
i have a one pipe steam heat system that is about 30 years old ...
im trying to figure out the ideal water level to keep in the boiler , my hartford loop comes back into the supply line about 6 inches above where the supply line goes into the boiler tank ... if i open the drain that is along the lowest section of the hartford loop and slowly fill the boiler until water flows steadily out of the loop drain is that a good way to figure out the highest amount of water i would want in the boiler ?
i mean - if it is overflowing into the return loop then the boiler cant get any more full right ? unless there is some hidden plumbing that i dont understand that can effect things ... ? should there always be a certain level of water in a hartford loop during the heating season ?
when i did it this way the water in the sight tube was about 1/3 of the way up the tube , so i marked it and am figuring that this is the highest i ever want to fill the boiler ...
can i safely check my low water cutoff by just cranking the thermostat and slowly draining water out of the boiler until the burner shuts down ? should it theoretically shut down before there is water reading in the sight tube ? what if the water level drops completely out of sight in the tube ? can i continue on until it shuts itself down or stop there ?
thanx for any help ...
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The line from the steam main to the water return is called the equalizer line and it should connect to the return water line about 2 inches below the lowest operating water level.

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No. There should be some markings on the boiler or the sight glass or the holder for the glass. That will indicate the minimum level the water should be. On industrial McDonald-Miller valves, it is just a line on the casting where the float is.

It is probably about the lowest. It should always be visible in the sight glass. It should not be overfilled either as you need headspace for the steam.

Yes. Open the valve rapidly to flush out any sediment when you do it. It is known as blowing down the boiler. Drain valve at the bottom should be done periodically also. I don't know what the time period is for home boilers, for industrial use, it is every shift.

It should shut down as soon as the water drops below a safe level. That is around the bottom of the glass.

SHUT IT DOWN. Never run a boiler without being able to see water in the sight glass. Never. Don't even think about it. You can do serious damage to the boiler if it fires on dry tubes.
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wrote:>

hi edwin , thanx for the response - there were marks on the sight tube but when i had the boiler tuned up last week he cleaned the tube (it was pretty stained) and now the marks are gone hehe ...
im not sure why but as my grandfather always told it before he passed on - this system has never liked it when you keep the water level in the middle of the glass .
can you explain why my theory doesnt hold ?
the return loop T's into the supply line about 6 inches above where the supply line enters the boiler ...
when im slowly filling the boiler and water starts to overflow into the return loop - doesnt that mean that the boiler is "full" ? or as full as it is going to get ?
thanx again ...
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