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Im´m no expert (forgot to mention it: proof me wrong, if I am), and I´d be gald if you could tell me what you mean with your last post, ragtimer
I don´t get, how replacement air should flow to the AR or the BC, if the BP has to be lower pressurized than the AR / BC for keeping the Brakes applied. there´s just no pipe for this replacement air to get there, if the triple valve is in apply Position. Also, how to get some air in tere, the pressure of the Input air must be higher than the one in the AR. That in turn would release the Brakes...
Markus,you really do not get it.If you reduce the brake pipe to zero in a Westinghouse single pipe system,the brakes are going to leak off pretty quick because there is no air supply to anywhere on the cars to keep the brakes applied because the replacement air for leakages must come from the brake pipe.If there is no air in the brake pipe....no replacement air!And you get no extra brake force than with a reduction to 64 psi!
To ll who were trying to explain it, and did it correctly: A member of ElvasTower Forum who has a book on this Topic published by Wentsinghouse Company ITSELF confirmed to me, thiese drawings are simple, but correct. (see here
So, to all: take a closer look on them and everything on normal operations will be cleared out.
And another Thing to "durable" air-brake applications: (don´t confude with normal operations!)
And as for a full Service application: Practically thinking, there´s no Advantage in reducing the BP further than to 64 psi, as that´s the pressure of full Service application and you qouldn´t get out more by reducing further. From a technical approch, a running locomotive would now try to maintain this BP pressure, so it doesn´t leak away. The pressure in the AR and BC, however, does nevertheless bleed off. Thus, the Reservoir (and BC) pressure will at one Point just naturally become lower than the BP, resulting in a release.
This implicates - no matter, if this is allowed or not on any railroad - that if you want to hold a Train for a longer time just with the air Brakes, one should reuce the BP to Zero, just to be sure. Remember: if the Reservoir leaks below the air line pressure, the air line then is higher than the Reservoir, causing the triple valve to go to release!
I think is not a matter of one pipe versus two pipe, but of triple valve system, with only the auxiliary reservoir ,versus "ditributor" system (also built by Westinghouse company) with auxliary and "command" (reference) reservoirs.
In the first case, as far as I know, the equilibrium is between brake pipe and brake reservois, in the secon case the equilibrium is between brake pipe plus brake cylinder and "command" reservoir; if I understand weel in the second case the auxiliary reservoir can be keep at brake pipe pressure (one pipe system) or at "constant" pressure (two pipe system). This is done to achieve the "inexhaustibility"requirement of the system. Inexhaustibility means that, during normal operation, when a train has his brakes released it has in the auxiliary reservoir enough air for at least one more brake application.
Vince,exactly what I said!!!!!.The engineer would not have reduced the brake pipe to zero because that way,it is guaranteed the brakes will eventually release because the brake pipe which is the source of air for a single pipe train is empty.The engineer would have made a set to give the maximum application (refer to Al Krug again) because any further reduction in brake pipe pressure gives no more application pressure. quote from his article:
But what happens if you make a 26 psi reduction from a 90 psi brake pipe? 90 minus 26=64 psi in the brake pipe. Remember the triple valve moves to the apply position and allows service reservoir air to flow into the brake cylinder until the service reservoir pressure lowers to equal the brake pipe pressure. As the service reservoir pressure flows into the brake cylinder the brake cylinder pressure rises. Because of the 2.5 to 1 ratio of volumes, when enough air has flowed into the brake cylinder to lower the service reservoir 26 psi the BRAKE CYLINDER PRESSURE IS 64 psi !!! (2.5 times 26 =64) This air came from the service reservoir which is NOW AT 64 psi ALSO. Since the reservoir pressure and the brake cylinder pressure ARE EQUAL no more air will flow into the brake cylinder.
This condition is called a FULL SERVICE brake application because even reducing the brake pipe further, below 64 psi, WILL NOT INCREASE the amount of brake cylinder pressure. Even if you reduce the brake pipe pressure to zero psi the reservoir and brake cylinder pressure will still be 64 psi., the same as it was with only a 26 psi reduction. This full service or "equalisation of pressures" occurs at 64 psi for a 90 psi charged system. It occurs at 71 psi for a 100 psi charged system resulting in higher full service brake effort. It occurs at 57 psi for an 80 psi charged system resulting in lower full service braking effort. The corresponding brake pipe REDUCTIONS are 26 psi for the 90 psi brake pipe, 29 psi for the 100 psi brake pipe, and 23 psi for the 80 psi brake pipe.
