Over on Railroad.net forum, a gentleman posed questions about water brakes.

Sounds like something that could be interesting.

Anyone know about these beasties?
Or, can someone point me to references/resources?

Thanks

Hank Morris

http://www.azohwy.com/y/ymavlyrr.htm
hankmorris@earthlink.net

Extracted from the link below:

"Cylinder Compression Brakes"

"Cylinder compression brakes were much used prior to prehaps 1900. Atmospheric
air as a compression medium was at first often used, but owing to it heating
tendency and the sucking in of cinders and hot gases from the smokebox, it
was soon discarded in favor of steam vapor. The Le Châtelier water brake was
perhaps the best known of these brakes and was applied to many engines
operating on heavy grades. This brake consisted of a globe regulating value
in a pipe line that admitted hot water from the boiler to the exhaust
passages of the cylinders. There it immediately formed a heavy vapor which
was drawn into the cylinders by the the suction of the pistons. The reverse
lever, which had been set in mid-position, was
now gradually moved into back gear until the desired braking power was
obtained.
"The device was simple and effective but was naturally subject to abuse in
operation, and cylinder-head relief valves were fitted whenever it was
applied. Its purpose was the same as that of the independent air brake, which
is to facilitate train speed control and to assist in relieving the train
brake shoes from heat on long grades."

Trains Magazine had a technical article some number of years ago on the use
of the water brake on D&RGW articulateds: assume that it was written by
Robert A. LeMassena, who would be one to know the subject.

Bruce B. Reynolds, Trailing Edge Technologies, Glenside PA and Niles IL


http://www.webcircle.com/users/cobrandt/9906.txt
cedressel@chartermi.net

Re: Compression Brakes

We once had to take a locomotive with a couple of tires that would shift when heated by over-braking, down a 3 mile 3.5% grade, with no train. To avoid tire heating we put the reverser in the opposite direction and regulated the speed by adjusting it. It doesn't take much.

We have steam chest pressure gauges on our engines which in this instance indicated air pressure pumped by the cylinders. Our highest reading was 120 psi.

Our engines burn oil, so on a downgrade there were no combustion products available to be sucked in through the exhaust nozzle. We also believe that the cylinders draw air in initially until the dry pipe (reservoir) air pressure builds up to what is needed for braking, after which the cylinders merely keeping that pressure up without requiring additional intake air, therefore not drawing through the smokebox until additional braking force is required, and then only for a short while.

The locomotive could be stopped on the hill with compression.

We have also experimented using compression as the independent brake when bringing a train down this hill. It works well.

I have been told that the Northern Pacific Mallets that served as helpers on Stampede Pass used compression to return to the starting point. They may have had relief valves, at least on the low pressure cylinders. There were no modifications to these locomotives for compression braking.

Thank you.

steamrr@mashell.com

Jack;

> The locomotive could be stopped on the hill
> with compression.

I presume you are talking about piston valved locomotives? When I have tried this trick with "our" shay, the effect was not that noticable; mainly a bit more noise through the drifting valves.

Any comments/thoughts?

John Stewart
Ottawa, Canada.


Ottawa CMST Shay
freewrl-1@rogers.com

Yes, we have only tried this with piston valve engines. We are rebuilding a slide valve loco now and I'm curious, now, about using it with compression. I have not thought this out, but do you suppose the valves lift from the seats under compression?

Thanks,
Jack


steamrr@mashell.com

but do you suppose the
> valves lift from the seats under
> compression?

Yes they do.

Dave

irondave@bellsouth.net

The Le Châtelier water brake is something that I have always been fascinated with, because of its operational concept, and its mystery. Why was the Rio Grande the only US road to use it, and why was it removed from the surviving Rio Grande 2-8-2’s on the C&TS, the engines most able to employ it of today’s US steam operations?

