Interesting. I think the system you are describing is a variation of a "two pipe steam" system that is not very common these days. More common systems have have an air vent, and do run on a continuous cycle.

Holohan describes the differences here: https://heatinghelp.com/systems-help-center/a-steam-heating-...

He also points out that the failure point of the system you have is that the "steam traps" tend to fail frequently and silently. The system still heats, but runs less efficiently. He says the traps typically have only a 3 year lifespan.