With the brake pipe at zero,whether or not the loco is "supplying" air,eventually all the air in the cars will leak away.If the loco is shut down the same applies,however the brakes were set.
>The air in the line being applied directly to the, brake shoes or whatever,
And this is clearly what I am trying to clear up.
The train pipe charges the Aux reservoir through the triple valve,
Then a reduction of air in the train pipe moves the triple valve to apply and the air from the aux reservoir applies the brakes.
Not to nit pick, but you didn't give a technical name for, and clear things up, what is actually being pressed against the wheels, or the hose for that matter that sends the air from the aux reservoir to those things that is actually being pressed against the wheels.
I don't know their technical names, and that is what my "whatever" was referring to...
That "hose" may leak air releasing the pressure from the "Brake Shoes" against the wheels.
>The air in the line being applied directly to the, brake shoes or whatever,
And this is clearly what I am trying to clear up.
The train pipe charges the Aux reservoir through the triple valve,
Then a reduction of air in the train pipe moves the triple valve to apply and the air from the aux reservoir applies the brakes.
Freight Cars do not require a locomotive to be attached for the brakes to be applied. Each car has a reservior air tank on them. When there is a LOSS or REDUCTION of air in the main brake pipe, then the reservior air tank releases whatever air is stored inside the tank to apply the cars brakes. This is why when the line BREAKS and/or a train seperates in to TWO or more parts while the train is in motion, the train will come to a sudden stop for safety reasons.
What the locomotive does, is to SLOWLY lower the pressure to apply the brakes a little bit, as the reservior air tank tries to maintain an equal amount of pressure with the pressure in the main brake pipe. If the pipe is LESS then there are MORE brakes. If the pipe is suddenly emptied, the brakes are fully engaged. Only if the pressure in the main brake pipe INCREASES will the brakes on the cars RELEASE.
Charging these reservior air tanks may be done by the main brake pipe, or a secondary air system. The idea is to keep these reservior air tanks fully presurized. If there is no air in them, then then brakes can not be applied.
The air in the line being applied directly to the, brake shoes or whatever, from the reservior air tanks may eventually leak out over time. This has nothing to do with the locomotives. The locomotives only affect the operation of the reservior air tanks.
I posted that link on the original thread.First thing I said was "read Al Krug's article on air brakes" or similar words.Whatever air brake system you are using,unless handbrakes are applied if the air supply to the train is cut by whatever reason,eventually the train brakes will leak off.
Sorry but that turns out not to be the case;
All The brakes will eventually leak off, bleed down and release even if the engine is connected and running. Why? Because the air tanks and brake cylinders on the cars are NOT recharged with the brakes applied.
Please remember that brakes are APPLIED by a train air line REDUCTION, NOT pressurized as some folks here are thinking. And a 'reduced pressure' air line simply cannot keep the brakes applied.
The brakes are held applied only as long as there is pressure in each cars air tank, the same tank that is recharged when the brakes are released and the train air line is pressurized. Do not confuse this car air resevour tank with the cars brake CYLINDERS! They apply mechanical force through the brake rigging/shoes only as long as there is sufficient pressure in the cars air resevour.
Remember that the train line is emptied when brakes are fully applied and you can't recharge anything to keep brakes applied from an empty air line.
As soon as the brake cylinders leak off over some amount of time, then no brakes.
That's why it's against the operating rules on every railroad to park a train with air only.
The single train line air pipe has TWO purposes it does in life:
1. APPLIES train brakes (by triggering the triple valve in each car) when air is RELEASED from the air line.
and
2. RECHARGES the train cars air resevours to RELEASE the train cars brakes.
The above applies to a SINGLE PIPE (Westinghouse) air brake system only! Used on US freight.
Twin pipe air found on passenger equipment operate differently, a completely different system. Don't confuse the two types.
I posted that link on the original thread.First thing I said was "read Al Krug's article on air brakes" or similar words.Whatever air brake system you are using,unless handbrakes are applied if the air supply to the train is cut by whatever reason,eventually the train brakes will leak off.
"ps: The auxiliary reservoir cannot be higher that the brake pipe else it will move the triple valve and apply the brake. "
I agree with triple valves, but with the "distributor" shown in the picture? Note that there are two reservoirs: one for pressure reference and one for air acuumulation.
Shows a simple picture of a wagon brake system.
As you may see, any loss of air from the brake pipe, will move the triple valve slide and allow the auxiliary reservoir to apply the brake.
ps: The auxiliary reservoir cannot be higher that the brake pipe else it will move the triple valve and apply the brake.
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