Main bottleneck

Patrick_North

Hello all,





It’s the continuing saga of a poorly piped church boiler.

Boiler is piped to service two buildings- this is controlled via zone valves. Large

(small commercial) steam boiler utilizes only one tapping, takeoffs from the

header are horizontal, and the equalizer is a bit undersized. In other words-

it throws up a lot of water into the mains (one for each building).





This problem is especially bad for the one takeoff:





(see "Before")







The “header” (far right- looking down the pipe) is 4” and then reduces

to 2 ½” for the horizontal takeoff to the main. It is further throttled down to 1 ¼” for

the sake of the zone valve. I understand they’re not cheap in larger sizes.

Sigh. This main rises another 10” or so and then maintains that level (plus adequate

pitch) until its end. This main is counterflow with a drip before the takeoff

to the first radiator on the main.





As you can imagine, it seems this bottleneck is quickly

overwhelmed with boiler water, and the layout holds back a sizable puddle

(after the zone valve). The boiler cycles on pressure and takes quite a while

to heat all the rads (sorry, I haven’t timed it).





The boiler is in OK working order, yet it’s

definitely in its golden years so a full repipe is not in the cards/budget. I’m

hoping a more modest fix can improve things substantially. What do you think

about this:





(see "after")







Basically, cut out the 1 ¼” pipe and replace with full size

2 ½”. Add a drip to keep the line free of quite so much boiler water. While I’m

wary of zone valves on steam (especially in a case like this that was so

obviously hacked) the church happens to have a 2 ½” zone valve body we could

have swapped in essentially for “free.” If it proves unnecessary we can disable

it, but we wouldn’t want to have the piping redone to add it back. I also don’t

like having the valve on the horizontal and wonder if it could/should be put on

the somewhat vertical bit where the main rises 10” or so.





 





Thoughts?





Thanks,





Patrick

Patrick_North

PS...

Though now that I think about, we could probably do something like this with not much more expense (see picture).

Patrick

Unknown

drawings on paper will

Drawings on paper will always work better... make senses, I would install drip leg with f/t trap after the valve til budget allows for proper replacment. Got any pictures of the system?

Patrick_North

No pix

No pictures at the moment, though I could go and take some. It's such a hot mess I thought a diagram would be a lot easier to "see."



As for the trap, I hadn't gotten this far in my thinking about what work to ask for. Having not thought about it, I didn't think we'd need one and assumed we'd tie the drip right into the wet return. What is the purpose in this context?

Thanks,

Patrick

Unknown

needs to go back

Into my steam fitter and drawing books.. yes, you may drip it to the wet return if the system pressure is in ozs.. other real steam pros will chimed here soon..

JStar

Steam

Stick with the 2nd picture in your first post.



Think about it...in the 3rd picture, what is going to happen to the water when the valve closes? It'll build up and slam right into the valve causing MASSIVE water hammer. All drips need to be before the valves.



It's acceptable to drip into a wet return as long as there is enough A Dimension from the water line to the drip fitting in the main.

Jamie Hall

Definitely the second picture

in the first post.  You are going to see a WORLD of difference.  You won't believe the difference it will make!  The type of throttling you have in there now is a real no-no with saturated steam; even if the boiler were piped perfectly you would still have a lot of condensate just beyond that teeny-weeny valve and not a whole lot of steam.  (I learned that the hard way, trust me).



You are fortunate to have the larger valve hanging around... they are expensive.



The valve on the horizontal won't be a problem if you put in the drip you have shown.

Patrick_North

More info

The second layout it is, then, thanks gents!

I imagine this will be cheaper for us as it leaves more piping intact, but I have to say I don't understand the problem with the third scenario, Joe. Can you give me a little more info, just out of curiosity?

When that zone valve closes steam will leave the header for the second main (not shown in my diagram). Whatever water gets thrown up into the left side would be free to go straight through, past the T (with valve at the top) and on to the drip.

And I don't see how the drip is before the valve in my second picture- I'd call that "after" given the flow of steam from the boiler?

My "logic" for the third layout was that a vertical takeoff would leave more water behind. But clearly I'm not understanding something right in front of my face.

Thanks for the help!

Patrick

JStar

Steam

I made one assumption, that the steam is moving from left to right. Is that correct?

Patrick_North

Aha!

No- in my drawing steam would be moving right to left. Sorry for the confusion- is #2 not ideal now?

Thanks,

Patrick

JStar

Steam

Neither. In #3 condensate can still settle on top of the one valve when it closes.

Jamie Hall

I did assume right to left, Patrick

and I'm still happy with your number 2 in the first post.  The real key to it is the drip on the downstream (left hand) side of the valve -- that is critical, both when the valve is open (there will be a little condensation, even with a full port valve) and even more when the valve is closed, to get rid of any condensate which might collect then and create problems when the valve opens again.