Steam & Excursion > Purpose of a steam engine doing a "blow off"?

Greetings, as George and I look forward to releasing the programs from our Colorado steam trip, we want to make sure we provide accurate information on each railroad. I have a idea, but what is the purpose of a steam engine performing a "blow off", where a steady plume of steam is released from the bottom? Is this excess moisture that builds up in tanks and needs to be released? For example, on the Durango & Silverton, they do this in the yard, and again at Highbridge, and departing Silverton. Thank you for your help!

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Chris Bogley
Bowie, MD

I've heard of a blow down, never a blow off...

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SVTS Wrote:
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> Greetings, as George and I look forward to
> releasing the programs from our Colorado steam
> trip, we want to make sure we provide accurate
> information on each railroad. I have a idea, but
> what is the purpose of a steam engine performing a
> "blow off", where a steady plume of steam is
> released from the bottom? Is this excess moisture
> that builds up in tanks and needs to be released?
> For example, on the Durango & Silverton, they do
> this in the yard, and again at Highbridge, and
> departing Silverton. Thank you for your help!

More correct terminology is "Blowdown", where the left and right blowdown cocks, located at the lowest portion of the firebox sides (mud ring), are opened up in order to blow out  mineral sediments in the boiler water. Addition of various chemicals in the tender water is designed to keep the sediments (mud, etc.) from sticking to the internal steel components of the firebox/boiler. On a regular basis, those "settled" sediments need to blown out at safe locations on the railroad. Thus, the locomotives are being "blown down".

I just "blew off" a telemarketer, does that count?

Out

Once again, with feeling:

Put a pot of water on your stove in the morning and bring
it to a boil.

Boil it all day long, adding water when necessary.  You will
have to add water pretty frequently.

After about 6 hours, take the pot off the stove and dump the
water out.  Now look at what is stuck to the inside of the pan.
That is concentrated minerals that are always in water.

Now, figure you probably only boiled away 5 or 10 gallons
of water.  Then imagine what the inside of that pot would look
like if you had boiled away 10,000 or 20,000 gallons of water
or even more in that same time frame.

THAT'S why you do frequent locomotive boiler blowdowns.

callum_out Wrote:
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> I just "blew off" a telemarketer, does that
> count?

No. But I will give you one Attaboy.

Cheers,
Jack

Re Chris Bogley's ...

Chris, 
Thanks for your inquiry.
"Hotwater" gave a very accurate and succinct reply.  I like his direct approach to steamers.

Some distinctions between water  treatments between stationary boilers and RR boilers are in order....
Years ago, steam designers ( boiler engineers) learned the hard way ( no pun intended) about naturally occurring minerals,gasses and minute creatures in various streams, wells and rivers.

These sediments vary in quality as well as in quantity.  Boiling thousands of gallons of water concentrates these sediments ....
eventually affecting both the heat conduction, away from the hot boiler steels, [ sediment accumulation really reduces heat transfer inton the water & engines are then slow to make steam] as well as prompting violent frothing and foaming of the boiler water.  Sometimes, the impurities coalesce on the surface of the boiler water and form a weighty mass of foam bubbles.
That often results in affecting the apparently 'clear' water in the boiler's sight glasses ---- the weight of the foam raises the water in the sight glass AND. Fools the crew into thinking that the y have plenty of water in the boiler......but sometimes the water level in the boiler is dangerously LOW, setting up conditions that can result in boiler 'disastrous events', as often happened in the old days.

[Sometimes these lessons are forgotten, mitigated by zealous chemical salesmen and ignored by inexperienced locomotive maintainers.   Mistreating your boiler is a hard way to learn some very basic habits.  Many folks fail to learn as they are around these things.  Smart people ask questions ----- that are very basic to engine care and feeding. 
Un-smart people ask no questions, they already know-it-all.  They insist on learning their "teaching moments" the hard way....]

The sight glasses are small windows of very strong glass that allow the boiler operators to see how much water is in the safe operating zone ----- showing the proper depth of water needed for safe operation.

Using distilled water, as in cooled boiler condensate,  in boilers elininates all the impurities from the water, thus no sediments and no foaming, and no bad effects of corrosive chemicals, and no bad effects from 'electrolysis' brought about by electrical conduction currents inside the boilers.

Stationary engineers continuously recycle the condensed exhaust steam from the engine cylinders,  or turbine.  By constantly recycling the boiler water, the pure water (condensate) keeps the boiler clean and happy.  Stationary boilers DO require the continuous addition of small amounts of 'make-up' water to to the boiler feedwater system.

The make-up water is treated with sediment-precipitating agents and biological trapping mechanisms all aimed at eliminating the kinds of things that become heavily concentrated, over time.  When properly treated in this way the water is physically very smooth and slippery to the touch....ergo: ' softened' water.

