Steam & Excursion > Steam locomotive tender question

When the water from a tender on a steam locomotive is pumped from the tender into the boiler, how is thermal shock avoided? I know the water coming from the tender is no where near the temp of that already in the boiler and I've often wondered about how it's overcome especially in Winter.

apollo17 Wrote:
-------------------------------------------------------
> When the water from a tender on a steam locomotive
> is pumped from the tender into the boiler, how is
> thermal shock avoided? I know the water coming
> from the tender is no where near the temp of that
> already in the boiler and I've often wondered
> about how it's overcome especially in Winter.

1) When the steam injector is used, the water is preheated by the steam in the injector.

2) When a feedwater system is used, the water from the tended is first preheated by exhaust steam, then pumped into the boiler.

With a water injector, steam is focused through a nozzle to impart velocity into the water coming up in front of it.  As the steam mixes with the cold tender water on its way down the delivery pipe the water is heated some, but no where near the 380~ish degrees the boiler water is at.  There is some thermal shock going on, but that is why the water is injected up at the front of the boiler by the smokebox where the shock is least harmful.

Every time you inject water into the boiler it cools the boiler water slightly which can hinder a fireman on a poor firing locomotive or it can help a fireman on a great firing locomotive.

On 3985 we used an injector system and it mixed steam from the boiler to the water as it was injected into the boiler to override the pressure against the boiler check valve and prewarm the water as it goes in. On 844 we had a Worthihngton feed water pump that pumped the water up to a feed  water heater on top of the smoke box preheating it before it entered the boiler.

Bob Krieger
Cheyenne, WY

Lurch Wrote:
-------------------------------------------------------
> ...  There is
> some thermal shock going on, but that is why the
> water is injected up at the front of the boiler by
> the smokebox where the shock is least harmful.

Thanks, I learned something.

Lurch Wrote:
-------------------------------------------------------

> Every time you inject water into the boiler it
> cools the boiler water slightly which can hinder a
> fireman on a poor firing locomotive or it can help
> a fireman on a great firing locomotive.

This can be a good thing.  If the fireman and engineer work well together,
they will try and coordinate the use of the injector when steam is not in
higher demand.  The idea is to inject water just prior to the valves popping,
thus not wasting steam off the top.

I've learned alot myself. Thanks for all the answers to a long standing question I've had about the way this works.

A firemans' technique can make a big difference to a boiler.  There are two techniques which have minimal thermal effect on a boiler.  Best is to run the injector or feedwater continuously at a rate equal to putting water into the boiler at the same rate as the engine uses steam.  This maintains a uniform temperature.  The other technique, used more often with injectors than with FW heaters, or when demand will vary as in switching, is to run the water supply full force in short bursts of about 10-15 seconds, watching the water glass and steam pressure gauges to determine when to repeat the cycle.  This does not put enough cold water into the boiler to cause shock.

Under no circumstances should a fireman run the water supply full force 'till pressure starts to drop or the boiler is full, then shut it off 'till pressure rises or water visibly drops in the glass.  This creates variations in the boilers temperature, which is harmful.  The fireman must plan ahead and anticipate, rather than respond to, demand.  It's a common mistake made by newbies, though some old hats never do quite get the hang of it.

The boiler will tell you by making cracking, popping, or clicking noises that you are mistreating it.

This raises the question of why different roads used different combinations of providing water to the boiler.  Before feedwater heaters, it wouldn't be uncommon to have two injectors.  Once the various feedwater heater systems came to be, there were many roads who used the one injector, one feedwater heater combo.  I was surprised when I visited the 261 group that 261 has two injectors, no feedwater heater.  Then the various feedwater heaters, Elesco, more than one kind, Coffin, Worthington........

When running locomotives with injectors only (majority of locomotives running today) pressure fluctuations are a constant.  A good fireman on an oil burning boiler has two options.  

First pinch the water valve down to a minimum to trickle water in to the boiler (difficult on many types of injectos, but not impossible).  

The second and most common technique is to pick a 3-5psi range to run withing, say 170-175psi.  When the pressure climbs to 175 turn the injector on and allow the pressure to slowly fall until about 170 then kill the gun (turn off the injector).  Allow the pressure to climb back up to 175 and repeat.  Logging and shortline locomotives have been run this way for many decades.

nycman Wrote:
-------------------------------------------------------
> This raises the question of why different roads
> used different combinations of providing water to
> the boiler.  Before feedwater heaters, it
> wouldn't be uncommon to have two injectors.  Once
> the various feedwater heater systems came to be,
> there were many roads who used the one injector,
> one feedwater heater combo.