Installation was simplicity itself. A ½” angle valve was plumbed into the backhead below the waterline of the boiler. This ½” line ran forward to the saddle, where it split into two branches that connected with the exhaust passages in the saddle (not the steam passages). When this valve was opened, boiler water would run into the exhaust passages where it would it would flash into a mixture of very wet steam and water. Depending on how much the engineer opened the valve, he could get a fair amount of this mixture to come out of the stack. If done while the engine was stopped, this would have absolutely no tendency to cause the engine to try to move, since the exhaust passages are always open to the atmosphere.

Boiler water, (388 degrees at 200 PSI) when released into the atmosphere, partially flashes to 212 degree steam by using the energy stored in the water due to its being 176 degrees hotter than the 212 degree boiling point at atmospheric pressure. The water does not have enough energy in it to entirely flash to steam, most remains as liquid water (reduced in temp. to 212), albeit as a very fine mist.

In operation, the engineer would close the throttle, open the valve, open the cylinder cocks, and move the reverse lever a few notches into reverse, regulating the reverse lever for the amount of braking desired, and regulating the valve to supply just enough water to keep a wisp of steam coming out of the stack. The cylinder cocks must be left open at all times to allow the water a place to escape, otherwise severe damage to the engine could result. This makes for a very noisy operation.

The purpose behind adding the boiler water to the exhaust is twofold. First, its volume breaks the vacuum that would form in the exhaust passages so that smokebox gasses donÂ’t go into the cylinders. Even on a perfectly clean oil burner, these gasses would be at least 400 or 500 degrees, combined with the added heat of compression, would make short work of the oil coating in the cylinders. Second, by compressing the mist of liquid water, the heat of compression is absorbed by the water, at most turning it back into steam, which is then blown out of the cylinder cocks, leaving the cylinders considerably cooler.

The Rio Grande #683 (a slide valve engine) at the Colorado Railroad Museum is the only engine I know of that has an intact water brake. The valve is at the 3 o’clock position on the knuckle of the backhead, and the pipe is intact into the saddle. I have seen other Rio Grande engines that are not lagged in that area of the back head that have a plug installed in that same 3 o’clock position, and the K-36’s on the C&TS have the two ½” pipe nipples sticking out of the saddle, indicating to me that they had water brakes installed in the past. Why were they removed?

The Rio Grande K class engines running today are fitted with a “drifting valve” which supplies steam from the turret to the steam chests (not the exhaust passages) and are commonly used for compression braking. Use of these valves for this has never made much sense to me, since they do nothing to prevent smokebox gasses from entering the cylinders, unless it is assumed that the valve and piston rings leak through to exhaust enough that this steam gets past them to break the vacuum in the exhaust passages after all, a poor situation to begin with.


kelly@strasburgrailroad.com

In the era of hydrostatic lubricators, how would you adequately lubricate the cylinders, or even the large surface of the slide valves?

I would think that the Le Chatlier "water" would remove an auxiliary source of oil to the cylinders as well.

johncb@u.washington.edu

> In the era of hydrostatic lubricators, how
> would you adequately lubricate the
> cylinders, or even the large surface of the
> slide valves?

> I would think that the Le Chatlier
> "water" would remove an auxiliary
> source of oil to the cylinders as well.

Good question, and not just for hydrostatic lubricators, but mechanicals as well, since they both deliver nominally the same amount of oil.

All I can guess is that since the engine is running as a compressor, no oil would be working through the engines and out the stack as in normal operation, but instead would be building up in the steam chest, with no outlet, other than out the cylinder cocks.


kelly@strasburgrailroad.com

Hi Kelly:

Your reference to "severe damage" to the engine is probably the main reason the various forms of water brakes have never been very successful or widely used.

The key to understanding the water braking principle is to review an indicator card. The steam engine is a volumetric device and an indicator card is a "pressure volume" diagram that shows what happens to the steam pressure in the cylinder as the piston opens and closes swept volume throughout a full revolution.

