Air pressure questions


I finally found my books! I got the formulas from my copy of The Pipe Fitter's and Pipe Welder's Handbook by Thomas W. Frankland.

Cylindrical Tanks

C=capacity in gallons
D=diameter
L=length

When measurements are in inches:

C= D x D x .7854 x L divided by 231

When measurements are in feet:

C=D x D x .7854 x L x 7.48

Formula for volume of a sphere:

V= volume

D3= cube of the diameter

V= D3 x .5236

Example: What is the volume of a sphere whose diameter is 4"?

V= 4 x 4 x 4 x .5236 = 33.5104 cubic inches.

Divide cubic inches by 231 to covert to gallons.

Cubic feet x 7.481 = gallons.

Hope this works for you.
 
dave1905 said:
What exactly are you trying to simulate that would affect model operations? I have a feeling you are spending a lot of time figuring out something that has no real impact on anything a modeler would model.
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I am writing a software that simulates the controls of a real train for a model. It works in conjunction with JMRI (and runs in any web browser, just like a normal website) and thus I need to accurately model all the physics of the locomotive.

Does that make sense? It's kind of hard to describe, so I can clarify if I said something confusing.
 
Because what you are proposing is going to be a matter of perception to any user i'e. what each individual would consider is appropriate, taking George's example of 10mins, in HO scale (if my calculation is correct) that would take 6.8 seconds, roughly about the same time as it takes to get the start-up sound to settle back to an idle.
 
tootnkumin said:
Because what you are proposing is going to be a matter of perception to any user i'e. what each individual would consider is appropriate, taking George's example of 10mins, in HO scale (if my calculation is correct) that would take 6.8 seconds, roughly about the same time as it takes to get the start-up sound to settle back to an idle.
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Not even that. He's asking about charging the main reservoir. The only time you have to charge the main reservoir is if the locomotive is dead and the entire air system has been drained. Probably a locomotive spends about 99% of the time with the main reservoir charged (or being charged). From an operator's perspective its a non-event. If an operator has to wait for the main reservoir to charge then something is wrong or its the first move of the day and the locomotive has been shut down for hours.
 
Good news:

I was not able to find the dimensions (or any info, really) for the reservoir in an F-unit, but I was able to get dimensions of the reservoirs on a GP7, which I can "fudge in". I got them from the Wikipedia page on the GP7, which talks about the modification that some owners did where they put 4 air tanks on top and replaced the original 2 air tanks underneath with a steam generator for passenger service. Conveniently, it gives dimensions for both, so I was able to use those. I got that the two underside air tanks add together to make a total capacity of 46.7882 cubic feet.

I also mostly sorted out the programming for the compressor and solving for pressure of the tank, which is in large part due to the help from this thread. Thanks guys! I included a screenshot of the "dashboard" gauges/indicators, which I think are really coming together. These gauges are for an F7-A, but the software is being built to work with any locomotive you "install", much like a traditional train simulator.

szh0A9M.png
 
That's about a 350 gallon tank or tanks equivalent to 350 gallons. It would take a lot of air to charge an air line on a 100 car train.
 
k4kfh said:
Good news:

I was not able to find the dimensions (or any info, really) for the reservoir in an F-unit, but I was able to get dimensions of the reservoirs on a GP7, which I can "fudge in". I got them from the Wikipedia page on the GP7, which talks about the modification that some owners did where they put 4 air tanks on top and replaced the original 2 air tanks underneath with a steam generator for passenger service. Conveniently, it gives dimensions for both, so I was able to use those. I got that the two underside air tanks add together to make a total capacity of 46.7882 cubic feet.
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Not quite. The space underneath the frame was used for a water tank to supply water to the steam generator. The steam generator is in the short hood on the nose of the unit.

I also mostly sorted out the programming for the compressor and solving for pressure of the tank, which is in large part due to the help from this thread. Thanks guys! I included a screenshot of the "dashboard" gauges/indicators, which I think are really coming together. These gauges are for an F7-A, but the software is being built to work with any locomotive you "install", much like a traditional train simulator.

szh0A9M.png
Click to expand...

Engines don't have a tachometer (no engine rpm), engines don't have a fuel gauge in the cab (its a sight glass, or maybe a dial, on the side of the fuel tank).

They have a speedometer, main reservoir pressure, locomotive brake pressure and trainline pressure, and an ammeter. the trainline pressure is the one the engineers use to determine the brake settings, the main reservoir just tells them if the air compressor is working. There is no light for the air compressor, it goes on or off automatically. For model purposes the main reservoir pressure doesn't really tell the model operator anything. Unless it or the air compressor fails, it really isn't used in the actual train operation.
 
