When changing out an old boiler

ctjomac

I have a 1953 Smith Mills boiler hooked to a counter-flow 1 pipe steam system. We will be changing it out (the boiler) as soon as the weather breaks. We are putting in a Burnham MST 396 hooked to 388 sq. feet of radiation.

We will be changing out the portion of the returns that are WET because I think it will be money well spent. We are also changing out all radiator vents and main vents.                                                                                                My questions right now (and I have a ton more than this) are:                           

The system has 2, 2" horizontal mains that run about 28 feet to the last vertical take-off, then about 32 feet of dry return before the vertical drop to wet.

Would it be smart to put some adapters on the mains after we disconnect them and pressureize them and FLUSH them out? Or is that a terrible idea?     

How do I calculate my "Main Horizontal Vents Requirement? I can put them before the wet return, but that's in 1.25" pipe. After the 2" main reaches the last rad. about 28 feet out it immediatley gets reduced as it heads back to the boiler. I prefer to put them right before it drops because I can get to it pretty easily. This applies to both mains, front and rear. Also, do tou have to "add for elbows, tees, etc.?



TThanks, Joe

Rod

Changing out an old boiler.

Hi-  Counterflow systems don't have dry returns. Do both steam mains have dry returns or is the counterflow  on just one of the mains?

I wouldn't worry about cleaning the steam mains as they generally stay pretty clean anyway being constantly "steam cleaned.". Renewing the Wet Return is a good idea as this is usually the lowest part of the system so all the gunk and crud collects here. Since the wet return is a non steam carrying pipe, you can replace it with a copper pipe if desired.

-Rod

ctjomac

Maybe my terminology is wrong...

The mains leaving the boiler header pitch with the flow of the steam about one half inch in 20 feet and after the last riser they pitch back towards the boiler at about 1 inch in 20 feet......so it seems to always be flowing with the steam.

Any idea on Main Venting sizes to get me in the ballpark (was never go in math)  

Rod

Main Vents & Megasteam

Hi- If the steam and condensate flow in the same direction, it is a parallel flow main.  The laterals going from the steam main to the radiators are an example of a counter flow as the steam and condensate flow in opposite directions.



A 2 inch pipe contains 0.023 cubic ft of air per lineal foot so 28 ft of 2 inch pipe would contains-   28 x 0.023 = 0.644  cu. ft. of air.

A Gorton #1 main vent  @ 1 ounce of pressure, has a venting capacity of .330 cu.ft. per minute so would vent your 28 foot main in about 2 minutes.



Here is a link that may be of help to you. It shows some pictures of an excellant Megasteam installation done by Steamhead and Gordo, two very experienced Baltimore steam pros.

http://www.heatinghelp.com/forum-thread/126507/Megasteam-Boiler-Install-in-July-Steamhead-Gordo

- Rod