Water Brakes

[Anonymous]

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

[csxengineer98]

please define "water brakes"

[edblysard]

Hi Hank,
Checked the post there, I think what they are talking about isnt really brakes, in the true sense of the word. On piston driven and some turbine driven steam ships they had a water injector system to inject, under pressure, a cool water mist into the piston on it's compression stroke, or exhaust stroke. And, as water is "harder" to compress than steam, it increases the pressure on the piston, slowing it down slightly. With turbines, it cooled the gas/steam before it entered the turbine. This is done only when you have to make a quick change in the rotation of the screws, say from 20 turns per minute to 5 tpm in preparation to reversing one or both of the screws or during a sharp turn or a docking move, and when you wi***o slow down, or trail one of the screws.
Used on locomotives, its the equivlent of steams dynamic brakes, by injecting a cool water mist into the exhaust side, it creats a resistance to the piston on the exhaust stroke, but allows the engineer and fireman to keep the steam pressure up, as when going down grade, but having to be prepared to attack a up hill grade soon after. It fell out of favor with American railroads quick, because the cool mist also exited along with the spent, and now even cooler steam, and cooled the superheater down, not a trade off railroads wanted. And if the engineer mis-judged the amount of water to inject, it could damage the piston, both by increasint the compression beyond the tolerance of the piston and the added water condensed and could score the cylinder. Steam pistons, on locomotives and ships, are not designed to compress anything, but instead, are designed to be "pushed" by expanding steam.
When I find the book this is from, I will post it for you. My dad was a lifer in the USN, and had a fairly large selection of books and service manuels on ship designs and power plants.
The locomotive reference was in one of them, I just cant remeber which one, yet.
Stay Frosty,
Ed

[csxengineer98]

0h ok... that is a water brake... i thought it was some new kind of braking system someone was tring to come up with... like useing hydrolic brakes such as in a car for stoping a train...
thanks for clearing that up for me ed
csx engineer

[Anonymous]

Ed, a wealth of information indeed! We here in aviation use water injection for more power and not as a brake. I would have never thought of it used to decrease power but you sound like you know what your talking about. Now if we go into ADI (anti detonation injection)or what we call wet or water take off I will have to explain my laughter and use your post for backup.

[Anonymous]

The Harrier also uses water to keep the engines cool when it is hovering.

[foamer4000]

Ed,
The Rio Grande used water brakes on all of its steam until, the very end. (with the excepyion of leased units). Robert La Massena published an article in trains magazine a ways back. I recall that he said; The wet steam was taken from the boiler and ran to the valve chest thru a 3/4 inch pipe. That steam was then released into the valve chest during the piston exaust stroke, cushoning the piston. The cylinder cocks were open during the water brake operation. This prevented the ever unpopular removel of the cylinder caps! If you ever have an opportunity to watch some video of old Grande steam, the water brake operation can be seen in down grade footage. It is evidenced by a clean stack and little puffs of steam released from the cylinder cocks.
David
Stay frosty Unionhead!

[edblysard]

Remember as a kid watching some of the SAC bombers taking off, they left huge clouds of white "smoke" behind them. Asked my uncle, (army air corp, then USAF) why these "smoked" so much, and the fighters the Navy flew didnt. I think he said they injected water into the combustion chamber to increase the turbine pressure?
Clue me in, that was 35 years ago.

[edblysard]

Next timee I get a chance to watch, I will look for that. Did they leave the cylinder drain cocks open all the way, or did they have a system to decide how far? I remember reading on some steam locomotives, it was standard practice to leave the drains open when you started up in cold weather, to prevent the condensation from building up. When the cylinders warmed up enough to vaporize the condensate, they were closed.
Sound right?
Stay Frosty,
The Unihead Ed

[Anonymous]

White smoke? Usually when water injection is on the smoke is very dense black on a pure turbojet. Anyway, water is used to lower the density of the air which makes for more power (lets you pack in more air). It also has the nasty problem of erroding the internal engine parts like the turbine wheels. The water is actually interduced in the compressor stage.

[bfsfabs]

Dan, "Lower the density of the air" ?? I'd a thought the idea would be to RAISE the density of the air. In order to stuff more into the same given space. Or is there something about turbojets I don't understand. I have only dealt with reciprocating engines. Automotive.

Lowell

[foamer4000]

Ed
It is standard practice to have the cylinder cocks full opened when starting a steamer, regardless of outside temperature. Water will naturally condense in the cylinder when a locomotive is stationary. I belive during water braking the cylinder cocks are not opened all of the way, by the apperance in the vidio, I do not know this for a fact.
Just to throw this out. In power plant turbines, the steam is condensed on the exaust side. This reduces back pressure and increases efficency. Not water injection, or water braking, but good trivia!
Take care Unionhead Ed
David

[Anonymous]

you are right! The only thing that had lower density when I wrote that was my Brain! It is to raise the density, the mass air flow, through the engine. I was thinking of density altitude when I wrote that statememt. Sorry, again you are right.