Two feedwater systems are required to be servicable at the start of the day, at least one of which must be an injector.

If one fails en route the engine may continue in service. If both fail the engine must be taken out of service immediately.

Axle pumps (crosshead pumps) were also commonly used in 19th century.

apollo17 Wrote:
-------------------------------------------------------
> When the water from a tender on a steam locomotive
> is pumped from the tender into the boiler, how is
> thermal shock avoided? I know the water coming
> from the tender is no where near the temp of that
> already in the boiler and I've often wondered
> about how it's overcome especially in Winter.

Tender water will normally be about 39 to 60 degrees F.

An injector will raise it to 160 to 180, a feedwater heater 180 to 200.

Injectors do not perform well, sometimes not at all, with warm tender water.

nycman Wrote:
-------------------------------------------------------
> This raises the question of why different roads
> used different combinations of providing water to
> the boiler.  Before feedwater heaters, it
> wouldn't be uncommon to have two injectors.  Once
> the various feedwater heater systems came to be,
> there were many roads who used the one injector,
> one feedwater heater combo.  I was surprised when
> I visited the 261 group that 261 has two
> injectors, no feedwater heater.  Then the various
> feedwater heaters, Elesco, more than one kind,
> Coffin, Worthington........

Many reasons:  Cost, complexity, not invented here,
fear of change, etc.

Now 'd l' knows a bit more about those three pieces of machinery too. Now if he can just figure out where the ignition keys went.

I have also seen pictures and diagrams of a series of pipes and trays that were designed to disperse the water as it dropped in from the top of the boiler.  This was thought to be less stressful than a solid stream of water.

This may have been a mostly British practice?

Kimball Wrote:
-------------------------------------------------------
> I have also seen pictures and diagrams of a series
> of pipes and trays thainto were designed to disperse
> the water as it dropped in from the top of the
> boiler.  This was thought to be less stressful
> than a solid stream of water.
>
> This may have been a mostly British practice?

Never heard of that.

D&NE 28 on left side just dumps the water into the boiler, above the waterline. The right side has an interior pipe fitted to sorta spray the water into the steam space, at the same height above the waterline. Both are Ohio injectors.

Go figure.

John

I'll have to find that book and scan it up to TO.

Pennsy guys know this...

On "standard" design Pennsy engines (K4, L1, Later H9/H10, E6, G5, etc..) fitted with two injectors and typically feeding the water thru  the boiler checks (mounted on the upper blackhead),  the feed water was piped directly over the crown sheet and forward,  way up near the the interior of the front flue sheet.

Pennsy folks used the hot water above the crownsheet to re-heat the injectors' water before turning into the boiler.
Typically, on  those engines fitted with lifting injectors , the two injector feed pipes faced each other, leading to a casting with two discrete boiler checks.  (One Sellers, one Nathan. --- per Fred Westing).
 
Those locos fitted with non-lifting injectors, used two separate checks mounted on the blackhead's rear, upper corners, heating the feedwater  in two separate feed pipes, right over the crown sheet.
.
With lifting injectors, firemen could verify good operation by feeling the injector's bare water-supply pipes --- if the pipe was nice and cold, she was feeding water correctly; if the water pipe was Hot, something was not going well, and water was NOT being fed to the boiler.  Lifting injectors are much better at really fine water flow adjustments, and the water valve can be squeezed to nearly OFF, before the siphon action is lost.

With the non-lifting injectors, the water in the blackhead-mounted supply pipe is under pressure from the injector, and is hot, but not as HOT as boiler steam.   Low rates of Water Flow regulation is not nearly as precise as with lifting injectors.

Never heard any reports of 'Bowling alley noises' or similar pops and bangs, reported on PRR engines, so equipped.

Wes C.
 



Edited 2 time(s). Last edit at 04/28/15 16:14 by wcamp1472.

Top mounted boiler checks did spray the water onto a plate to disperse it better.

Most omdern designs used top mounted checks, and a lot of rebuilt/upgraded
engines got them, too.