Steam & Excursion > A basic concept about steam operated air compressors.

Remember when you were a kid and used a hand operated bicycle pump?
The hard part of the  'push' always was the last inch --- when you were
pumping up the tire.

Its the same with steam operated air compressors  --- in reality, all types
of air-piston compressors.   You don't actually compress the air towards the tank
until you're trying to force air against a pressure-closed check valve ( at the storage tank).

On train braking systems, using steam operated compressors, it's vital that
when descending grades that the boiler pressure be right at the pop-off
point ( the safeties).   When the boiler steam droops, the air compressors lose their 'snap' ---
at the end of the stroke. 

That seriously decreases the speed at which the main reservoirs get back
to full pressure.  It's a subtle effect, but can be a serious matter..... the engineer 
expects very quick restoration of BP pressure and wants the cars' air tanks refilled 
quickly --- after a brake application...even a 'light-one' of a 10-psi reduction.

During recharge of the trainline, air is flowing from the MR....if that pressure
( and volume of air ) droops, less air actually goes into the train.... and that's a bad effect.

That's why its crucial, on long, descending down grades that the boiler pressure 
be at its strongest --- so the compressors keep their snappy operation 
all the way to the end of the stroke, and especially at the last inch of the stroke!

Its harder to fire a steamer going down hill. ---- because you don't have the dtaft,
and you've got to keep the pressure up ....but, you don't want the safeties blowing,
either.   With oil burners, that's when you'll see them smoking the easiest...
adding more fuel than there is available oxygen supplied to burn it!

​W.
 



Edited 2 time(s). Last edit at 11/29/21 07:17 by wcamp1472.

Mr. Camp has given us another example of how Physics play out in railroading.
Thermodynamics, management of kinetic and potential energy, horsepower, and acceleration in all three axes that we first read about in high school science class are all a part of the operation of railroads.  
Thanks for the insight.

It appears to me that before about 1895, most of the design
'engineering' was done by trial-and-error problem solving.

It took a while for the colleges and universities to develop engineering
curricula.   There weren't a lot of texts, charts and references that were applicable 
prior to then.

By the time trained engineering students percolated up through corporate
layers and company hierarchies ---- about 1915---- that those graduates were
in position to have impact on design and production decisions.

In manufacturing, it's not just providing useful products, you have to solve
the production problems and assembly sequences, jigs and many specialty tools.

The development of reliable stokers is an example ---- about 1910 folks knew about and yearned for
a reliable stokers system for locos.   It took many trials before the first reliable stoker --- the Standard 
Stoker's " Duplex Stoker" --- came about after 1920.    Better variants developed quickly.

But it takes time to develop the people and the skills to generate successful Loco production
compamies.... Lima Loco comes to mind.  And how they 'pushed the envelope' of loco
engineering  and improvements.  Many of their innovations, in actual  service, didn't pan-out
so good...but, that involved things that they had no way of anticipating....

So, I'm continually amazed and a devoted student of ferroequinology .... 
I'm continuously learning new stuff.... and each locomotive restoration is a monument 
to folks' learning and education about steamers..   I'm enthused by the numbers of
new folks entering and succeeding at steam loco preservation and operation.

The other industry category that was exploding at that time 1890s to 1930s, was the
building of Battle Ships for the Navy... it was made possible by the design and manufacture 
of factory facilities and equipment that was larger than the parts they were designed
to produce..... like the gun barrels for the ships' turrets.

Many of the same machine tools were used by corporations and factories for both RRs 
and ships..  Bigger ships meant bigger machines needed to build them...

​W

(not proofed, yet..)



Edited 2 time(s). Last edit at 11/29/21 09:34 by wcamp1472.

