Hydrolevel's Orginal Probe-Type Low Water Cut-Off (LWCO) Still Works Even After Almost 30 Years

[@dannywilkins887]

The bi-metalic strip, a simple but clever idea ..

[@scottk0623]

Somewhere in my minds archive I seem to remember on a fresh water fill sometimes you needed to bypass it until the water was heated for the first time. If my memory serves me I was told it was a mineral effect that caused this condition until the water was heated.

[@gordonschweizer5154]

You might be right, but it might have been to drive off the gasses dissolved in the fresh, cold water to keep bubbles thus formed from "blocking" that old-style probe? Hydrolevel was the first to come out with the probe-type LWCO. Check out the patents shown in the video & the story that McDonnel & Miller and ASME bankrupted Hydrolevel because of that. Hydrolevel took them to court and fought them all the way to the SCOTUS. And WON! Got a huge judgement and put them back in business. I'm not sure, but not long after this control came out, Honeywell came out with their "Ring Guard" electronic control. A much better control than the old control in this video, IMO. But at the time, I remember being VERY suspicious of this probe nonsense and felt a victim of sharp practice when I ordered my very first boiler with a "proper" M&M #67 and that "ring-sting" thing showed up instead. To my knowledge, that thing is still working after over 25 years.

[@scottk0623]

@@gordonschweizer5154 wow, I almost forgot the Ring Guard lol

[@gordonschweizer5154]

I still run into them now and them. I have no idea why Honeywell stopped selling them and anyb0dy that w0uld kn0wn was taken 0ut & sh0t for kn0wing t00 much. Taco briefly got into the steam LWCO game. They sent us one unsolicited to beta test back in '06 or thereabouts, we installed it for a customer as a replacement LWCO and it failed to detect the water in the boiler and shut down the burner and called for water, flooding the system. We lost that customer & Taco stopped returning our calls.

[@scottk0623]

@@gordonschweizer5154 that just wonderful🤦🏻

[@petersamios5409]

Let me see if I understand this correctly. So basically the transformer is generating a high voltage/low amperage signal that it's passing through the water in the boiler to ground. If it makes that connection, then the light stays off and all is well - resulting in continuity to the 3rd and 4th positions. If the tip is no longer in the boiler water, then the connection is broken and continuity is changed to the 3rd and 5th positions and the light is turned on to indicate the triggering of the low water cutoff.

[@gordonschweizer5154]

More or less that's it, but there is a heater circuit that runs when there is a flow of current thru the probe/boiler water. The bimetallic strip is heated and (eventually - seems to take forever) there is a make connection that allows the burner to fire. No water, no current path, heater stops heating, bimetallic strip cools and breaks circuit to burner- eventually. By today's standards, this is a total kludge, but it works and still meets Code.

[@petersamios5409]

@@gordonschweizer5154 Thanks. It seems like the bimetallic strip is the delay for the water that still may be returning - sort of like the dip switch function on the newer models (which is probably some sort of timer circuit).

[@hmedwards3]

Did you ever measure the voltage and current through the probe?

[@gordonschweizer5154]

No. I think that would vary by how clean the probe was, the water chemistry of what was in the boiler at the time, and, in still water, the build-up of gas bubbles on the probe due to electrolysis.

[@hmedwards3]

@@gordonschweizer5154 I was curious about the voltage and current required to operate the bi-metallic switch, since it doesn't use any solid state components?

[@gordonschweizer5154]

In the video, I measure the voltage to ground (or the probe) at about 148 VAC. The heater for the bimetallic strip I later measured at about 5000 ohms. Using ohm's law, we get a calculated current draw of about 0.029 amps.

[@hmedwards3]

@@gordonschweizer5154 Thanks Gordon. I was guessing the transformer was stepping up the voltage.

[@gordonschweizer5154]

You are correct. It is a step-up transformer taking 24 VAC up to 148 VAC.