If the enginner doesn't want or need to brake the train, and wishes to merely coast, he can shut the throttle and the engine will coast freely if the Johnson bar is in the correct position. However, with the snifter valves closed, it will begin to brake the train due to back-pressure on the pistons. So, a snifter valve must be opened if the engineer truly wishes to coast on level or slightly descending track for any substantial distance.
http://en.wikipedia.org/wiki/Snifter_valve
This from http://www.catskillarchive.com/rrextra/toc.Html
PURPOSE OF RELIEF-VALVE ON DRY PIPE.Should the throttle-valve close so tight that the compressed air from the cylinders can not pass into the boiler, there is danger of bursting the steam-chest or some part of the, steam-pipes. The compressed air will lift most of the throttle-valves far enough to prevent any great danger from this source. In some engines a relief-valve is secured in the dry pipe, which provides a passage for this compressed air. When the cylinder-cocks of an engine are opened when the motion is reversed, they form an outlet to the compressed air, and also admit air to the sucking end without letting the piston draw air so freely through the nozzles. Many cylinder-cocks are now made so that they will open automatically to permit the piston to draw air through them. The reversed engine will stop nearly as well with the cylinder-cocks opened as when they are closed, and it is much more easily handled with the cocks opened. Where the cocks are kept closed, the rush of hot air from the smoke-box laps every trace of oil from the valve-seat, and a heavy pressure — frequently above that of the boiler — is present in the steam-chest. When the engine stops under these circumstances, its tendency is to fly back; and an engineer has some difficulty in controlling it with the reverse-lever till a few turns empty the chest and pipes.
USING REVERSE-MOTION AS A BRAKE.Numerous attempts have been made to utilize the reversed engine as a brake for stopping the train, and even by this means to save some of the power lost in stopping. Chatelier, a French engineer, experimented for many years on this mechanical problem. He injected a jet of water into the exhaust-pipe, which supplied low-tension steam to the cylinder, instead of hot gas or air coming through the smoke-box. This was pumped back into the boiler on the return stroke. Thus the act of stopping a train was used to compress a quantity of steam, converting the work of stopping into heat, which was forced into the boiler and retained to aid in getting the train into speed again. Modifications of this idea produce the car-starters that pass so frequently through our Patent Office.
As a means of conserving mechanical energy, the Chatelier brake was not a success; but, in the absence of better power brakes, it met with some applications in Europe. Some of our mountain railroads use it, under the name of the water-brake, as an auxiliary to the automatic brake.
-Crandell
Thanks everyone for your time and expertise.
There's nothing wrong with your locomotive -- real steam engines stopped making the chuffing noise when coasting.
Ed
When a engineer decelerates a steam engine he is cutting off the steam to the cylinders. This lets the weight and momentum push the engine along in effect like putting your car in neutral. A steam engine drifting along can be very quiet. There may be some flange noise or on an older steamer some rod knock will be heard until all the drivers are in unison. Your Hudson represents a more modern locomotive that has been fitted with rods and bearings that have very close tolerances that will not have too much rod knock. Some locos were fitted with roller bearings on the main rods that had no rod knock unless something was broken.
Pete
I pray every day I break even, Cause I can really use the money!
I started with nothing and still have most of it left!
Ed,
are you sure chuff sound COMPLETELY cuts out, or is just a little bit quieter? If it ain't completely cut out, then this is OK, because in this way locomotive imitates the real situation (for example, when going upgrade, sound must be louder then when going downhill, and the chuff sound also).
Hrvoje
I have just received my Paragon2 Hudson from FDT. Looks great and I love the way it runs. However, when I decelerate, the chuff sound cuts out. Does anyone know what cv I have to change to fix this?