Crossover trap

gerry gill

Ok Joe, thanks. PMJ and SWEI, answers

The Mouat system is a vapor system, it has different configurations based upon size, and also based upon vintage. The jist of it is this- the systems were very old designs. Some of the first. The inlet valve was the critical feature as the early Mouats were water seal trapped radiators, which means the 'trap' may as well not even be there, as the water seal will trap nothing, but will handle 'wisps' of steam that get that far. The steam mains, may or may not get vented at the end. The early ones had either no vent, or a vacuum waffer vent installed on the supply pipe. The return pipe had the bird cage vent which if it was a small system would be a tri-tube or a larger system would be a quad- tube..they have no moving parts and vent very well..why are they mostly gone today? good question..here is your answer.. They look really killer shined up and sitting on the end of the contractors desk..Hey they had no moving parts, it wasn't like they failed..but i digress..the systems also were vented into the chimney instead of using the bird cage vent..many are.. which way was used depended on where the return ended..if the drip was way out yonder on the other side of the basement it had a birdcage vent. If the returns all ended up back by the boiler, the return was vented into the chimney.. The Mouat birdcage vent is no longer made as the company no longer exists..but we have made them in the field.. I have even made a Mouat vacuum breaker with his tube design..Christian Egli in Dayton, (who hasn't posted in awhile) made the inlet orifices for me..did that help?

PMJ

Yes, it helps-this is interesting stuff

The Mouat radiator trap has what amounts to an internal goose neck that fills when steam is condensing. The bottom of it has a small hole that isn't big enough to empty out the neck when steam is actively condensing but will drain out a short while after there is no steam. Air can actually continue to leave the radiator when the neck is full through a small orifice above this neck.  Since there is never more than 3 ounces of pressure at the boiler and next to nothing in the radiators themselves it does prevent steam at atmospheric pressure from entering the return. But when they system has been off any time at all the neck is empty and wide open again to let air thru without any resistance on startup.The Mouat literature advertises that this "self-draining" feature will also prevent freezing. No moving parts and still working after 90 years at my place. Not bad.



Gerry, my question now is what is it about some two pipe systems that prevent them from being able to operate this way at such low pressures. If there is only one opening to the atmosphere in the entire system on the dry return and it is big enough why won't 3 ounce steam make its way everywhere like mine does? Are the supply pipes just too small? Is it just systems that have been added on to unevenly and are now unbalanced? Seems to me that pressure is definitely the enemy in the steam heating business. It sure seems that if you can hear air coming out anywhere guess what - you got pressure in that pipe slowing your steam down. Am I right?



The truth is that when I first bought this house and my engineering curiosity got the better of me there was a main vent and vents on many radiators. There was some banging and a few cold radiators. But my engineering sense led me to remove all these things. Each time I did things got better. It was only recently I discovered that where I ended up was exactly as Mouat had originally intended. As I mentioned on other threads I ended up with a solenoid valve on the dry return that I close and allow the whole thing to sink into vacuum between cycles. I am convinced that the vacuum has sped the steam even faster to the radiators on each firing and made things more even - definitely not less. But I digress too.

Steamhead

How do you

control the solenoid?

SWEI

Thank you , and yes - quite interesting!

I'm in the early stages of some new control systems for older systems that center around fully modulating burners, but I want to understand much more about what the Dead Men did before I begin tinkering.   I'm fascinated by the "dead simple, no moving parts, just keeps working" kind of stuff.  Anything we can keep, restore, or even apply to other system designs is of interest, so thanks again for your patience with us newbies.

gerry gill

most two pipe systems

were vapor, and could run at little pressure..there in lies much of the problem..the modern boilers blast steam into the system..the older ones did a better job of simmering steam into the system..the modern boiler vaporstat sucks in comparison to a damper regulator on a coal boiler or even compared to the previous old mercury vaporstats..the older the mercury switch, the more accurate..least thats been my perception..the coal boilers modulated their fire, the modern residential dont unless we add a regulator to it..balance is usually off too..if balance is off i guarantee you'll blow steam thru that water seal device..you can really balance the heck out of a system with the original Mouat valves. Attached are the original Mouat instructions if your interested.

PMJ

solenoid control

There are many HVAC ultra low pressure switches - to fractions of ounces. I have one of those plumbed just ahead of the solenoid switch and just when the vacuum is gone and the dry return would go to positive pressure it opens the valve. These two devices are also tied to a PLC which I have programmed to close the valve again immediately when the burner goes off. The pressure is so low I never hear any air coming out.

PMJ

Thanks for this/Modern Boilers

Thanks for the PDF - I am collecting Mouat documents. Do you have the cut-away view of the valve and the trap? I can post that.



My boiler is a Bryant 462,000btu input and I am guessing from the 50's. If I have to replace it one day am I going to have trouble duplicating this performance? There is a mercury vaporstat but I don't use it - it is just set to shutdown at about 1psi - not sure how I could ever reach that.



On the subject of blasting steam - for a given btu/hr output at atmospheric pressure it would seem that there isn't much you could do to change how the steam actually came out of a boiler except maybe make the header piping too small or too close to the waterline. Am I right about that?