@big train posted:Well, apparently there is a recognition that the braking force required for an empty car is significantly less than that required for a loaded car. The empty/load sensor identifies an empty or loaded car and regulates the air pressure to the brake cylinder accordingly.
Here's some links for anybody interested.
New York Air Brake (click through to the technical documents/component write-ups for additional info)
NYAB Technical Guide (has a schematic showing how the sensor is integrated into the brake system plumbing)
Wabtec Empty/Load top pageThere's also a slope sheet mounted sensor which serves the same purpose, although it seems specific to hopper cars.
I was wrong about how the sensor works. By default, the lever on the sensor does move closer to the truck sideframe as the loaded car settles on the springs, but it doesn't make contact with the sideframe at that point. Instead the lever is retracted when brakes are released, and extends to the sideframe when air is applied. How far the lever travels dictates how the air is proportioned to the brake cylinder. It obviously has further to go when the car is empty.
So in that sense, the device would in fact indicate by it's position whether brakes are applied or released. It's not the primary purpose, but it does happen by default.
What I'm curious about is why in both examples in this thread, the sensor levers appear to be extended, when there ostensibly isn't any air in the system. The Trinity hoppers in my photos are empty cars that have been stored without moving for at least five years. Even with the angle cocks closed, doesn't the air bleed off eventually?
If there is pressure held on the system and the line pressure is zero that pressure would be used to apply the brakes. That is how the failsafe works. But yes, eventually it will leak out. How long that takes depends on the seals on the individual car and a few PSI might remain for a long time. If you look at the truck cylinders (not attached to the handbrakes) and they are applied then either there is residual air pressure or there is something wrong with the brakes and that is why they are sitting there.
Got any more pics of the end frame areas?
