Cast Iron Steam Radiator design pressure rating

Bruce_29

I have an application reducing steam from 80 psig to 3 psig to the steam radiators. A safety valve downstream of the pressure reducing valve will be installed to protect the radiators. I have not been able to find out what the design pressure rating of a "typical" cast iron steam radiator is so I can determine what will be a safe, safety valve set pressure.

nicholas bonham-carter

All radiators and piping on a boiler-fired system would be protected by the 15 psi pressure relief valve, so presumably will stand that much pressure.
However, all these systems will function much better at a pressure in the ounces range-especially 2-pipe systems. One of the keys to proper operation is to allow the air to escape with very capacious main vents, such as the Barnes and Jones Bigmouth Mouth vent, sold in the shop here.--NBC

Jamie Hall

You need a safety relief valve set the same way as any other low pressure heating application: 15 psi. However, as @nicholas bonham-carter said, that is not the pressure you want to run at. Nor is 3 psi. That's still too high. Your pressure reducing system should drop the pressure to 1.5 psi. You may need a two stage reduction to get decent stability for that.

The radiators themselves, if they are in good condition, should take 15 psi without leaking. Older ones -- and their control valves -- very likely will not. More to the point, most thermostatic traps and vents start to get really unhappy around 3 to 5 psi.