And you get to the issue of volume of air being pumped. The good old uniform gas law V1P1T1=V2P2T2 gets you
to that thing in the middle, the equal sign ie a stall. So to get to Wes' peppy performance you need a lot of ratio in
the compressor. Say you've got 250 psi steam and you're looking for 100 psi air, that's 2 1/2:1 so you need 2 1/2
times the area on one side of the compressor to 1 time on the other, wrong! The real number if more like 3 times
that or 7 1/2 to 8:1 to get fast response. So if you've got a 2 1/2"  diameter pressure side ram or piston you'll
need a 7" diameter steam side cylinder. So it's easy to see why locomotives had 2 pumps, why the cross
compound design came into play to build that ratio in two steps. More math, more physics.

Out 

wcamp1472 Wrote:
-------------------------------------------------------

> Many of the same machine tools were used by
> corporations and factories for both RRs 
> and ships..  Bigger ships meant bigger machines
> needed to build them...

Which reminds me of my time in the navy, in the shipyards at Portsmouth VA, I used to cut through the machine shop while traveling to and from our barracks while living off the ship, and observe the equipment and goings on, and was always enamored by the large roller there with the capacity stated in cast letters on the frame,  40'  (yes, 40 feet!) by 1 1/2" plate.  Guess who built the machine, Baldwin Locomotive Works.

Andy

Camp:

My grandfather was a stationary steam engineer for his entire career both in the woods with steam donkeys and eventually handlng the steam power for the Pickering Lbr. Company mill in Standard (Fassler). After his retirement he and my grandfmother would take my sister and I out to the Sierra's Sonora yard. I was "train crazy", my sister was uninterested, but my grandfather would go talk to the crews of the two trains. There would typically be a meet between the upper division and lower division trains.

He would let me wander around with him. It was interesting to hear these guys talk in terms like "she's really steaming good" or comments related to fuel or water consumption. Or talk of a locomotive being "slippery" on a given day.

There was a mystery to steam engines as they seemed to have variabilities that were not necessarliy easy to "file" into some digital formula. It always sounded like the engine crews were talking to him about things that went from general to very detailed stuff that was over my head then and now.

It seems easy to see why engine crews liked one loco or another and didn't care for another one which might just be described as "she just won't steam worth a @$%#!"

With steam power there seemed to be a mystery and "connection" between the crews and their loco that is not present with diesels.

Anyway, thanks for the fascinating insights!

John Mills

 

Re:: sixbit, above.

Very True!

It was common for several members of the same Loco class to 
be labeled as 'dogs'...

Their steaming characteristics bordered on terrible.
There was no particular single factor and no way to prevent
'odd-balls' from occurring.

 It was also puzzling that even after very extensive rebuild episodes  (in -kind),  
that the 'dogs' came out as the same poor-performers, like before their 'heavy-repairs"..

But, there were also ( just as few) Superior Performers in a similar 'class'....
....A few were always "just rarin' to GO!"... You had a hard time holding them back!!

Its hard to tell with large, capable steamers used in today's excursion service.
Largely because the the loads they pull are puny, compared to the sized
trains they were designed and proportioned-for....as far as drafting, valve gear 'setting',
coal quality, and track profiles.

Like the track profiles for the NKP locos, in regular service, was primarily flat-ground..
.. and they use 25" bore pistons on the 700s ---- partly to save on water consumption.  
You'll find other RR's  2-8-4 locos with bores more like 27" .... ( seems like small difference
in piston diameter, but do the math and compare the piston areas, in square inches, exposed
to boiler pressure!  ["Pi 'times' R-squared".... from Geometry class ]).

The NKP Berks are poor mountain climbers--- but they make ideal
excursion engines.  Dual-purpose 4-8-4 locos also work-out well in excursion
service.

Some engines were  "favorites";  others forebode of troublesome trips..
depending on the train 'make-up', on any particular day..  And, soon, everybody
from dispatchers, on down, all knew the 'bad' numbers...
 

But, your memory rings-true; 'dogs' were probably very common,across the USofA!

​W.



Edited 1 time(s). Last edit at 11/30/21 09:30 by wcamp1472.