Heavily Modified Mouat

MattinIndy

Hello all,

Looked at what is left of a Mouat System today. It has a lot of issues and looking for some input from you all. Honestly, not sure we are even going to bid this job because of it.

On arrival the first thing that got my attention was the vent from the condensate pump is actually piped OUTSIDE! I asked the homeowner if they see steam coming out of that and they said it is so heavy at times its hard to use the entrance on that side of the home. Its been like that for years, and yes the boiler is rotted out.

One of the steam mains has an F/T at the end of it, the other does not. They both tie into dry returns and make their way to the condensate pump. The pressure-trols are cranked to the max as well... Just as you'd guess.

I want to eliminate the condensate pump completely. My question is, if I drip the dry returns down to the floor making them wet returns before getting to the boiler is that a viable option? There is a Hoffman #75 main vent at the end of both mains before they go there respective dry returns.

I have other info I can add, I just didn't want to add too much and muddy the waters even more.

Steamhead

Where are you located?

@gerry gill is our resident Mouat expert................

Mad Dog_2

Sounds like an awesome Steam Challenge. Its almost always less costly to rebuild whats there.  You have to weigh how deep in to this do I want to take this?  Will the owner appreciate your efforts? Give a bid with separate options  Replace boiler only (So you are not way out of whack with the Low baller knuckleheads) and then system problems are a separate line item.  

If you can post some good pictures, we will all get you through this.   Mad Dog 🐕 

MattinIndy

Here's some pics. I am located in Indianapolis. Just so we all are on the same page. No work done here was done by the company I work for. As you'll see the flue/chimney is unlined and wrong on a few levels. The first step is he is having that corrected by others.

In the pics showing the wall behind the boiler those are the two dry returns coming in about 4 feet off the ground from both directions. They tee together on the wall directly behind the MM47-2. I'm wanting to get rid of the condensate pump and drop both of those dry returns down below the water line.

Steamhead

If those are dry returns from the radiators, they need to be vented. If they tee together and then slope down to the condensate tank, that's how they vent. You'd need to add big main vents (as Gorton #2) to them, up near the ceiling.

Are the steam mains vented?

And is the boiler header welded rather than using threaded joints?

MattinIndy

@Steamhead. There is a vent at the end of each main. Currently they are Hoffman 75's, we will be changing those to Gorton #2's. Also, The header is threaded. We don't weld pipe so we will actually be removing all of the welded pipe as we are going to be quoting a substantially smaller boiler and it will be too hard to reuse any of that header.

PMJ

@MattinIndy,

In the for what it is worth department:

I have a 1000 EDR Mouat system 95% as original and still running the boiler that replaced the original coal fired one. I have been the owner/operator of this system for 30 years.

I removed both the main and dry return vents inside the house about 20 years ago. I have only one vent on the dry return from a garage radiator with a solenoid check valve. So, there are no vents whatsoever inside the main house. I let the entire system go into vacuum between burns. Steam distribution is very even and dead silent. There is no exchange of air from inside the steam system and the living space at all. The amount of venting these systems need is negligible if you simply just don't let the air right back in every burn that you just removed. The location of the lone vent proved to be unimportant as well. I use the solenoid vent so as to be able to start venting right when the system returns to positive pressure on each new burn, so that whatever air pushing is required can all take place at a pressure below the cracking pressure of a manual valve. There is never enough air at any time coming out of this single solenoid operated vent to make a sound, and it is just a 1/2" npt valve.

Steam main and dry returns loop around the main house with one loop off to the garage and maids quarter rooms above. The loops in the main house drop down into a water loop in the far corner away from the boiler and the wet return runs from there back to the boiler.

I run with a custom PLC control on this system but it is still better vented this way with the PLC bypassed using a permanently installed backup manual check valve at the same location in the garage and the vaporstat control that came with the house, though pressure will never get high enough to trip it.

MattinIndy

@PMJ Very interesting! One thing with the system I'm looking at that probably makes a big difference is all of the radiator traps have been changed to Hoffman 17C's.

I'm not familiar with the vent set up you are describing. Is the "solenoid" on the vent check valve controlled electrically?

PMJ

MattinIndy said:

@PMJ Very interesting! One thing with the system I'm looking at that probably makes a big difference is all of the radiator traps have been changed to Hoffman 17C's.

I'm not familiar with the vent set up you are describing. Is the "solenoid" on the vent check valve controlled electrically?

In my opinion these systems should be controlled by a method (there are many possible ways) whereby the boiler can never run long enough under any circumstances to fill radiators to the point where traps are necessary. That is how I run mine. Once that is established by the control radiator traps are no longer needed and your Hoffman's would simply remain open at all times. The system then becomes just one big open pipe without any devices anywhere to separate any section from any other, and vacuum can form and improve steam flow without causing any other issues.

Yes, it is an electric solenoid and is itself the check valve. It closes when the burner turns off and vacuum forms. On the next burn when steam refills the system to the point it was at the end of the last burn the system pressure then goes a couple inches water above atmospheric and the very small amount of air that leaked back in during the vacuum phase is pushed out.