Santa Fe used Swing Brakemen on the First District (Cajon Pass).
They went on duty at San Bernardino and rode eastward to Victorville, where they got off the train. (The Engineer, Fireman, Conductor, and two Brakemen went on to Barstow.) They caught a westbound train, first in, first out, and there was a swing Brakeman for every 15 cars (at least that's the number I remember). They had to ride out on the cars from Summit to San Bernardino. They turned the handles on the required number of retaining valves to High Pressure position as the train passed through Summit, going from car to car on rooftop running boards. Coming into San Bernardino, they turned the handles on the retainers back to Direct Release. Sometimes the Swing Brakemen would use an empty ice bunker on an empty reefer as shelter in winter.
Retaining valves retain a certain amount of air pressure in the brake cylinders of cars when the brake pipe pressure increases (which would normally release all brakes). In the days before dynamic braking, trains had to descend from Summit on 7 miles of 3.2% grade and 20 miles of 2.2% grade, on air brakes alone. And the early dynamic brakes were better than none, but nothing like the dynamics they have today. Additionally, steam and early diesel locomotives were not equipped with pressure-maintaining brake valves, so the brake pipe pressure was always slowly leaking down and increasing the braking effort when the brakes were set for a long time, as on long mountain grades. Eventually, the train would stall if the braking effort were not reduced periodically.
The Engineer, because of the retaining valves being in use on the cars, could move the brake valve to Running position and recharge it, reducing, but not releasing, the train brakes, Then he would reapply the brakes. Setting and releasing in cycles ("cycle braking") was possible only due to the retaining valves, and thus the Swing Brakemen had a definite purpose.
Around 1954, Westinghouse Air Brake Co. came out with a pressure-maintaining version of its 24-RL automatic brake valve, and a kit to convert older non-pressure-maintaining 24-RL brake valves. So, by 1955, trains descending Cajon Pass could go down on a two applications*, which could be maintained for the entire distance, and the use of retainers was discontinued around 1960. However, Swing Brakemen were required by union agreement, not by law, and that did not end in California until 1964.
* One application from Summit to Cajon (3.2%) with a 10-minute wheel cooling stop at Cajon, (during which the Swing Brakeman turned some of the retaining valves back to Direct Release); and a second application on the 2.2% from Cajon to San Bernardino. In reality it usually did not work that way because there were several passenger trains, both UPRR and ATSF, and a freight train hardly ever avoided taking siding at least once between Summit and San Bernardino. But two applications would do the job under ideal circumstances.
