I have read and heard much discussion regarding how “hooking up” the reverse lever affects the operation of a steam engine. This summer, several friends and I decided to see what we could learn about this practice through the use of a steam engine indicator, a steam traction engine, and a Prony brake. I know that this site is for railroad discussions, but thought that our experience might be relevant to a few of the steam guys here. Would gladly repeat the exercise if someone would volunteer a locomotive.

The attached indicator card was taken in July, 2014, from a 23-90 Baker uni-flow steam traction engine at the Miami Valley Steam Thresher’s Show at Plain City, Ohio. The card was taken with a Robertson-Thompson indicator which was equipped with a Victor reducing motion and a #60 spring. (Sixty pounds of pressure moves the pencil upward one inch.) A three-way valve was used to connect the indicator, alternately, to the two ends of the cylinder. After taking a few conventional cards, we proceeded to take a look at how “hooking up” affects the shape of the indicator card.

Our first move was to hook up the reverse lever and then increase the load on the Prony brake as far as we could without reducing the speed of the engine. We then took a card from each end of the cylinder. Once these cards were taken, the reverse lever was pulled, “down in the corner” and the shorter diagrams were recorded. Because the engine was running on the governor there was no change in speed. The load on the Prony brake remained constant: therefore the horsepower was constant.

The MEP was determined by measuring the area of the diagram with a planimeter, and dividing that by 3-inches, the length of the diagram.

Red diagram:
.99 sq. inches/3-inches = .33-inches, the height of diagram in inches.
.33-inches X 60 lbs/inch, the rating of the spring in the indicator, = 19.8 PSI, the MEP.

Blue diagram:
1.04 sq. inches/3-inches=.35-inches
MEP =.35 inches X 60 lbs/in = 20.7 PSI

Because there was no change in RPM, and no change in the load on the brake, the horsepower was constant for both the red card and the blue card. Theoretically, there should have been no difference in the average pressure, or MEP. The difference in the horizontal lengths of the cards was due to the string to the indicator not lying flat on the pulley.

What these cards show is that with the late cut-off, (red card) the governor has to close down significantly to limit the horsepower and speed to that which was obtained with the earlier cut-off. In other words, when the reverse lever was hooked up, the piston valve helped to restrict the flow of steam to the cylinder. When the lever was down in the corner, the governor was the primary controlling factor. On a locomotive the throttle would have to be closed to achieve the same result.

The points of release are identical for both cards. However, the start of compression is later when not hooked up. I believe that is the result of Baker’s unique design of the piston valve. On many uniflow engines, the points of compression and release are fixed.

We did not pay much attention to horsepower, other than to keep it constant for both sets of cards.

It is my hope that we will be able to repeat this exercise next year, but with the benefit of what we can learn from this first attempt. Maybe someday we will get a chance to try it on a locomotive.

Bruce E. Babcock

I've always wanted to see a comparison of identical engines but with one being worn out and no longer square under the same demands. When I've run an engine under heavy loads on fluctuating grades, I've always hooked it up as high as I could to control speed before adjusting the throttle, and vice versa. However, on engines that lope well below being centered, it's much harder to run the engine efficiently.

Hi Bruce:
The Valley Railroad would be pleased to have "cards run" on our locomotives.
Both are fairly typical, inside admission, piston valve 2-8-2s, one saturated (plain piston valve), one superheated (with "Trofimoff" piston valves).
Both have recently recieved new piston and valve rings.
With proper scheduling, it would be possible to do both locomotives on successive days when one is coming out of service for its 31 Service Day Inspection.
Lets, chat...
J.David

The Governor on a traction engine is like your early "auto" control long before electronics came about. But it is only controlling steam input from throttling.
Cutoff allows the steam to expand to do its power with expansion and not use excessive steam. Late cutoff means full steam pressure power is applied on the piston till cutoff gets made and when exhausted there may still be plenty of steam power that gets unused blowing out the stack. Its finding a balance as raw power is largest when the piston is midway. (Thats power transferred to the wheels), its the idea of lifting a weight on a stick depending where the weight is located on the stick. Late cutoff means you are still introducing steam into the chamber. But it does not mean the best steaming efficiency. How much pressure that steam is also says how much power you get out of it,
so playing with the cutoffs vs steam pressure is your art form to find your best operatable steaming.

