Questions about testing the LWCO

Reillydog

I am looking for some guidance on testing the McDonnell-Miller LWCO series-67 on my Peerless 61-series steam boiler.

Yes – it is an old boiler that is in our family home (built in 1899). It is a one-pipe system and I believe that the boiler itself was installed in the mid-1990’s. I moved into the home after the passing of my parents and so do not have the history of how/whether the LWCO was serviced in the past. I am learning about steam heating on my own, with the help of this forum and a couple of Dan Holohan's books.

For the past couple of heating seasons I have been draining the water (till clear) out of the LWCO valve with the furnace off. I did not know that the purpose of the weekly “blow-down” was not only to remove sediment but also to test the safety cut-off feature of the LWCO.

So today I attempted to do the blow-down properly – with the furnace on with the hope of the boiler shutting off when the water reached the low level. My problem is, I do not know how much water needs to be drained to reach the level for the system to shut down. I drained enough water for the water level to drop to the bottom of the sight glass window, but the boiler did not shut off. I do not know whether it is because the LWCO failed or if I just did not drain out enough water. And I was too concerned to proceed and risk damage to the boiler (and to me).

There is no marking on the boiler itself to tell me where the minimum water level is for the boiler. There is no marking on the sight glass. And there is no information in the printed materials that came with the boiler. I would appreciate any direction that folks on the forum might be able to give me on how to proceed. Many thanks.

EBEBRATT-Ed

Usually the boiler jacket is marked, some older ones may not be. The general rule is if you can see the boiler water in the gage glass the boiler is safe to run. If you cant its not safe to run.

Normal water level is about 1/2 a glass.

If you look at the mark on the M/M#67 on the side you will see line or arrow sort of thing. That is the cutoff level.

Sounds like your cutoff needs service. What I would do is monitor the water level very closely if you don't trust the LWCO to work.

Then I would order some parts if you are going to tackle it yourself. (not that hard if your handy) or call a professional.

You can rebuild the LWCO, its kind of a nasty job. MM recommends replacement if it's 10 years old or more.

I would recommend a new control, new gage glass & washers and new gage glass valves if deteriorated

Fred

The MM-67 needs to be taken apart and scraped out. You will need a new set of gaskets when you take it apart. The gaskets are available from Supplyhouse.com or other plumbing suppliers. On the side of the MM-67, there are a series of lines cast into the housing. The top line on the MM-67 is the level that should shut the boiler down. If it doesn't, the interior walls or floor of the LWCO is likely preventing the float, inside the LWCO, to drop and shut the burner down.

Reillydog

Many thanks for your responses. I will not retest the LWCO until I can get it serviced. I do keep a keen eye on the water level in my sight glass so I feel okay for now.

I do have one more question, though, for when my LWCO is up and functioning. After doing the blow-down, which is done when the boiler is hot hot hot, do I need to shut off the boiler for awhile so that the system cools down before refilling it with water to bring it up to the proper level in the sight glass. That is, is there a danger of damaging (cracking) the hot hot hot boiler with the added cold water?

Fred

It should only take a quart to a half gallon to test and/or blow down the boiler. All that is happening is you are emptying the cavity of the LWCO. The water in the sight glass will drop but that is only because it is running into the LWCO when the blow down valve is open. When you release/close the LWCO, you will see the water in the sight glass return to almost normal. In any case, if your water fill is into the wet return or at the bottom of the boiler, as it should be, adding a half gallon of water won't hurt a hot boiler. The cold water will be tempered by the hot water in the wet return or in the boiler.