| BN E9Am 9906 at Roosevelt Road in Chicago, Illinois on July 13, 1983, photo by Chuck Zeiler. This train has just left Union Station and is approaching Canal Street, so he is likely in the process of conducting his running brake test. I have had previous discussions with Karl Rethwisch, a former CB&Q/BN Locomotive Engineer, and he revealed the characteristics of the 24RL brake schedule as applied to the CB&Q E-units. I inquired if the rebuilt E's retained the 24RL brakes, and here is his relpy:The M-K units came back to us with a replacement for the 24RL schedule called the PS68. After using the thing a few times I bestowed a name on it that would probably not fit well in most articles but did retain the letters PS. The intentions of the design was twofold; eliminate the need for two separate brake systems, and provide a means of recharging the air system much faster than was possible with a conventional brake system. Recharge is the term used when, after releasing the train brakes, the air that was used to apply them is replaced in order to bring the system back to a fully charged state. The air in the entire trainline is effected by an application and is reduced by an amount equal to the reduction made by the Engineer. This reduction in brakepipe pressure causes the control valves to allow reservoir air to flow to the cylinders and press the shoes against the wheels. After releasing the brakes the cylinder air is vented to the atmosphere and is, for purposes of brake 'health', lost. The air used in an application MUST be replaced in order to have air available for subsequent applications, hence, RECHARGE.The PS68 operated in a somewhat conventional manner as it related to brakepipe reductions and lapping. For this discussion, LAP is just like opening a sink faucet, filling a glass to your desired level and closing the faucet. In a brake valve, no air flows through it when lapped. The PS68 now departs from conventional brake valve design in that it adds a HOLDING feature to the positions available to the Engineer. As noted, when a brake valve is LAPPED no air flows anywhere, meaning that no air can be put into the trainline to replace that just used. HOLDING: After making the necessary brakepipe reduction and while waiting for the speed to reduce to zero, the brake valve is placed in the holding position. Electromagnetic valves on each car act to 'HOLD' the air pressure in the brake cylinders while, at the same time, allow air from the engine to flow into the brakepipe, thereby recharging it. I won't deal with the vagaries of this brake valve right now as it would add considerable length to this discussion. I'll say it was NOT my favorite brake valve. |