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Since really of all the stuff you have created, I would really only need the speedometer, the rest are not really essential to the over the road operation. The fuel gauge is checked once at the beginning of the shift/trip. The engine either has enough fuel to make the trip or it doesn't. Unless the train dispatcher makes other arrangements, the engine doesn't leave the terminal unles it has enough fuel, then the service track staff has to explain why they put out an engine without enough fuel. When the engine gets to a fueling location, the engines are fueled.

Based on what you have produced so far, I don't think you have actually seen a real engine cab or what the actual controls are or look like.

What you need is a combination brake pipe and brake cylinder gauge, a combination equalizing and main reservoir gauge, an ammeter, and a speedometer (optional).
The lights are for wheel slip, dynamic brake warning, and PCS Open.

You can find operator's manuals for diesel engines on web. Here's one for the EMD F7. It might help you avoid wasting your time building stuff that really desn't matter.

http://users.fini.net/~bersano/english-anglais/EMD-F7.pdf
 
Not quite. The space underneath the frame was used for a water tank to supply water to the steam generator. The steam generator is in the short hood on the nose of the unit.
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Sorry, I typed that from my phone and off the top of my head, guess I was remembering wrong.

The fuel gauge is checked once at the beginning of the shift/trip. The engine either has enough fuel to make the trip or it doesn't.
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I knew the fuel gauge wasn't in the cab, I just put it there because I didn't want to fight with making a whole different section of the program just for that one gauge. If it proves to be a hassle I can move it.

Based on what you have produced so far, I don't think you have actually seen a real engine cab or what the actual controls are or look like.
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You're pretty much right. I've been on the passenger side of an F7 and an ALCo RSD-1 when I was younger, but I didn't pay as much attention to the controls as I should've.

What you need is a combination brake pipe and brake cylinder gauge, a combination equalizing and main reservoir gauge, an ammeter, and a speedometer (optional).
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I understand most of these, but there are a couple I'm not familiar with. I'm assuming brake pipe is the brake pipe for the whole train, and there's not one for just the locomotive that I don't know about. The brake cylinder gauge though...is that for every brake cylinder on the train somehow, or is it just for the ones on the locomotive? And I understand the main reservoir gauge, but what is "equalizing"? Also I knew I needed an ammeter, but I haven't figured out the math to get how many amps I am drawing, so I haven't added that gauge yet. If anyone knows that math I would love some pointers in the right direction.

The lights are for wheel slip, dynamic brake warning, and PCS Open.
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Wheel slip is pretty self explanatory. Dynamic brake warning I'm guessing is a warning that the resistors for the dynamic brakes are overheating, but correct me if I'm wrong. From my brief reading on the internet, PCS open only occurs when you apply the emergency brake, and it just reduces all engines in the consist to idle until you reset the switch.

Am I understanding this correctly?
 
Dave 1905 is right about the main engine reservoir. It's always fully charged except when the engine is dead or your charging a train. I meant charging up 10 car reservoirs. That takes about a minute a car. Brewster, NY use to have yard air where all the cars in the yard were always fully charged but over the years to many leaks in the system etc. made it unworkable. You had to charge train when you coupled on and that took about 10 minutes for a 10 car train.
 
There isn't really a "formula" for amps for the engine itself. It depends on the train weight, whether the train is going uphill, downhill, is accelerating or decelerating, and how much power is available. You can't say that just because the train has 10 loads and is in throttle position 5 its drawing X number of amps. If you are doing solely a computer simulation you can control where the train is and know the grade, tonnage, curvature and tractive effort available and then calculate how much power you need to move the train. If you are doing a simulation on a model railroad the trick is knowing where the train is and what its doing.

Brake pipe is the train line and brake cylinder is the engine brakes.
 
dave1905 said:
There isn't really a "formula" for amps for the engine itself. It depends on the train weight, whether the train is going uphill, downhill, is accelerating or decelerating, and how much power is available. You can't say that just because the train has 10 loads and is in throttle position 5 its drawing X number of amps. If you are doing solely a computer simulation you can control where the train is and know the grade, tonnage, curvature and tractive effort available and then calculate how much power you need to move the train.
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For all intents and purposes I am doing a computer simulation. The only thing I won't be able to know (until I get occupancy detection) is grade/curvature. Everything else, basically an unlimited amount of data about each locomotive/car in the train, will be available. You can think of this as a train simulator game that happens to use a model railway for video instead of a virtual model. The computer program is doing all the "thinking" just like it would for a normal train simulator, only difference is it's telling the model to move instead of the virtual train to move.

That said, can you tell me how I would calculate amps in an ideal situation where every piece of information I need is available? Chances are I can get all of the info one way or another.

Thanks again for your help.
 
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