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Re: I think the engineer was trying to make up time
Author: Dr Zarkoff
Date: 10-14-2020 - 13:13
On the SP, the "E-brake", was an overlay (and add-on) to 8-ET which enabled it to operate the E-brake system on the cars. The locomotives were equipped with 8-ET, while the cars used the D-22-PTE brake system (also called "HSC"). The "electric brake valve" was an M-36 self-lapping straight-air valve, which was developed for traction use. This operated an electro-pneumatic controller on the locomotive, which was a double-ended piston with two electric switches in the middle. When the M-36 valve was moved to an application position, it pressurized one end of the controller via the control pipe. This moved the piston one way, closing one of the switches to energize the application magnet valves on the locomotive and all cars in the train. The other end of the piston was connected to the straight-air pipe (essentially "to the brake cylinders"), and when the straight-air pipe pressure rose to the point of being equal to the control pipe, an internal spring moved the double-ended piston back to mid-position, or "lap", which de-energized the application magnet valves. A brake release consisted of the opposite actions, except that when the double-ended piston moved the other way, the other switch closed to energize the release magnet valves.
WABCo's use of "straight-air pipe" with the HSC system is a bit confusing, because rather than being pressurized from the locomotive, the pipe was pressurized by the magnet valves on each car in the train, drawing air pressure from each car's auxiliary reservoir. Use of the auxiliary reservoir in this way did two things: 1) it kept the automatic brake system in step with what the E part was doing at any given moment so that if the E part suffered a failure, the automatic system could immediately take over at the same braking rate, and 2) it provided almost instantaneous pressure build up in the pipe throughout the train, which is not possible if done only from the locomotive. Straight-air controlled from directly the locomotive fails after train length exceeds about three 40 foot cars; the HSC system is designed for 24 car trains of much longer passenger cars.
The air being sent "to the brake cylinders" was in reality sent to a relay valve, which drew air pressure for the brake cylinders from a supply reservoir on each car. There were actually two relay valves, because the second one was stepped to regulate brake cylinder pressure according to train speed, as determined by a speed governor:
speed: braking ratio
0-20: 100%
20-40: 150%
40-65: 225%
over 65: 250%
The speed governor ran off 64v, which is the primary reason for the extra dynamo on the locomotive (the cars had 32v electrical systems).
A good view of GS-4 brake controls can be found here: [spdaylight.net]
Scroll down to the last GS-4 view. The M-36 valve can be seen in font of and slightly below the L-8 automatic.
Source: WABCo Instruction Pamphlet 5064 Sup. 4,The "HSC" Brake Equipment with No. 22D Control Valve (Southern Pacific Railroad), 2-1937. While this is SP-specific, the basic system functions are the same for the E-brakes used by other railroads.
As I mentioned earlier, the M-36 brake valve was developed for traction use, and the Electroliners at IRM and Rock Hill Furnace are equipped with them, along with the same electro-pneumatic controllers. There appear to be no automatic air brake provisions, so the liners probably use relayed straight-air.
Variations on the locomotive equipment were an M-40-A self-lapping automatic brake valve, which merged E-brake functionality into the automatic brake valve, and the type of locomotive distributing valves: #22, #24.
By the 1960s, all the RRs had removed the E-braking capabilities because of maintenance costs.
A word of caution on what the old heads said: the only time I recall ever hearing one to be correct is when he said "you can't rush Mr. Westinghouse".
The more rapid the control of air pressure throughout a train, the more responsive the brakes are. I once ran an 88 car train of empty coal hoppers which were all equipped with ABD-W, and its braking responses were virtually the same as with the Electroliner at IRM, which is only four cars long. (No US freight braking system has graduated release).
WABCo's use of "straight-air pipe" with the HSC system is a bit confusing, because rather than being pressurized from the locomotive, the pipe was pressurized by the magnet valves on each car in the train, drawing air pressure from each car's auxiliary reservoir. Use of the auxiliary reservoir in this way did two things: 1) it kept the automatic brake system in step with what the E part was doing at any given moment so that if the E part suffered a failure, the automatic system could immediately take over at the same braking rate, and 2) it provided almost instantaneous pressure build up in the pipe throughout the train, which is not possible if done only from the locomotive. Straight-air controlled from directly the locomotive fails after train length exceeds about three 40 foot cars; the HSC system is designed for 24 car trains of much longer passenger cars.
The air being sent "to the brake cylinders" was in reality sent to a relay valve, which drew air pressure for the brake cylinders from a supply reservoir on each car. There were actually two relay valves, because the second one was stepped to regulate brake cylinder pressure according to train speed, as determined by a speed governor:
speed: braking ratio
0-20: 100%
20-40: 150%
40-65: 225%
over 65: 250%
The speed governor ran off 64v, which is the primary reason for the extra dynamo on the locomotive (the cars had 32v electrical systems).
A good view of GS-4 brake controls can be found here: [spdaylight.net]
Scroll down to the last GS-4 view. The M-36 valve can be seen in font of and slightly below the L-8 automatic.
Source: WABCo Instruction Pamphlet 5064 Sup. 4,The "HSC" Brake Equipment with No. 22D Control Valve (Southern Pacific Railroad), 2-1937. While this is SP-specific, the basic system functions are the same for the E-brakes used by other railroads.
As I mentioned earlier, the M-36 brake valve was developed for traction use, and the Electroliners at IRM and Rock Hill Furnace are equipped with them, along with the same electro-pneumatic controllers. There appear to be no automatic air brake provisions, so the liners probably use relayed straight-air.
Variations on the locomotive equipment were an M-40-A self-lapping automatic brake valve, which merged E-brake functionality into the automatic brake valve, and the type of locomotive distributing valves: #22, #24.
By the 1960s, all the RRs had removed the E-braking capabilities because of maintenance costs.
A word of caution on what the old heads said: the only time I recall ever hearing one to be correct is when he said "you can't rush Mr. Westinghouse".
The more rapid the control of air pressure throughout a train, the more responsive the brakes are. I once ran an 88 car train of empty coal hoppers which were all equipped with ABD-W, and its braking responses were virtually the same as with the Electroliner at IRM, which is only four cars long. (No US freight braking system has graduated release).