All steam engines have some degree of compression when operating with the throttle open going up the hill. This represents negative work and detracts from the positive work of admission and expansion. Therefore, compression is a bad thing going up the hill except for its ability to "cushion" the machinery while going over the dead centers. In most locomotive valve gears compression increases as cutoff is shortened. This is because the exhaust ports open earlier during release (power stroke) and close earlier during closure (exhaust stroke). This is beneficial during high speed operation as the cushioning effect helps prevent the motion work from hammering itself severely when running fast.

However, going down the hill is a different thing. When going down the hill the best policy is to run the valves at full cutoff so they wear more evenly on the full stroke in the valve cages and on the seats (slide valves). This leaves a free running engine that does not cutoff early and create vacuums in the cylinders that drag exhaust gases into the valve chests and cylinders. It also does not compress these already hot exhaust gases into hotter gases at the ends of the exhaust strokes and cause the cylinder lubricant to burn up.

The various water brakes were intended to take advantage of the high compression ratios in steam engine cylinders. However, a steam engine is not a compressor, it is an expander. The fatal flaw with all the compression brakes was that they never modified the cylinders and valves enough to really make the locomotives efficient compressors. The primary problem rests with the adiabatic expansion line on the indicator card. This is a thermodynamically reversible process! If you reverse the piston and go back to its starting position (without opening the exhaust port) you will compress the steam right back to its starting pressure and temperature at cutoff. However, the piston does not stop at cutoff! It keeps squeezing the steam until it gets to the end of the stroke. If you follow the asymptotic expansion/compression line it keeps getting steeper and steeper. By the time you get back to the end of the stroke the steam pressure in the cylinder is far above the pressure and temperature in the boiler or superheater. Why does this happen? Because the object in the steam engine is to reduce the excess clearance to a minimum -- something on the order of 10% of the swept volume. This means you are decreasing the volume the trapped steam occupies by a factor of 10. As the volume decreases the thermodynamic laws tell you the pressure and heat content is going to go up at an increasing rate. This is why most water brakes caused so much machinery devastation. They were simply too crude to adequately prevent severe overpressurization and blistering temperatures in the cylinders. Your explanation that the engineer had to monitor the boiler water valve the cylinder cocks and the reverse lever suggests there were no limits short of sliding the drivers or blowing out the cylinder heads.

I am fairly certain the Mechanical Department guys in Denver thought the water brakes were delivered from heaven. But, the Master Mechanics who had to keep the engines out on the road probably kept dossiers on the damage these things caused until the evidence of abuse was so great the ivory tower in Denver could persist no longer and the order came out to discard them. I have heard stories of D&RGW engines coming into terminals with the paint all blistered off their cylinder saddles from the water brake heat produced at train speeds on the heavy hills. Remember power is a function of speed. Braking power is no different than motive power. As the speeds increased the ability of the INSULATED cylinders to dissipate the heat of compression was too puny and huge amounts of heat would build up if the brakes were operated too aggressively. Lazy engineers who were not too good with the air brakes probably pulled the reverse lever back further instead and just let the engine burn itself up while thinking about their next beer at the Green Frog Saloon.

There are really two types of pressure-volume diagrams. They are the indicator diagram (card) which is based only on the swept volume of the piston in the cylinder. This is what most people see when they look at locomotive indicator cards. The other one is the Rankine diagram which includes the excess volume added to the swept volume. The Rankine card is most useful although almost nobody ever hears about this diagram anymore. The Rankine diagram can predict how high the compression pressure and temperature will go for a given set of conditions.

If you want a successful compression brake on your steam locomotive you first must develop accurate volumetrics that you can use to lay out a Rankine diagram. Then you can predict what kinds of pressure you can safely develop, how much braking power you can produce (within the limits of adhesion and speeds of operation)and how you can accurately control the amount of braking effort so you can actually use it for train control (the C&TS drifting valve is only good enough to get a light helper off Cumbres Pass - it is far too crude to be useful or safe for train control).

