Does a Two-Pipe Steam Radiator Have to Have a Steam Trap?

No, but it has to have something to keep the steam from entering the condensate return lines. That “something” may be an internal orifice, a tiny check valve you can’t see, a hidden metal ball or a water seal. There were about three dozen companies doing business between 1905 and 1930 that made these steam-stopping gizmos. They’re all out of business now. So do not remove any weird-looking device until you’ve answered three essential questions:

1. What is it?
2. What does it do?
3. What the heck happens if I take it out?

If you can’t answer those questions, put your hands in your pockets, and back slowly away from that radiator.