Steam Piping Question

Jacob Myron_15

The quwstion about sizing the near boiler steam pipng will be answered in the instruction manual from the boiler manufacturer.

Pay attention to the chart that deals with the amount of sections for the boiler model.

For saftey sake increase the boiler header one pipe size larger than the outlet taps on the steam boiler. Never reduce te outlet tap size.

Return side of the boiler: Donot reduce the return tap of the boiler with a bushing use a nipple and an a "T". Reduce the bull of the "T" to the proper equalizing leg size which will be shown in the boier installation instructions.

Plug off the run side of the "T" with a non ferrus plug or nipple and cap. This connection may be needed in the future to clean the lower circulating passage of the boiler.

Before connecting the return piping to the boiler make sure the check valves attached to the base of the boiler return trap piping are good working condition or replace then with high quality rated check valves.

As to the velocity of steam leaving the boiler you donot have control over that because the steam piping is already in place. As long as the velocity of steam is under 40 fps the steam velocity going up the risers into the radiators will be held some where under 25 FPS, a WORST CASE SENARIO will be that steam may be audible in some pars of the house.

Follow the boiler manufactures instructions do not alter the Dunham piping near the boiler or boiler return trap and you will be O.K.


Jake

Steve_35

Near boiler piping

I'm a steam newbie and want to be as sure as I can our first job will go well. I'm going through Dan's book "The Lost Art of Steam Heating" and trying to figure out the size of the near boiler piping.

We're installing a 350K input boiler rated at 875 sq ft. It has a single 3" take off. Most of the system is a Dunham return system with an air eliminator and roiler return trap. There are a few radiators in the basement that appear to this newbie's eye to be more like a two pipe system.

I'm trying to determine what the header size should be. In Dan's book he goes over the 15fps velocity limit of older boilers. He also mentions the maximum velocity that condensate can flow against is 29fps in a 3" line. Later he mentions that modern boilers often exceed these old standards and that's why near boiler piping is so important.

It appears from my calculations the velocity with this boiler and a 3" header would be 29.6 fps. My question is does this matter if we have a two pipe system and install the equalizer with a bit of slope in the header to the equalizer?

I'm unclear just what standard I should be using in this instance. Is the 29fps for 3" pipe the maximum velocity coming off the boiler and elsewhere in the piping only if it's a single pipe system? Or is that a concern because of start up condensate on any piping arrangement?

Thanks for your time.

Steve_35

Questions

> The quwstion about sizing the near boiler steam

> pipng will be answered in the instruction manual

> from the boiler manufacturer.

>

> Pay attention to

> the chart that deals with the amount of sections

> for the boiler model.


Unfortunately the IO manual says very little about the near boiler piping other than it must run full size from the boiler and they want 24" from the top of the boiler (instead of the water line). Here's a link to the manual.
http://www.smithboiler.com/html/GB250IM-5[1].pdf

> For saftey sake increase

> the boiler header one pipe size larger than the

> outlet taps on the steam boiler. Never reduce te

> outlet tap size.


I guess what I'm looking for is the design rather than a rule of thumb. I like to know what I'm doing and why. Seems like there should be specific guidelines to follow. Maybe that's only the case in a perfect world.

Sort of like the 15fps with old boilers and keeping the velocity of the steam below certain levels on 1 pipe systems.

> Return side of the boiler:

> Donot reduce the return tap of the boiler with a

> bushing use a nipple and an a "T". Reduce the

> bull of the "T" to the proper equalizing leg size

> which will be shown in the boier installation

> instructions.

>

> Plug off the run side of the "T"

> with a non ferrus plug or nipple and cap. This

> connection may be needed in the future to clean

> the lower circulating passage of the

> boiler.


I like this idea much better than the boiler drains they suggest.

> Before connecting the return piping to

> the boiler make sure the check valves attached to

> the base of the boiler return trap piping are

> good working condition or replace then with high

> quality rated check valves.


Yes, we'll be doing this.


> As to the velocity

> of steam leaving the boiler you donot have

> control over that because the steam piping is

> already in place. As long as the velocity of

> steam is under 40 fps the steam velocity going up

> the risers into the radiators will be held some

> where under 25 FPS, a WORST CASE SENARIO will be

> that steam may be audible in some pars of the

> house.


We can't change the rest of the system but the near boiler pipe sizing will impact the velocity of the steam in the near boiler piping. If we way over size it the velocity will be low which isn't a problem other than the cost, increased startup condensation and operating heat loss. If we undersize we're going to increase the verlocity in the near boiler piping and create some problems there for sure. I'm just want to find what's the acceptable velocity in the near boiler piping in a two pipe system with an equalizer. Seems like it might be higher than the velocity in a single pipe system where the condensate has to make its way back to the boiler against the steam.

Are you saying 40fps in the riser off the boiler to the headers is okay? That's a number I like but what's the basis for it? Please remember I'm trying to learn here.

> Follow the boiler manufactures

> instructions do not alter the Dunham piping near

> the boiler or boiler return trap and you will be


I'm trying to leave the piping coming out of the return trap as alone as possible. There is a pipe that sits in the concrete a bit that's pretty rusted. We'll have to change that and I suspect the tee it's attached to. I hope to limit to that.

Thanks for the response. I really appreciate it.

Jacob Myron_16

Dunham System

I have to qualify some statements.

Wheni said leave the piping alone i meant not to alter the sizing, at the low end of thesystem make sure the heights of the piping maintains the proper distance from the boier wter line.

Typically the new boiler may have a water line lower than the existing boiler water line. In that case if a horizontal pipe located at the low ind of the return trap is 4" below the existing water line you will have to change the height of that pipe to be at 4" below the new boiler water line.

Stean velocity is calculated before the piping system is installed. The selected pipe size based on the lbs of steam per hour needed to supply steam to heat the building and the system pressure drop sets the velocity of steam to the system.

The 15 fps leaving the boiler uusually occured in old coal boilers because coal produced steam slowly. These old boilers had large outlets and larger steam header. The larger piping acted similar to a resivoir and allowed excess cubic feet of steam to accumulate in that piping.

If you look at the size of the steam mains and other steam supply piping you will find thatthe size of those pipes are pretty much the same size of the piping today used in similar systems. so the steam velocities of theat piping will not change much even with new faster steaming boilers.

The Dunham systems were not designed to operateabove 2 PSI, but the pipe size was designed to heat the building at steam pressures as low as 1/4 PSI. You will know this is a fact if you measure a radiators EDR out put. If you do this you will find that the radiators used in the old gravity vacuum sysyems are sized very similar to hot water radiators. If these radiators are used in a regular steam system or a steam system sesigned to operate at 2 PSI the rooms will be grossly overheated.

You are on the right track, you asking questions. If you need a sketch of the old dunham system you can get one from MEPCO, they have an internet site and are quite helpful with info about theold systems.

MEPCO is the old Dunham Company.


Jake