Steam Traction Engine Horse Power Ratings

Case engine

Case engine on the incline at the Winnipeg Fairgrounds in 1910.

Content Tools

131 Robin Road, Blackwell, OK 74631

There seems to be a lot of confusion on horse power ratings. I am not going into how you figure brake horsepower because I think most everyone understands this. If a steam traction engine is tested on a prony brake and the brake is correctly built and operated, it will give you a correct answer.

The big problem seems to be in the old 'Nominal ' horse power ratings. Some seem to think the nominal rating as used on steam traction engines was a boiler horse power rating, while others have said it's a draw bar rating. Both are wrong.

Just what is 'Nominal' horse power? In Steam Engine Catechism by Robert Grimshaw, M. E. and I quote:

Nominal horse power does not mean anything in particular. It corresponds to 'as long as a piece of string,' or 'as big as a lump of chalk.'

Mr. Webster says 'Nominal'-- named as a mere matter of form, being trifling in comparison with the actual value.

The old nominal rating was very popular and some companies used it to the very last.

The question is, just how did they determine a certain horse power rating for a given engine? I will quote what one builder of steam engines said on this subject:

'Steam farm and traction have been rated very much below their actual or brake horsepower, which is to be regretted. This practice of underrating has existed since steam engines for driving threshing machines were first built, and has grown up with the business. If we look into history and causes, we find that the early method of driving threshing machines was by horses, and when engines were first used for threshing, a ten horse-power engine was supposed to supply about the same amount of power as a lever power driven by ten horses. From the time of those early engines to the present (about 1910) the competition of different manufacturers all endeavoring to furnish the most powerful engine of a given rating, and the raising of the steam pressure from 60 to 150 or 175 pounds (which was done without reducing the size of the cylinder of a given rating), has caused the rating of engines of this class to become more and more confusing. The relation which the rated nominal horsepower bears to the actual size of the engine varies so greatly that, in reality, the 'rated horse-power' gives only a very indefinite idea of the actual size of an engine. There are reasons why it is preferable to indicate the size of an engine by size of its cylinder, instead of by its rated horsepower; for example, to say a 'nine by ten' rather than a 'fifteen horse' engine. However, besides the cylinder size, the steam pressure carried and the speed are also important factors in determining the amount of horsepower an engine will develop, and therefore a brake rating based on the actual load the engine is capable of carring is the only satisfactory method.'

People seem to take it upon their own to rate engines, which adds to the confusion. For example, I've seen the 65 HP Case listed as 22-65 HP and 80HP Case as 28-80. In 1910 the Case Company gave all their engines a brake horsepower rating and from that time on Case engines were never given a nominal rating. So, a rating like 22-65 is not correct and was never used by the Case Company. This used to really blow E. C. 'Big Mac' McMillan's dress up for someone to call an 80 Case a 28-80 or a 65, a 22-65.

Before 1910 the old 9 x 10 Case was a 15 HP, from 1910 on it was a 45 HP and not a 15-45 HP.

Some companies did go ahead and give both a nominal and a brake horsepower rating, example 25-75 Russell and 16-60, 20-75 and 25-90 Nichols and Shepard.

Most of us who have been around engines for a number of years pretty well understand the size of an engine. For example, the 23-90 Baker I do not consider larger than 20-75 Nichols and Shepard. The Baker will just about develop its 90 HP on a brake test but 20-75 Nichols and Shepard will go over its 75 HP rating. Another rating that could confuse the customer in the old days was the 19-65 Port Huron Longfellow as compared to a 65 HP Case. In the Port Huron catalogue it says that their engine rated at 19-65 will develop 65 HP and that another company with a 10 x 11 cylinder and 229 sq. ft. heating surface will also only develop 65 HP. Now I am very high on the Port Huron Longfellow's and think that they are a wonderful engine, but there is no way one can compare in horse power with a 65 HP Case. I do not think there has ever been a better or more knowledgeable steam engineer than LeRoy Blaker. LeRoy could not do what he wanted to with his 24-75 Port Huron Longfellow on the brake. He even simpled the low pressure cylinder and still could not develop the power needed to win the brake contest. So he got a 65 HP Case and pretty well won the maximum brake test with his 65. So when the companies went to a brake HP rating it was still somewhat confusing as to what size engine you were getting by the HP rating given by the company.

