machinery factor

[Erie Limited]

 

 

Reading a Le Massena article I found the term "machinery factor." Is that a real thing or something known only to the author? And if real, is it something that can be computed and expressed as a number for comparison purposes? 

[CSSHEGEWISCH]

I believe that the machinery factor is how well the drive mechanism (pistons, cylinders, driving wheels, etc.) converts the energy in the steam from the boiler to driving force at the rail.

[gregc]

CSSHEGEWISCH

converts the energy in the steam from the boiler to driving force at the rail.

could it be the friction that needs to be overcome becfore any force is applied to the rails which wouldn't included loss of steam pressure between boiler and piston

[Overmod]

We called it 'machine resistance'.  It is the sum of all "mechanical" losses between piston thrust (practically-measured IHP) and DBHP.  "Machinery factor" is probably a way to reduce this to a percentage -- Bob did love his mysterious little percentages and numerical indices.

It can be measured in other ways, for example between integrated piston thrust and wheelrim torque, to determine certain aspects of mechanical design or practice.

Note that the figure is taken at a particular speed and load, as many of the 'resistances' are nonlinear and can be either greater or less depending on the characteristics at the time of measurement..

[timz]

Dunno if it was a term anyone in the industry used. If it was, first guess is it was a percentage -- drawbar horsepower divided by cylinder horsepower. So it would decrease as speed increased.

Maybe some PRR test-plant reports are online at hathitrust.org or someplace -- they might mention "machinery factor".

[sgriggs]

I don't think I've ever seen that term in a PRR test report.

[Erie Limited]

Thanks for the replies. They are as I expected, more a Le Massenaism than a widely recognized term. 

[feltonhill]

LeMassena's machinery factor is calculated using cylinder volume and driver diameter:

2x((bore^2 x stroke)/driver dia.)

I took his table in June 1968 Trains, "The Big Engines," and converted it into a spreadsheet sometime in the late 1990s.  I made a note that his machinery factor was the same as Baldwin's engine constant.  The source for this is Johnson's book, The Steam Locomotive.  The engine constant is a part of the Kiesel formula, which is used to calculate tractive force at speed.

As a caution, LeMassena sometimes uses drawbar pull and tractive force interchangeably.  They aren't.  TF is calculated at the cylinders; drawbar pull is measured at the rear of the tender.

[gmpullman]

From an Alco data booklet:

Alco_data_hilite by Edmund, on Flickr

Alco_data_0001 by Edmund, on Flickr

Alco_data_0002 by Edmund, on Flickr

Alco_data_0003 by Edmund, on Flickr

Alco_data_0004 by Edmund, on Flickr

Alco_data_0005 by Edmund, on Flickr

I hope this is helpful —

     Regards, Ed

[Erie Limited]

Thank you Ed! That is most helpful. So it turns out that machinery factor is 25 pounds per ton on the drive wheels. A typical 4-8-4 with 280000 lbs on the drivers would have a machinery factor of 3500 lbs. (140 tons x 25 = 3500 lbs) But that was before Timken and its Four Aces. An all roller bearing locomotive might rate somewhere near 5 lbs/ton, maybe 6 if those three office girls in Chicago were of the hefty type.

[timz]

Erie Limited

An all roller bearing locomotive might rate somewhere near 5 lbs/ton

The 25 lb/ton it mentions isn't just driver bearing resistance -- it's all losses between the steam in the cylinder and the wheelrim. Roller bearings won't decrease that loss by anywhere near 80%.

[gmpullman]

Erie Limited

Thank you Ed! That is most helpful.

You might like to browse a Timken study that I scanned a while back regarding roller bearing side rods and the quest to reduce weight and friction of the reciprocating parts of a steam locomotive.

Timken_Rods_Fig. 16 by Edmund, on Flickr

The album with the rest of the pages can be found here:

https://www.flickr.com/photos/gmpullman/albums/72157673726478087

Regards, Ed