Can swing check valves act as traps on two pipe dry return systems?

mstrbill

Can swing checks act as air vents or traps on some two pipe systems with dry returns?

Steamhead

In the Donnelly and Kriebel systems

radiator return elbows did have small check valves in them. But those were two systems where steam was allowed into the dry return under certain conditions. In most Vapor systems we want to keep steam out of the dry return.



Nowadays we usually run Kriebel systems as orifice systems, keeping the pressure low so steam won't get into the dry return. Not sure if that would work on a Donnelly, since I've never actually worked on one.



So the short answer is, probably not. What type of system are you working on?

mstrbill

more questions

Here is were im at , the clients house has a large one pipe system at first glance, every pipe to the 2nd and 3rd floor is a 1 pipe , and every main in the basement  is a standard circuit system gravity to end of main drip to wet return near the boiler . The 1st floor however has a mix of 2 pipe rads , very large 6 to 8 feet long , bottom piped in and out and the out to a dry return with a swing check in line and no rad . air vents. The other rads for the 1st floor are indirect metal boxed convectors with the same piping setup , with swing checks in the 2nd pipe leading to the dry return steam main and no air vent on the rad. Client says they heat up but i cant see how , and i don't understand the swing check , and i am trying to speed things up on the main with a lot of new main vents since the are only 2 now and are on a 3/8 stub . Has anyone seen these swing checks used on convectors from the 1920`s ? Or are they trap orifices in disguise ?

Steamhead

As long as the dry return is big enough

to handle steam, air and condensate, this will work. It sounds a bit like a Kriebel- maybe someone was trying to imitate that system.



Larger rads were sometimes installed as 2-pipe even when smaller ones were one-pipe, to avoid the issues with lots of condensate trying to get back down the single pipe.