Big **** Steam Main Pitch

Owen

I have a dilemma with the steam & condensate lines at a school where I operate the boiler.

It's in an addition ('93) to an addition ('83) to an addition ('60) to the original building

(?30s), which was torn down. It's one of the smaller schools I tend, so I thought maybe I could wrap my head around the problem. At least part of the building is fairly straightforward.

Here it is: from a point 8' west of a six inch riser, the 6" steam main heads due west for 85', reduces at (thankfully) eccentric reducers from 6-4" at 85', 4-2" at 150' to a drip trap at 230'.

It drops not 11 1/2", but essentially 0". Flat for 230 feet.

I thought plumbers like the guys who put this in (I know them),

knew water runs downhill. "Like sewers, dummy. S--- runs downhill, don't it?"

But not condensate I guess. Just turn up the boiler.

Oh well, it ain't my money.

Wait a minute, it IS!

So anyway, my lament is, what the heck should I do?

12 fan/coil units on this main: approx. 3000 EDR. St. & Cond. lines are insulated. Everything is in a suspended ceiling space with some limited room.

JStar

Well...

Are there any problems with the system? Noise? Balancing issues?

Owen

Hammer

The system hammers at start up like Verdi's Anvil Chorus. That of course means bad pitch, bad traps and/or concentric reducers. I've replaced all the radiator themostatic traps and some of the F & Ts, (I tested the F & Ts when the boiler was running and marked the one's that blew steam) and now I'm concerned they may be ruined because of the pitch. Question is, what is a simple method of determining correct pitch and how the heck do I now lower everything to where it should be (or close even).

As far as balancing goes, no, it doesn't heat evenly if that's what it means.. New vents (Hoffman #75 & 40s) are on the way.

Owen

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Steamhead

One of my Dead Men's Books

says a flat main will work, as long as every runout is taken from the bottom of the main. In this way, every runout becomes a condensate drip, and you don't get enough condensate buildup to cause banging. But I've never seen this done in practice.



You have two options here. The first is to try to re-pitch the main, which will be difficult and expensive.



The second is to add drips at regular intervals to catch the condensate. This might be as simple as welding thread-o-lets to the bottom of the main and running drip lines to the return, using F&T traps if the return is dry or goes to a condensate tank.



I can't find anything on sizing the drips or how many to install. But my gut says it would be a good idea to come off the main with 3-inch pipe, to catch as much condensate as you can at each point, and reduce after a few feet or so. Maybe a drip every 50 feet along the main would work- if not, you will have plenty of room to install more.

nicholas bonham-carter

verdi's anvil

you mention hoffman 75 vents; you may need some more main venting. we have approximately 200 ft. of various 6, 5, and 2 in. mains/dry returns, and have 18 gorton #2 and 6 hoffman 75 vents. my good low pressure gauge shows 2 ounces of back-pressure, while the air is escaping. getting the air out quickly is the key to even heating, and it may help with the "chorus".

my vaporstat makes sure the pressure remains below 8 ounces coming from a 1,000,000 btu boiler feeding 55 radiators on a 1-pipe system.

if this piping started out flat, some sections may have sagged as well. i had to use a level, and tape marked with arrows to find my sags. if your hammering is strong enough you may be able to hear/feel the problem areas.

does this boiler have a "hi-lo" burner, and is it set correctly? is the boiler now over-sized?--nbc 

Owen

Drips

Hey, that's good, drips on the bottom. Yes there is a receiver tank.

The condensate line is just as bad and may have to be lowered, but I don't think it would be as difficult as the steam main.

Thanks.

Steamhead

On the condensate line

you could use a transfer pump to move the water to the main receiver tank, if needed.



Also what Nick said about venting, but fix the water hammer first. Otherwise the banging will kill the vents.

LarryC

How does the steam main deal with thermal expansion?

How does the steam main deal with thermal expansion?  Are there expansion bellows or U bends or other condensate collection points that can be tapped to remove condensate?

Owen

Pressure at the Boiler

This thing runs at over six lbs. Oh, to be able to run at two lbs. Let alone OUNCES.

My guess (I've only been here three and a half years) is that it has been this way since '93 when it was put in, and maybe before that. It will at least heat at 6# but at what cost?

I've replaced all the radiator traps, many (6) of the F & Ts (of 24), located 3 concentric reducers & replaced 1 so far. Luckily, they didn't put concentrics on the mains, these are on run-outs to F/C units. There probably are more. I hope to find and replace any that remain.

Owen

Expansion

There is no allowance for expansion that I have seen. These mains (steam &cond.) on this end of the building are a straight shot 230 feet long. I have photos I will post sometime today.

nicholas bonham-carter

6 psi system

i think the limit for most vents is under 3 psi, so your new vents may not be new for very long. is there a reason for the over-pressure?--nbc

Owen

Pressure

Simply put, knuckleheads running the show. I'm just a worker bee who happens to read this and anything else I can get my hands on. As my fearless says, "book larnin' is fine but thia is the REAL world. I thought physics worked the same everywhere but I guess not in this neck of the woods. Anyway, I haven't been allowed to experiment with it much so I don't know if if would heat lower or not. I think three pounds should be plenty.

I may go over some heads here to be allowed to try it soon. They are not running yet.

This is only one of seven I tend. Here has the worst pitch problem I've found.