Air consumption

Main Train Horns
1

How would one go about calculating how much air their horn uses?

Lets take my setup, 5 gallon tank at 200psi, 1/2" brass and valve, and 3/4" hose.

If my nathan k3 takes the pressure from 200 down to 150 in 4 seconds, how much air is it using on average.

I realize it decreases as pressure decreases, but lets say on average?

Im pretty good with math but not sure how to go about this one, mainly trying to figure out how much air is actually in the tank when its compressed. After that its just dv/dt.

2

Well damn I should have just thought about it a little more.

Simple application of boyles law (Assuming the compressed air has already cooled).
PcVc=PaVa (c= compressed, a= atmospheric).

The conversion from gallons to cubic feet is 1 gallon = 0.1337 ft^3

So fully chargerd there is
(200*)(.6684)/14.7 = 9.0939 ft^3

at 150psi,
(150)*(.6684)/14.7 = 6.8204 ft^3

so dv/dt which is volumetric flow rate in CFM,
(9.0939-6.8204)/4/60 = 34.1 ft^3/min

Anyone concur?

3

I know that 7.4805 gallons = 1 cu ft.
That means 1 gallon = .1337 cu ft.

4

Ah, right, thats what I used since 5*.1337 = .6684

5

I know I saw a thread where somebody listed the consumption of a K3 or K5.
It would be interesting to see if that number is close to yours.
Maybe I’ll hunt for it…

6

I kept thinking 4 seconds was too long, and boy I was right. I am actually going from 200 to 145 in 1.3 seconds! Although this was done with a stopwatch while sitting still, im convinced its not that fast when im actually driving since air is being rammed into the horns since they face forward, but I digress.

5*.1337*(200-140)/(14.7*4/60) = 125.93 ft^3/min which seems much more accurate.

Using this chart, http://www.fuelslut.net/ihost/files/123/AirchimeKSeriesChart.jpg, as a guide, 125CFM through a K3 is really effin loud :smiley:

7

The cubic feet of air in a tank depends on the pressure too. The higher the pressure the more cubic feet.