Emery Pettit's Avery 30 HP 'Alberta & Saskatchewan Special', south of Tonkawa, Oklahoma. This engine now belongs to Midwest Old threshers, Mt. Pleasant, Iowa.

In the past, I have stated that the 40 HP Undermounted Avery was very overrated as compared to the large engines. I will try and tell you why I think this is a true statement and you can be the judge. I have also said, that the '30 HP' Alberta and Saskatchewan special and 40 HP Undermounted engines were for all practical purposes the same engine. I will refer to the specifications of the Avery Undermounted engines taken from a 1914 Avery Catalogue. You will see that the only difference given in these engines themselves is the thickness of the dome sheet, 7/16 on 30 special and 3/8 on 40 HP. All other specifications are the same for both engines except the pop set at 200 pounds on 40 HP and 175 HP on 30 special. Now what this amounts to for all practical purposes is that the pop or safety valve is turned down about one and one fourth turns more on their 40 HP engines.

After doing a little homework I will try and show you why the 40 HP Undermount is overrated.

The 40 HP Undermounted has two 7 x 10 cylinders with 769.69 cubic inch displacement.

The 36 HP Rumely has two cylinders 73/4 x 14 with 1320.85 cubic inch displacement. The 36 HP Rumely has 71% more C. I. D. than 40 Avery.

The 110 HP Case has one 12 x 12 cylinder with 1375 C. I. D. or 76% more than 40 Avery.

Even a 65 HP Case with one 10 x 11 cylinder has 863.94 C. I. D. or 12% more displacement than a 40 HP Avery.

Now speed and pressure are both factors but the 36 HP Rumely and 110 HP Case are not hot water engines.

I did not figure the 35 HP Nichols and Shepard--it has two 77/8 x 11 cylinders and my old friend Harve Guston when his 35 HP Nichols and Shepard was unloaded at Kildare, Oklahoma in 1915 the pop was set at 210 pounds. This was a great old engine--Harve always called it 'Old Joe.'

Some of you older fellows in Ohio may remember LeRoy Blaker and Louis David battling each other on the prony brake, tug of war and belting both engines together. I was not there, but understand the 65 Case owned and run by LeRoy Blaker held its own with Louis David's 40 HP Undermount. That is the reason I think that the 40 HP Undermount was overrated.

One of my favorite engines is the Advance Rumely Universal. I think that the Advance Rumely Company came out with this engine about 1915. Some say they copied the 65 HP Case. In some ways I think they improved the design. This engine had a good, well made butt strap boiler with wing sheet construction. It had that famous Advance exhaust. I somewhat question the Advance Rumely Company's using the old Marsh valve gear when they came out with this engine. Some of the old timers said that all the Marsh valve gear would do was reverse the engine. This is somewhat true. The valve gear also has an influence on the horsepower an engine develops. One thing the Marsh gear did was cut off at 6/10 of stroke. Maybe they could not develop the power of an engine with a radical gear. But the old Marsh gear had its good points. Mr. Dean Schellhous from Fairfield, Iowa has pulled the sawmill at the Mt. Pleasant, Iowa show for years with his nice Advance Rumely Universal. This is a commercial sawmill with a professional crew. They really saw. This engine does a wonderful job. I do not know what horsepower this engine develops but it sure gets the job done. There were sixty-six large engines at Mt. Pleasant last year. I have noticed for years that no one takes the job away from Dean and his Advance Rumely. When you get a combination of a good engine and good engineer it is a hard combination to beat.

