Brake Here: An Introduction to Transition Era Freight Car Brakes (AB/K)
Been thinking about older rolling stock recently. Id like to model some truss rod and ‘survivor’ cars that looked more at home in a blurry 1920 photo compared to a freight house with a diesel in 1956. These older pieces of rolling stock have always been my favorite. Anyway, there's a major catch that comes with them - and its that many were banned from interchange in 1953. Why? Because it was unprototypical to see the car in 1953. jokes aside, it's actually because of their braking system. If a car somehow survived the truck bans of the early 30's, the billboard bans of the late 30s, or catching on fire, its final woe would be the brake system. And for a railroad to rebrake a car then it must really be worthwhile. Many early wood and smaller cars did not make the cut. They’d be retired soon anyway. However plenty survived. Many had their brake system rebuilt well before 1953 in postwar shopping anyway, as the road knew the cars were valuable enough for service through the next decade.
It was July 1 of 1953 that anything but an AB brake system was banned from interchange. Prior to 1933 when the AB brake system was introduced freight cars were built with a version of the ‘K’ brake system.
This hit some smaller roads hard, many liked the per diem revenue they got from cars roaming the national system. The coal roads typically couldn't care less in many cases as their direct shipment of coal to port wholly on home rails was generally unaffected. This bought them time to gradually upgrade the worthwhile cars.
I've taken it upon myself to attempt on explaining what these various transition era brake terms mean:
K brakes (Pre 1933). First - In railroad terminology, the "K" in K brake (the Westinghouse K-Series freight car air brake) does not stand for a specific word. Instead, it is simply the letter designation assigned by the initial manufacturer -Westinghouse Air Brake Company- to this specific generation of equipment. It was a major innovation for the early 20th century and was one of the first systems to allow for graduated release. A very simple system that combined a ‘Triple Control Valve’ (which was in charge of 3 major things: charging the air reservoir, applying the brakes when pressure drops, and releasing them when pressure is restored), with a reservoir and cylinder in a single compact unit.
There were two versions of the K brake design setup:
KC: K Combined - This refers to setup where the primary components i.e. the Triple Control Valve, air reservoir, and brake cylinder - were physically integrated into a single, combined unit to reduce piping joints (and therefore cost/maintenance) under the car. The release valve was on top of the cylinder. KC was the norm until the introduction of AB systems and found on most cars.
KD: K Detached - The brake cylinder is separated from the air reservoir and control valve.
The KD system was often called a "split K" and was designed to fit railcars that lacked the space for a single bulky unit. It was frequently used on hoppers and drop gons, where space under the frame was limited.
AB brakes (introduced 1933): AB stands for ‘Automatic Balancing’. The name highlights the two main features of its design: an ‘A’utomatic service portion and a ‘B’alanced emergency portion.
Unlike the older systems that combined components, the AB system features three distinct parts: the 4 Action Control valve, the brake cylinder, and a two-part reservoir which separates service and emergency air supplies for faster response times. The AB brake system is the foundational standard still used on the majority of North American freight trains today.
AB control valves feature a 4 Action Control Valve which means: Quick Service: (When the engineer applies the brakes, the valve quickly vents a small amount of brake-pipe air locally at each car. (Brake pipe air is the compressed air that fills the continuous metal pipe -the ‘train line’- running the entire length of the train), Full Service: (After the quick service action initiates, the valve opens a direct path from the car's internal auxiliary reservoir to its brake cylinder). Quick Release (Air quickly dumped), and Emergency (Valve opens wide to tap into separate, dedicated "emergency reservoir" air).
On steam locomotive tenders it varies but the tenders have their own cylinders, reservoirs and do not typically have their own control valve. Instead, the braking force for the tender (in 99% of cases) is supplied and controlled directly by the locomotive's main air brake system such as a Westinghouse 6-ET.
I remember as a kid when I first read about the AB brake ban I figured it meant that the ‘AB’ implied the car had brakes rigged to both the A and B end of the car. But what did I know!
So, if you model pre July 1 1953 I think you should have a few cars in your train with K style brakes. Bonus if they're older reefers, wood boxcars etc.
I marked up some photos with the unique components of the different braking systems highlighted. These photos are random photos showing the unique setups however the markings are my own original markings. If you own the original source photo and wish for it to be removed please contact.
Rob Perez
