Valuable Values


This page serves half of this entire guide's purpose. As I said in the author's note at the beginning, one of my goals with this guide is to make hard-to-find numbers/formulas easy to find. I've spent countless hours searching for obscure formulas, reservoir dimensions, pipe diameters, operating pressures, and other important numbers that nobody seems to have. Consequently, I've gathered all of these values in one central location to save everyone else the trouble.


  • Tractive Effort: T = 2650 * (nP/V) Source
    • Where T is Tractive Effort in Newtons
    • n is an efficiency coefficient (for the F7-A it is ~.85)
    • P is the output horsepower
    • V is the velocity in km/hr

General Pneumatic Equipment#

  • Main Air Reservoir Volume
    • EMD F7-A : 46.7882 cubic feet
  • Main Air Reservoir, Compressor Cutoff Switch Pressures (Typical)
    • Upper Limit: 140psi
    • Lower Limit: 128psi

Westinghouse Brake System Equipment#

  • Train Brake Pipe
    • 90psi to 120psi typical pressure, set by the feed valve
    • 1 1/4 in. diameter
    • Brake signals normally travel at ~500ft/sec
    • Emergency brake applications travel at ~900ft/sec
    • ~50ft of pipe per car (derived algebraically)
    • Approx. 3.3 gallons of pipe capacity per car
  • Auxiliary Reservoir
    • 2500 cubic inches (10.5 gallons)
    • Air in this reservoir is directed, by the control valve, into the brake cylinders during a service brake application.
  • Emergency Reservoir
    • 3500 cubic inches (15.5 gallons)
    • During emergency brake applications, this reservoir combines the auxiliary reservoir to give an increase in brake cylinder pressure. Also, during release of the brakes, this reservoir helps recharge the auxiliary reservoir or the brake pipe depending on the type of control valve used.
  • Brake Cylinder
    • 630 cubic inches (2.7 gallons)
  • Equalizing Reservoir
    • 220 cubic inches (approx. 3 quarts)