Mouat Valves

HydronicGuru

This is my first Mouat System in Indianapolis, IN. This is installed in a 8600 sqft home. New boiler is only 3 years old. The last boiler removed was installed in 1993. System pipping was installed in 1926. I have done some home work on Mouat. I understand the the water seals, and how the valves work on total EDR with condensation in relation to simmering with very low vapor to act as a trap. The configuration of the home allows 3 mains. 2 which serve the home, and 1 which goes a totally different direction to a garage and huge studio room above. There are 7 radiators on the main that feeds the garage and studio. These radiators have been converted to Hoffman C-27 traps, and new Legend Angle Stem Valves. when new boiler was installed. The 5 foot tall double looped steam trap at the end of the main has been replaced with a F&P Trap. The condensate return from garage back has a Hoffman 4A. (I know Mouat did not use cross over traps, but it appears this main could have had one. There is a plug in on the supply and return in this area with no missing radiators.

The other two mains feeding the house have issues. The vents have been replaced with Hoffman 75 there are 3 total. Another company has changed several of the original handle valves that were leaking steam. (Doubt they tried to clean any springs)
The call originally came in as boiler needed flushing. I didn't take long to realize Steam was in the dry returns, and Hammering was there concern. Flushing was what they thought the solution was. I found pressretrol at 4.5 psi and no vaporstat

I know I'm on the right track. I called Marsh Company today, and they no longer make or have in stock the Series R-105 Valves. My next option would be to add traps to the radiators. That the other company has replaced valves on. This will be the only way to control steam and condensation.
Question: Assuming I add traps to radiators that do not have original valves, Will the other radiators with original Moaut valves continue to work fine considering valve will regulate steam on these radiators? Will they heat at a slower rate compared to the updated radiators with new traps and valves? Will they continue to heat the space or will these rooms be much (3-5 degrees or more) cooler?
Should I just quote to replace even the original valves now and update all the radiators?
Will there be a concern with condensate return? I assume I would have more condensate afterwards. Would this constitute a need for a false water line or a feed tank?
Is there any Mouat Salvage yards? LOL.
Any suggestions would be appreciated. Gerry, You out there?

HydronicGuru

I might add, the boiler is a Weil McClain LGB-5. The wet return is 3 inch and 42 ft long. There are a total of 37 radiators.

Steamhead

What, exactly, is a Hoffman "C-27" trap?

Post some pics. That doesn't match any trap we know of.

@gerry gill , we need you here.

mattmia2

you could use orifice plates on the radiators missing the metering valves to regulate the steam down to the amount the radiator can condense.

HydronicGuru

Steamhead
Sorry, I got carried away in my trap numbering. Standard 1/2 Hoffman 17c on the garage and studio radiators. I'll try to update with some pictures tomorrow. I am new to this site. Not many knowledgeable steam guys readily available in my area. Someone pointed me to this site. Thank you for taking time to respond.

HydronicGuru

mattmia2,
I thought about this, and read a few articles into doing so. Homeowner would love to restore rather than to update. I have a little bit of time on this, as I drained returns, and lowered pressuretrol to lowest setting. I barley even cracked the new radiator valves and left the smallest radiators off. There are (4) supplemental back up systems helping limp along right now. (Homeowner has stated they hear a little noise on startup but nothing like they were hearing, and defiantly no hammering now.)
Thank you for your response. I am sure I'll have another question or two.

SteamCoffee

Mount = LOW pressure......ounces...get a Pressuretrol....anything else is can wait....

mattmia2

SteamCoffee said:

Mount = LOW pressure......ounces...get a Pressuretrol....anything else is can wait....

vaporstat

EBEBRATT-Ed

I would think orifices might be what you need but might take some experimentation. Others that know more about vapor than I do will respond

PMJ

As you probably know already the Mouat elbow is a two speed device. It vents quickly until some condensate fills a cup so then only a smaller orifice vents through it. This clever device slows the first radiators to get steam and allows slower ones to catch up with no moving parts.

I also have a Mouat system installed in 1926. Smaller - 23 radiators. I still have all the original valves. They all hold vacuum. I have most of the original elbows. These systems will operate at very low pressure. My maximum header pressure is 2 inches of water. Also, astonishingly little venting is required. I have one main loop around the basement of the entire main house with a water seal at the far corner, and one takeoff loop that feeds the garage and former maids quarters above. I have only one vent for the entire system on the dry return in the garage. There is no venting whatsoever in the main house. Though I run in natural vacuum between burns, the system will also run fine atmospheric with just that same one vent wide open. Done it many times.