.

Since this is on a traction engine and is undoubtedly saturated, I would be curious about the steam quality for the two scenarios, and how that may play into efficiency losses when operating at full gear cutoff.

Is steam quality, like steam temperature, assumed to be equal in both cases?

R.C. Whitehead

Mr. Whitehead and Mr. Anderson,

Great questions!

I now suspect that I know how Wylie Coyote felt when he realized that he had run beyond the edge of the cliff.

If steam consumption was measured at the point of release, pressure, volume, and density would be equal for both scenarios. Then to get steam consumption, it is necessary to subtract the steam that is compressed, in both scenarios. Without doing the math, it appears that the amount of steam compressed when hooked up would result in a lower calculated steam consumption.

I believe that it is important to remember that this is a uniflow engine, and that the temperature of the cylinder is greater than that of a counter-flow engine, especially at the outer ends. This should result in lower condensation in the cylinder. Calculated steam consumption is always lower than actual consumption because of condensation.

Also, I neglected to record an atmospheric line, so it is not possible to locate the line of total vacuum. And I do not know the clearance volume for a 23-90 Baker uniflow. Both of these are needed to calculate steam consumption.

This is saturated steam, no superheat.

I will gladly accept any help in interpreting these cards.

Bruce E. Babcock

There's another factor which is the scientific reality of physicalness of what steam is, and why a fireless cooker works.

A fireless cooker is injected with high pressure high heat water, just that alone generates steam, as steam is used, the pressure drops, the water boils further producing more steam.

Having said that, one must consider water point to steam temperature factor?
The superheaters are about "drying" the steam of water and vapors for pure steam and this gives the steam a bigger "pop" for the pressure. The steam hitting the cylinders should be even hotter than when it was perculating in the boiler and perhaps in a higher pressure situation. When that steam enters the cylinder, it expands and the temperature reactions on the steam may give it that pop like we see in the fireless cooker.

Kelly,

Steam consumption is calculated by determining the pounds of steam in the cylinder, including the clearance space, at any point between cut-off and release, and then subtracting the pounds of steam that are compressed in the clearance space at the end of the stroke.

On the cards that I posted earlier, the pounds of steam in the cylinder at the point of release is constant, whether or not the reverse lever is hooked-up. This is because the release occurs at the same point in the stroke, and at the same pressure, in both cases. The pounds of steam in the clearance space, however, is different because of the difference in the pressure. In this case the difference is considerable, 120 PSI, vs. 33 PSI.

Steam consumption is generally reported in pounds of steam per hour per indicated horsepower. Using the MEP of 20 PSI, and making a few assumptions, I determined that the cards represent 19.8 indicated horsepower, or IHP. The engine is rated at 90 brake horsepower, or BHP.

I will spare you the tedious calculations.

According to my figures:

Hooked up, the engine was consuming 39.3 pounds of steam per hour, per indicated horsepower.

When down in the corner, the figure is 44.2 pounds of steam per hour, per indicated horsepower.

These cards are from a uniflow engine. This is the reason that the point of release did not change. Also, Baker piston valves on uniflow engines, had a third spool near the center of the valve that controlled the point where compression began. Note that compression does not begin at the same point on both the red and blue cards that I posted earlier.

When running down in the corner, this engine sees 33 PSI on every stroke. When running hooked-up, it sees 120 PSI on every stroke. On a 10 inch piston, this means the difference between 2,590 and 9,420 pounds of force on the wrist pin, crank pin, etc.

Bruce E. Babcock

So when I've been told that leaving an engine in the corner "beats them to death" it could actually be the opposite? I've wondered about the long push of steam when your down in the corner versus the smack of full boiler pressure.

Our regular engineer on our Climax claims the further down in the corner he runs the less bolts he finds to tighten....of course it's a Climax so there are always plenty of bolts to tighten....

Ben True

DGVR