By George Lanthier
Part One comes from an article originally written back in 1995. We pulled it out, dusted it off and updated it to apply to today. We also included it in a book we put together for our Steam Seminar back in 2017, so we got some mileage out of it.
This article starts with an old trick that many of you guys with 30 years or more in the business may remember. As for you apprentices and rookies, hang in there, you may learn a few things, a few important things too!
As I write this, it’s the beginning of November (2014) and predictions are for another cold winter in the Northeast. In fact, right now in Buffalo, NY they are getting 70 inches of snow. It looks like it will be more “polar plunges”, “polar vortexes” and just plain nasty, cold weather. That may be good for fuel dealers, but it’s tough all around on equipment. With the nasty weather last year many service people saw a lot of steam boiler failures. Most of these were because the homeowners failed to flush the float type low-water cutoffs. One was even the failure of a boiler with a probe type cutoff, and another that had both a float and a probe! All of those failures were probably due to some bad service procedures and even worse, bad test procedures, but we’ll get to that.
Back in 1995 I originally said, “Contrary to what many believe, I like the probe and believe it is the way to go. One thing that keeps bugging me though, is that I’m not sure that all the boiler companies have them in the right place. I’m not an engineer, and don’t profess to be. I am just a service technician, but I sit there and wonder sometimes, a very dangerous thing if you know me!” As it came to pass the probe types now rule the roost today and some of the locations may still not be perfect, but that’s just my opinion.
Many years ago, numerous old-timers used the following “trick-of-the-trade” to cure the problem of people not flushing low-water cutoffs. In Figure 4-1, we see the cold-water feed in the traditional place, and in Figure 4-2 it has been moved. The trick is that whenever the consumer puts water into the boiler, the incoming feed water stirs up the muck in the low-water cutoff and helps keep the mud in suspension. Not a real cure for not flushing it, but maybe just enough in many cases to keep the boiler going until the next cleaning, at least that’s what the idea was. Since there is only one float type cutoff on the market today (1995), we ran this idea by the good folks out at McDonnell & Miller (M&M) and they said don’t do it and remember that was twenty years ago! First, it will introduce water into the bowl of the cutoff and that is against the ASME certification on the boiler. Second, McDonnell & Miller doesn’t want you to do this to their bellows in the cutoff, and so, don’t do it and I strongly recommend that if you find one of these hack jobs you get it off!
Speaking of that float bellows, in 2015 it’s worth noting that M&M states that you must inspect the float and switch mechanism every year and has since 1995. M&M goes on to state in their Publication MM-825E that a #67 low-water cutoff should be blown down weekly and inspected and tested annually. That annual inspection includes “Visually inspect the inside of the float chamber during the annual inspection. Partial disassembly may be required”. And finally, M&M recommends that the entire unit be replaced on a 10-year interval. In other words, you probably should remove it and upgrade the technology with a probe type.
Now a few questions.
Who pays for the gasket that will be needed during the annual cleaning and inspection? Who pays for the complete cutoff assembly every ten years?
Do you know how to really test a low-water cutoff?
The answer to the first and second questions is to ask if you cover low-water cutoffs under a service contract. The answer to the third question has to do with those test procedures that I’ll come back to. Now the real answer to all of these questions is, as always, education.
Education is the key and this is for my brothers and sisters, the burner techies. When you service steam boilers, do you just flush the cutoff, or do you really check them? There’s a big difference! If you just flush them, how do you know the cutoff really works? How do you flush a probe type cutoff? You must run the boiler to a point where you simulate an out of water condition and see what happens. If you don’t, you just flushed it and during the flush the burner went out. Well, a good lawyer could argue that it was just a coincidence, because it is! There is no guaranty that it really worked. Are you 100% sure all of the piping, Figure 4-3, leading into and out of the cutoff is clear? Is that brass “upper tube assembly” from the top of the cutoff back to the trim piping totally clear? It turns out that the only correct way to test a float type cutoff is the only way you can properly check a probe type, by draining the boiler with the burner running. By the way, did you note the mercury switch?
What we teach at Firedragon Academy is the following:
Do a test by lowering the boiler water level from the boiler drain valve with the burner running.
If the burner goes out at the “minimum safe level” drain the cutoff by opening its drain valve. On probe types this step isn’t required.
Shut off power to the unit.
Remove the float and switch and visually check the float and bellows. With probe types remove, clean and inspect the probe, Figure 4-4.
Replace the probe and/or the float assembly back into the boiler replacing any defective components and leave the feed valve closed.
Turn the power back on, the burner should not start.
Fill the boiler back up to its normal operating level. As the boiler reached its “minimum safe level” the burner should have restarted proving the boiler was “off on low water”.
By doing it this way you determine that it was working when you got there and was working when you were done. A great idea, since nothing beats fixing it! In addition, if it doesn’t work “as designed’ you can fix it. If we can get the customers to really flush the cutoffs weekly and we check and service the cutoffs properly yearly the boilers might just be around a while.
As long as were talking about water levels and such let me give you some more of my tricks-of-the-trade. But first, let’s see check your knowledge of things you work with every day.
Starting off, do you know the flow rates for most pipe sizes that would be used on a fresh water (potable) feed to a residential steam boiler, specifically ½” and ¾” pipe and at a working pressure of 55-60 psi?
Second, do you know the average water content of a typical four section steam boiler for oil (about 135,000 Btus)? How about the same boiler for gas? Now come a couple of dilemmas, how do you fill that boiler slowly and how do you protect the boiler from overfilling both manually and automatically? We’re going to take that up next time. See ya! l FON
George Lanthier is the owner of Firedragon Academy (www.FiredragonEnt.com), a 35-year-old Massachusetts Certified School teaching gas, oil and other heating subjects. The Academy has its training facility in Webster, Massachusetts. Lanthier is the author of more than 60 books and manuals on HVAC subjects, published by Firedragon. Lanthier is a CETP, ESCO, NATE, NORA, PMAA and PMEF Proctor and has been a Massachusetts Certified Instructor since 1975.