Dunham Vapor-Vacuum System

Kevin Hay

Dan:

I looked at job last week with a Dunham Vapor-Vacuum System. It has (Qty-19) Dunham #1-A steam traps, Dunham #9-A return traps, and a Dunham Type #220 air vent. One 3" Steam Supply splitting into (2) 2-1/2" mains at the north side of the house and (2) 1" dry returns tying together into one 1-1/4" dry return at the south side of the house. It is piped exactly like figure 12 on page 237 of your Lost Art of Steam Heating Book, except it has two steam mains terminating into the return main through thermostatic traps and both 1" dry return mains tee together at the south side of the house into a 1-1/4" dry return main before making its way back to the boiler in the center of the house. All end of the mains are about 76" AFF near the boiler.

The house was built about 80-years ago, and the existing boiler was replaced about 40-years ago, of course the (2) check valves were not lowered at that time in relationship to the new water level line, and they have a standard Honeywell PA404 pressuretrol controlling the pressure way too high, about 5-PSI.

The existing return trap is banging loudly (big time water hammer), especially when the owner raises the thermostat from 60°F to 70°F in the morning, probably a cold start. This got a lot worse when the contractor cleaned the soot out of the leaking boiler a couple of weeks ago. I am guessing he raised the steam pressure at that time, as well as the Dimension "B". Since the system was hot, I was not able to check the crossover traps for proper operation. I have already shipped the new 250 Mbh boiler, with a Honeywell L408A Vaporstat --- should the contractor put it on the old boiler first, set it at 8 oz and see if the banging goes away???

While replacing the leaking boiler they also want to replace the return trap and vent and go back in with a standard two-pipe system by adding (2) F&T's, one on each end of steam main, and a main vent on the dry return. It looks like the piping was sized for 1/2 ~ 2/3 oz pressure drop per 100' pipe. This is a small two-story house with about a 625 EDR load, about 300 EDR on one return and 325 EDR on the other return. You explain in your book to use a boiler feed system, but can't we use the F&T's and main vents since the end of all mains are 76" AFF and the new boilers normal water level line will be 24" AFF?

p.s. Any problem with putting on some thermostatic radiator valves on the 2nd floor radiation, which they do not use except when kids come by to visit grandma for the holidays?

Kevin Hay

Dunham Vapor-Vacuum System

Dan:

I looked at job last week with a Dunham Vapor-Vacuum System. It has (Qty-19) Dunham #1-A steam traps, Dunham #9-A return traps, and a Dunham Type #220 air vent. One 3" Steam Supply splitting into (2) 2-1/2" mains at the north side of the house and (2) 1" dry returns tying together into one 1-1/4" dry return at the south side of the house. It is piped exactly like figure 12 on page 237 of your Lost Art of Steam Heating Book, except it has two steam mains terminating into the return main through thermostatic traps and both 1" dry return mains tee together at the south side of the house into a 1-1/4" dry return main before making its way back to the boiler in the center of the house. All end of the mains are about 76" AFF near the boiler.

The house was built about 80-years ago, and the existing boiler was replaced about 40-years ago, of course the (2) check valves were not lowered at that time in relationship to the new water level line, and they have a standard Honeywell PA404 pressuretrol controlling the pressure way too high, about 5-PSI.

The existing return trap is banging loudly (big time water hammer), especially when the owner raises the thermostat from 60°F to 70°F in the morning, probably a cold start. This got a lot worse when the contractor cleaned the soot out of the leaking boiler a couple of weeks ago. I am guessing he raised the steam pressure at that time, as well as the Dimension "B". Since the system was hot, I was not able to check the crossover traps for proper operation. I have already shipped the new 250 Mbh boiler, with a Honeywell L408A Vaporstat --- should the contractor put it on the old boiler first, set it at 8 oz and see if the banging goes away???

While replacing the leaking boiler they also want to replace the return trap and vent and go back in with a standard two-pipe system by adding (2) F&T's, one on each end of steam main, and a main vent on the dry return. It looks like the piping was sized for 1/2 ~ 2/3 oz pressure drop per 100' pipe. This is a small two-story house with about a 625 EDR load, about 300 EDR on one return and 325 EDR on the other return. You explain in your book to use a boiler feed system, but can't we use the F&T's and main vents since the end of all mains are 76" AFF and the new boilers normal water level line will be 24" AFF?

p.s. Any problem with putting on some thermostatic radiator valves on the 2nd floor radiation, which they do not use except when kids come by to visit grandma for the holidays?

Steamhead

No Need to remove the Return Trap

or use a boiler-feed pump on that system.

Banging is caused by water and steam meeting up where they shouldn't. If the Return Trap is banging, you probably have steam leaking into the dry return thru a bad radiator or crossover trap someplace. Find the leak and fix it.

If the Return Trap really is malfunctioning, Tunstall can rebuild it. They can also replace the innards of the rad shutoffs to make them into TRVs. Tunstall also makes replacement trap innards, Barnes & Jones does too.

The Return Trap was designed in an era when it wasn't possible to control boiler pressure within a few ounces. With a Vaporstat on the job, the Return Trap then becomes a backup safety device. This is akin to wearing both a belt and suspenders- nothing wrong with it.

The Dead Men who designed that Dunham system were geniuses. It will work best- and run rings around almost any modern system- if it is kept in its original configuration, or as close to it as possible.

Web sites:

www.tunstall-inc.com

www.barnesandjones.com

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