Do you ever need to drain/clean a Hoffman Differential Loop?

Zipper13

It's been previously determined here that I have a Hoffman vapor system. The more I read up on these things the more amazed and intrigued I am at the design and ingenuity in from 100 years ago.

On the differential loop, it looks like the legs each have plugs at the bottom. I'm not planning to mess with them, but ever since I noticed them, I've been wondering if they are for maintenance and if that was expected to be part of routine upkeep when it was designed. Or maybe additional sections could be added to make a taller column?

Just curious if anyone knows their purpose.

Jamie Hall

Well... no, the differential loop doesn't need any servicing. There are no moving parts, and there really isn't any way for much in the way of crud to get in there. And what might get in there will get removed when and if the thing trips -- that is not peaceful inside the pipes!

That said, if you are feeling very brave you can try to take those plugs out. But I wouldn't bother. But don't break anything.

And on the taller column. A taller column would increase the trip pressure, and the whole idea was to keep the pressure down -- 8 ounces nominal, though most of them seem to trip at a bit less than that.

Zipper13

Interesting. I found some patent drawing cutaways of these and it looks like clear undisrupted flow would be key. So it just got me wondering . I figured over time, the legs just sit there filled with water and would be a prime place for stuff (mineral or biological) to grow and disrupt the function. But i suppose all that matters to regulate pressure is the column height - crud growing on the walls reducing the diameter wouldn't have an impact on that i guess.

I have no plans to mess with mine! As far as i know it ain't broke so why mess with it. Just curious.

Jamie Hall

When the loop trips, it goes immediately from no flow -- just a very gentle rise in one of the pipes and drop in the other -- to ejecting all the water all at once and high velocity steam going through. Tends to keep things nice and clean!

Steamhead

The drain plugs are probably there so the Loop can be drained to keep it from freezing if the building is to be unheated in cold weather.