Arco Model K Orifice Steam System

Steamhead (in transit)

but the fix is pretty easy: disk orifices in the supply valve unions. You can get these from Tunstall, they come as blanks which you drill out to the correct size.

The key with this type of system is to keep the pressure LOW. Use a Vaporstat to keep the boiler's pressure less than 1 pound.

The F&T traps on the return risers don't belong there. Remove them.

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Jim Blum

Arco Model K

I am looking for help from someone with knowledge of Arco Model K trapless 2-pipe steam systems. I looked at a high rise apartment building yesterday that was built in 1938 and that I think originally had the Model K system, a 2-pipe steam with no steam traps on the convectors. It appears that the original orifice steam valves were replaced many years ago with regular steam valves and F&T traps were installed on the base of the condensate return risers in the basement. The cast iron convector elements still do not have traps, because of a lack of space in the cabinet I was told.

Does anyone know other high-rise buildings with systems of this type still working as originally designed?

Jim Blum

Thanks. This is a 20 story building, and my sense is that it would help get steam to the top of the building faster if I created a way to add air vents at the top of the risers.

Steamhead (in transit)

That's very doable

see page 118 of "The Lost Art of Steam Heating" for an illustration of one way to do it.

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