There will be plenty of installed EDR in any Mouat system. Never needs to be anywhere full. Tough to pull that off with pressure controls though. Pulsed firings yields a far better result.

Good luck with this system - one of the very best.

Jamie Hall

You certainly can add traps to the radiators with the missing regulating (Mouat) valves, but it might actually be easier to slip orifices into the unions. Some experimentation is in order there. You might also take a really close look at the outlet elbows -- if they are the original Mouat elbows, you don't need any traps. What you do need to do, if a radiator isn't heating well, is take them apart (just the union) and make sure they aren't gummed up.

The dry return -- which must be dry -- ended in the chimney. We don't do that much any more... so you will need good vents there, after they connect together but before you take a drip down to the boiler we return.

The mains do need to be vented with modern boilers. However, that can be done either with main vents or with crossover traps, if there are handy dry returns. Obviously, both the mains and the dry returns need to be dripped to wet returns -- but which end this happens at depends on which way they are pitched.

I have to admit that I'm less than keen on F&T traps on vapour systems. They aren't meant to be air vents, and don't work well as such, and you have very little pressure or elevation to play with to move condensate. If the one you mention works when you get the pressure down where it needs to be, leave it, of course -- but if not -- if you get condensate stacking before it -- take it out and figure out a way to put a crossover trap in its place, and a wet return if needed.

And yes, you need a vapourstat to control pressure. Start with it set to 6 ounces cutout and 3 ounces differential, and work from there.

HydronicGuru

Thanks for the information. I was unfamiliar with Mouat but have learned a tremendous amount. I definitely have a better understanding of vapor. The home owner has decided to update the rest of the system with new Steam valves, and traps at all radiators. I have added a Vaporstat. I have pressure set to 5 oz right now. The main portion of the home is heating well, and hammering has stopped. I have flushed returns at near boiler and water is looking good. HOWEVER! I am am still having trouble understanding what this other company has done with the takeoff loop and the retrun drip feeding the garage and old servants quarters above. Just before the end of the main the takeoff for garage and old servant quarters go out. You can see some pipes cut next to main. This appears to have been some time ago as only new pipping I see is at F&T trap. There is a condensate rise from trap with no check valve into the retrun. This area heats good but hammers bad. Some Knuckleheads' has added one pipe vents to all radiators above garage. I have plugs for these to put in tomorrow. I know there were trying to solve the same problems as I. I have some Pictures. Give me a sec.

HydronicGuru

The homeowner has informed me that the other company cut out a similar looking loop from the end of the steam main as in one just like in the attached pictures.

HydronicGuru

The 1 inch loop that goes to the floor and back up and down to wet return and vents are in the main portion of the home. I just wanted you to see what the other main looked like where it ended and went to wet return.
Thanks again guys.

Jamie Hall

That 1 inch loop is a water seal between the main and the dry return -- and, since it connects to the wet return, also functions as a drip. Splendid arrangement, and works far better than any trap ever made. Provided the pressure is kept low and the wet return really is wet -- below the boiler water line.

What it does not do is vent air from the main. If there is no crossover trap to the dry return, you're going to need a main vent.

Can you make a sketch -- with elevations -- of the piping to the garage and servants' quarters? Probably figure out what to do ;with all of us working on it from that.

PMJ

I have owned, operated, and studied a Mouat system for almost 30 years. No main vent or crossover trap is needed. Every radiator in the system is wide open to the dry return and collectively they can easily vent the necessary air from the main without ever needing any pressure at the header to do so. The original design schematic has only a dry return vent on top of the water seal where the main and the dry return join.

I have found that the biggest single factor in steam delivery time is reheating the piping. Steam just won't flow down a pipe that isn't hot enough. All the steam is consumed heating pipes back up first. And even insulated the piping cools below effective transport temperature pretty fast, as in minutes. Burner off times of even 10-15 minutes slows the delivery time due to required reheating such that all air that needs to leave the mains does so easily through the radiators at 2 inches of water at the header. It would take off times in single digit minutes maximum for the piping to remain hot enough and steam still able to move fast enough that the air not leaving fast enough was actually in the way and a problem.

I see no logical reason to ever operate these systems with the end of one burn that close to the start of another anyway; nor to run any burn long enough so as to ever fill radiators and then really need a trap.