Traps on a two pipe system

Stewart Peiffer

I have a two pipe systems heating four units in a two story building with a total of 22 radiators. I am getting into steam engineering because one area (like the end of the line added on with three radiators does not get very much heat until hard cold of winter. I have learned that venting in number one but they also talk about traps. I done know of any traps on my system. Are they an internal part of the old radiators? Or don't all systems need them? Am I trapped without a trap?

Steamhead (in transit)

That depends

on what type of 2-pipe system you have. Some Vapor systems used water seals or check valves at the rad returns. Others used orifices on the supply valves. Like traps, these served to keep steam out of the dry return but pass air and water. The air was vented at one or more central locations in the basement.

Then there's the old "two-pipe, air-vent" system where each rad had a shutoff valve on its supply and return connections, and an air vent on the return side. In this system the returns only handle water, and the air is vented at the rads.

If you're not sure what you have, look for manufacturers' info on old rad valves, return fittings and any lumps of cast iron in the piping around the boiler. Also take pics of a couple of rads and post them here. We can help you ID your system.

"Steamhead"