Air pressure questions


K

k4kfh

Member
I'm building a simulation application and I need to know some things about locomotive air equipment.

  • What is the standard pressure for the main locomotive reservoir?
I'll add more questions later as I get to them. Thanks guys!

P.S. If you're interested in this software, it basically gives prototypically accurate controls to model trains. Check out my GitHub page to learn more.
 
Every one I've run has had 120 psi. Trainline pressure is less, generally depending on type of equipment. Passenger usually has a higher trainline pressure than freight.
 
Okay. Does the compressor kick on the instant it drops below 120psi, or does it wait till like 100psi or some other slightly lower level to "fill it up" again?
 
Normal main reservoir pressure is 130-140 PSI . Compressor kicks in about 130 and cuts out at 140. I have heard some railroads run higher pressures.
 
So does anybody know the volume for main reservoirs on locomotives (an F7 is what I'm trying to simulate) or know where I can find it?
 
I guess the volume would have to be determined by the number of gallons of water it would hold. Something that's not compressible. I guess you would have to measure one then make a calculation.

George
 
If you can find the dimensions for a tank, I can give you the formula to figure the capacity. Or I guess I could figure it for you since I'm a nice guy!:)
 
Being that I know nothing about locomotive specs, I guess that brings me to my next question.

Engineers, what's the typical dimension for a locomotives main reservoir, or specifically an EMD F7?

Burlington Bob, if you could give me the formula, that'd be great. I want to feed a capacity into my software, so I'd like to make an easy tool for people to find the capacity given dimensions. Thank you!!

Sent from my SAMSUNG-SGH-I337 using Tapatalk
 
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I just realized that there is another option. If nobody knows dimensions/volume, but somebody knows about how long it takes to pressurize the main reservoir on an SD45, we can make that work. According to Mr. Al Krug, a compressor on an SD45 puts out about 255cfm @ 900rpm. So if someone knows about how long it takes to go from 0 to a given pressure (and someone can provide the RPM during that time) I can figure it out. This is a bit of a "clunky" way to calculate it, but even in the EMD manual for the F7 I can't find the volume or dimensions of the main reservoir, so it may be the only way to figure it out.

So, anyone who has ever driven an SD45, about how long does it take to pressurize the main reservoir, to about what pressure, and at what engine RPM?

Thanks guys!
 
900 RPM is full throttle/ RUN 8. It would pump up pretty rapidly at that rpm.

From 0 to 140 psi you would also be charging the complete air system, air brakes and everything else that uses air as well as the main reservoir. There is a lot of associated piping involved that creates volume also.
 
fire5506 said:
900 RPM is full throttle/ RUN 8. It would pump up pretty rapidly at that rpm.

From 0 to 140 psi you would also be charging the complete air system, air brakes and everything else that uses air as well as the main reservoir. There is a lot of associated piping involved that creates volume also.
Click to expand...
Can you put a number on "rapidly"? Are we talking 30 seconds, 30 minutes, or what? Thanks for the reply though.
 
I couldn't tell you because I have never seen one go from 0 to 140 at full throttle. At full throttle from 130 to 140 probably takes about 5- 10 seconds. I'm going from memory here.
 
Sorry I haven't got back to you with the formula for figuring capacity of a tank. I can't find my copy of The Pipefitter's Blue Book anywhere. I know it's here somewhere! Coming off a three and a half month run of work, one at a nuke in northern Illinois and the rest at a coal burner 20 miles from the house with long hours and time spent living on the road up north means that sometimes I'm a little less than organized. Add remodeling a room and that means that I've got stuff scattered all over God's Little Acre and half of France.:eek:

You can figure the volume of a cylinder and the volume of a sphere and come pretty close but then you have to convert cubic feet (or inches) to gallons. Gets complicated. The formula in the trade books is a lot easier to use, as well as more accurate. But if you can't get any dimensions I guess it's a moot point. I will continue to keep an eye out for it as I go about my chores here at home.
 
Volume of a cylinder is V= πr[SUP]2[/SUP]h. π is pi or about 3.14, r[SUP]2 [/SUP]is the radius times itself (radius squared), h is the height. If you make this calculation in inches, divide that result by 144 to get the cubic feet. Take the resulting figure and multiply by 7.5 gallons (approx) per cu. ft. (water) to obtain the approximate answer. Although as Burlington Bob states "if you can't get any dimensions I guess it's a moot point". Remember that this is only applicable to the reservoir and doesn't include air lines, cylinders and other associated plumbing on the individual cars, some of which may or may not have remaining air in them. You're on your own there. Hope that this helps a little.
Willie
 
Air tanks have bell ends to contain the pressure, thus the reason for needing the volume of a sphere. It isn't quite a perfect sphere but the formula would be close enough if you included the calculations for one, along with the volume of a cylinder.
 
Okay let's see Volume of a sphere is 4/3 piR cubed (I can't figure superscripts) so the volume of a tank with spherical ends would be V= (4/3πr cubed) + πr[SUP]2[/SUP]h where r is the radius of the tank and h is the length of the straight portion. Just remember to keep measurement units (ft, in, meters) consistent. I don't think the conversion from cubic inches to cubic feet is 144. That would be for square ft (area) for cubic feet it would be 1728 (12x12x12)
 
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.
 
I don't know if this would help you but back in the 70's it took 2 EMD FL9 engines 10 minutes to pump the up braking systems for 10 passenger cars.
 
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