SPECIFICATIONS OF AVERY DOUBLE UNDERMOUNTED STEAM TRACTION ENGINES

Rated Horse Power

18

20

20

22

30

30

40

   

Special

  

Special

 

CYLINDERS

       

Bore

6

6

6

7

7

7

7

Stroke

10

10

10

10

10

10

10

FIRE BOX

Width

271/2

271/2

271/2

31

31

31

31

Length

38

54

54

431/4

60

60

60

Height above Grates

281/2

365/8

343/4

29

42

411/4

411/4

Thickness of Crown Sheet

5/16

5/16

3/8

5/16

5/16

3/8

3/8

Thickness of Flue Sheet

1/2

1/2

1/2

1/2

1/2

1/2

1/2

Square feet Grate Surface

71/4

10.3

10.3

9.3

12.9

12.9

12.9

FLUES

Size

2

21/2

2

2

21/2

21/2

21/2

Length

84

78

78

84

84

84

84

Number

50

41

50

54

50

58

58

SHELL AND PLATES

Inside Diameter of Shell

32

32

32

36

36

36

36

Thickness of Shell

5/16

5/16

3/8

5/16

5/16

3/8

3/8

Thickness of Throat Sheet

3/8

3/8

7/16

3/8

3/8

7/16

7/16

Thickness of Flue Sheet-Front

1/2

1/2

1/2

1/2

1/2

1/2

1/2

Thickness of Fire Box Sheet Outside

5/16

5/16

3/8

5/16

5/16

3/8

3/8

Thickness of Dome Sheet

3/8

3/8

7/16

3/8

3/8

7/16

3/8

Thickness of Rear Head

3/8

3/8

7/16

3/8

3/8

3/8

3/8

Number of Handhole Plate

7

8

12

7

8

14

14

Number of Washout Plugs

2

1

2

2

1

2

2

Size of Steam Pipe

2

2

2

21/2

21/2

21/2

21/2

Total square feet Heating Surface

2163/4

222

2181/4

2391/4

294

330

330

Working Pressure per square inch

150

150

175

150

150

175

200

Revolutions per Minute

250

250

250

250

250

250

250

FLY WHEEL

Diameter

401/4

401/4

401/4

401/4

401/2

401/4

401/4

Face

101/4

101/4

101/4

101/4

101/4

101/4

101/4

CRANK SHAFT

Diameter

31/2

31/2

31/2

31/2

31/2

31/2

31/2

Number of Bearings

4

4

4

4

4

4

4

Total Length of Bearings

211/2

211/2

211/2

23

23

23

23

SHAFTING

Diameter of Intermediate

3

3

31/2

31/2

31/2

31/2

31/2

Diameter of Countershaft

31/2

31/2

4

4

5

5

5

Diameter of Rear Axle

5

5

51/2

51/2

6

6

6

Diameter of Front Axle

31/2

31/2

31/2

31/2

31/2

31/2

31/2

GEARING

Face of Spur Gears

3

3

5

5

5

5

5

Face of Bull Gears

4

4

6

6

6

6

6

Number of Bevel Pinions in Comp. Gear

3

3

3

3

6

6

6

Number of Traction Speeds

2

2

2

2

2

2

2

Miles per hour on Fast Gear-250 RPM

2.3

2.3

2.38

2.38

2.63

2.63

2.63

Miles per hour on Slow Gear-250 RPM

1.83

1.83

1.57

1.57

1.9

1.9

1.9

DRIVERS

Diameter

65

65

67

67

80

80

80

Face

20

20

26

26

26

26

26

Thickness of Tire

5/8

5/8

5/8

5/8

5/8

5/8

5/8

FRONT WHEELS

Diameter

46

46

46

46

52

52

52

Face

10

10

12

12

12

12

12

Capacity of Water Tanks-Gallons

325

325

350

350

450

450

450

Capacity of Coal Bin-Pounds

400

400

400

400

500

500

500