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Backflows on steam boiler fills:

icesailoricesailor Member Posts: 7,265
I recently had an inspection on a steam boiler I have been getting legal on an install by someone else.

The boiler inspector hit on something that I'm not in agreement with but I'm not arguing with him. The issue had to do with a 9D Watts bacflow preventer.

There is a standard McD-M whatever number water feeder and LWCO to feed the boiler. The original installer connected a Watts 9-11 combination hot water boiler feeder and backflow preventer. If you ran the boiler over 12# steam, it could not pass make up water. I removed the Watts 1145 F valve and left the 9D backflow. I believe that in a commercial application, the correct backflow is a Watts 009 backflow. But the inspector didn't seem all that concerned about the backflow, just that he wanted another check valve between the 9D/009 and the boiler feeder/LWCO. He claimed that the backflow could drain the water from the boiler through the intermediate vent. That means that the check in the M-M is leaking, and the one in the 009 is leaking and needs to be repaired. The backflow is installed at least 18" over the water line.

I have seen "heaters" before Watts made the 9D and 1156F's as a combo unit where some thought that the 9D went AFTER the 1156F. Perhaps some installed the 9D or 009 after the M-M feeder? That would cause them to leak.

From a plumbing standpoint, I don't understand what he was after or asking about.


  • RJRJ Member Posts: 483

       (1) Backflow             I am not sure what he is talking about, the Watts 009 back flow has 2 independent check valves, and i believe the intermediate vent is open to atmosphere. this is where the air gap fitting should go.      (2)  press, reducing valve     .   I would sometmes install a press, reducing  valve ahead of  everything if the city water press. was over 75 psig. to prevent excessive inlet press. at inlet of MM fill valve LWCO .  If the prv outlet press is set above the steam boiler press. relief valve setting you should be ok, but since the press. reducing valve is ajustable someone could change the setting than causing a problem, maybe thats what the inspector was seeing,  I also would always install a wye strainer ahead of the backflow to keep the backflow clean.
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