One of the more deleterious substances ( to boilers) is the air and its oxygen that are absorbed into the water. Often this gas release occurs inside the boiler and together with the high heat, the oxygen eats away at all the metal ( particularly) iron-bearing  steels.
Oxygen action is VERY bad on the boiler insides.  Many methods, chemical as well as 'mechanical' means, are used to bubble of the dissolved air and oxygen ---before it enters the stationary boiler plants. Open type of feedwater heating/pumping systems often use a medium pressure spray, through a restrivpcting nozzle, the sudden pressure drop readily releases the gasses and they're vented in front of the stack..

Railroad boilers have no such luxury.  The boiler water may get tiny amounts of sediment-enhancing chemicals added to the boiler feedwater. But soon the addition of too many chemicals simply becomes more sediment to have to get rid-of. Rather than condensing the exhaust steam, the used sream from the cylinders is used to draft the fire ---- thus producing fire heat to match the "load" on the engine.   The greater the load, the hotter the firebed, and the more steam is produced...

Being 'sedimentary' these chemicals tend to collect at the bottoms of loc boilers.  That sedimentation period is a long time, so after quietly sizzling at night, it's wise to blow out the mud and sediments early in the mornings.  Blowing down materially lowers the water level, so fresh water from the tender is added to the boiler.  This tends to dilute the concentrations in the boilers and promotes enjoyable trip experiences by the crew in the cab.

So, over time loco boilers were kept the cleanest by the folks that knew the composition of water impurities in their territories, and the engine crews and roundhouse boys made blowing-down a regular routine,  largely based the problems contained in the local water supplies.

An old RR adage was " Never put anything into an engine's boiler that you would NOT drink, yourself!"

So recognize that very beneficial practice and remind yourself that THAT engine crew "knows their STUFF".

Thank you for your inquiry, keep up your interest. Become knowledgable in various locomotives' blow down piping and blowdown apparatus,  and notice blow down 'timing' --- as well as where the cylcles are performed.

Wes, in Fairfax.



Edited 2 time(s). Last edit at 08/12/16 16:30 by wcamp1472.

Which is why the ATSF was one of the first railroads to go to diesels... The water here in Mojave and other desert towns has lots of calcium.

Bill Deaver
Tehachapi, CA

My simple answer:  The water put in the boiler has many impurities, but the steam that leaves is 100% pure water, so minerals, dirt, etc. accumulate and must be removed.   

callum_out Wrote:
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> I just "blew off" a telemarketer, does that
> count?
>
> Out

Only  counts if you engulfed him in live steam (hoping, hoping, please?)

When you ride these trains enough you will find that the crews have their favorite spots to blow down the engine. One such spot is the bridge at the north end of the High Line on the Durango & Silverton. The throttle of the engine is closed as there was no need to work steam for the previous 2 miles. The gunk settles and when the engine is on the bridge out it goes.
​  Tanglefoot Curve on the Cumbres & Toltec is another spot as is the bridge at the Lebannon Mine stop at the Georgetown Loop. On my 1998 cab ride we stopped on the bridge and fireman John Hammond decided to blow down the engine. I didn't know what was happening until the WOOOSH.
​  The experts can chime in on this but I heard that some crews like to open the blow down cock, shut it off quickly and open it a second time. This should get more ``stuff'' out of the engine.

Grande473 Wrote:
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> ...I heard
> that some crews like to open the blow down cock,
> shut it off quickly and open it a second time.
> This should get more ``stuff'' out of the engine.

Opinions vary on this.  I've never run an engine with power operated blowdowns, which I believe, open and close quickly.  But, it seems to me that opening/closing the valve(s) quickly creates an undesirable shock to the boiler.  I believe to never open more than one valve at a time (one is mandated to be installed on each engine, but may be more - most engines have two, but 3, 4, or 5 may be installed) s-l-o-w-l-y.  Like, take 5 seconds to open it.  Let it blow for 12-15 seconds, and close it s-l-o-w-l-y.  Repeat, if necessary.  You can tell the quality of the water in your boiler by the color, or clearness, of the water in your waterglass. If you've got really shi**y water in your glass it may take several hours to get your boiler cleaned up - if you can, at all.

Where we run on the NSSR we take the water from Lake Superior - literally the cleanest natural water on the planet.  We can blow down once or, rarely, twice a day and still have zero water problems.

OTOH, I've run excursions in parts of northern Wisconsin (south of the Superior watershed) where the water in the glass looked like milk due to contaminants, even with frequent blowdowns.  Here, you just have to blow down whenever you have an opportunity - crossing bridges is really a good place, because bridges are almost always at the bottom of a sag, so your boiler has had a chance to "settle" before the next upgrade. 

Pay attention to what your fireman is doing.  Do not, or at least try not to, blow down if the glass is low on water, or if you see he's dealing with another issue, such as a clinker or hole in his fire.

-John Stein, aka Larry Doyle.

Back in Aug. 2011, I finally rode a Colorado (and New Mexico) narrow gauge steam powered train on the Cumbres and Toltec.  As a bonus to this iconic experience, we had a "steambow" when the fireman blew down the boiler at just the right spot on the way back to Chama.

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