Once you know what kinds of pressures you want you then develop how much hot water mass in the cylinder will produce the desired compression at the end of the stroke. You can replicate the diesel engine Jacobs brake scenario by installing, say four precision pneumatic injector valves on each end of each cylinder's admission port. Each one of these valves will inject precisely the right amount of water to achieve 25% of the desired compression pressure. All four valves will give the engineer maximum braking power. Now the engineer has finite control that has limits - he cannot blow the cylinder heads off the engine or slide the drivers with a heavy train.

Next you install timed relief valves with large flow coefficients in the cylinder heads. Before the pistons get to the ends of their strokes with the teeny weeny excess clearance you open the cylinder relief valves so they break the pressure peaks and exhaust the hot compressed steam to atmosphere (up the stack) before it has a chance to push the piston back and return the stored energy to the train (the opposite of retardation - a runaway!). The hot compressed steam will also take the heat of compression (braking energy) with it and exhaust it to the atmosphere. The throttle will be closed and the reverse lever will be centered (losses due to lead will be neglible at working speeds). Cylinder oil will be delivered directly into the cylinders and valves much the same way it is now. But, the much lower pressures and temperatures will not destroy the lubricant as much as the old water brakes did.

This type of water brake will operate much the same way a dynamic brake operates on a diesel because, after all it too is a "dynamic brake". It will have the same benefits and limitations. In other words it will not replace the air brake, it will supplement it and make operation on heavy grades much safer.

I have posted many times on this and other bulletin boards about the water brake. It seems to be a lightening rod. I love posting about it because it is so badly misunderstood. It also shows that without a knowledge of principles and good engineering practices most steam engine operators are doomed to simply replicate all the bad history they should be leaving behind.

If anyone is seriously interested in a really good compression brake on their steam locomotive I would be happy to take a retainer and produce one for them. Of course, once you get the water brake going you will reduce wear on your brake shoes and increase wear on your engine's running gear because it will now be working hard going both directions. That is why I put my Green Velvet Cylinder and Engine Lubricants website address below. I can help you minimize running gear wear too.

Bill Petitjean

http://www.steamenginelube.com
petitinc@nwlink.com

Bill,

A couple of points, if I may. First, compression braking certainly is hard on the machinery, especially compared to wearing out brake shoes on trailing cars, but as to why the water brakes were removed from the engines now used on the C&TS, this point is invalid, since they still use compression braking to get down the hill, only now they are compressing 600 degree smoke, instead of 212 degree water vapor. I canÂ’t believe that this is an improvement. Remember that it has been reported that the Rio Grande continued to use water brakes on its first string standard gage power until the end of steam in 1956.

Second, IÂ’m not sure I follow your description of the valve events taking place with the valve gear working in the opposite direction to the rotation. Remember that the steam edges of the valve are now the exhaust edges, and vice versa. In an engine with lead, at no time would the piston be compressing against a blind cylinder, as the valve is open to the steam chest until past dead center, and able to take advantage of the cushioning volume of the steam chest, dry pipe and superheater. Look at a Zeuner diagram, and follow the events around the parameter in the opposite direction to normal operation to see what I mean.

What would be the compression stage of a normal cycle would, with the valve gear reversed, become an expansion stage, tending to counteract the braking effort for that period, but no more than normal compression counter acts the power stroke, as you pointed out. Such is the built in inefficiency of your standard 1st generation steam locomotive. Any efforts to overcome that deficiency would be better spent installing a cam operated poppet valve system which could be programmed to give efficient braking as well. DonÂ’t hold your breath until someone hires you to do that in this day and age.

As far as not being fool proof, what on a 1st generation steam locomotive is? Opportunities for damage and destruction abound from one end to the other. Proper use of a water brake would just be one more item for the engineer to be instructed on, and then entrusted to his instinct for self preservation, and fear of the road foreman.


kelly@strasburgrailroad.com