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>Can anyone explain the functions of so many connections? Many other railroad GP photos show that their units had but 3 MU's per side. Is the difference between roads how the units were used. Its been 35 years since I've worked with the older loco air brake MU systems but I'll give it a try... From the inside out on each side you have the... 1. Main Reservoir Equalizing hose. This hose connects all the locos' air reservoirs together so all can supply air. 2. Actuating hose. This hose is what bales-off the locos' independent brakes. When the engineer makes an air brake set using the automatic (train) air brake the brakes set not only on the train cars but also on the locos themeselves. In most cases you do NOT want the loco brakes to apply so the engineer depresses his independent air brake handle and that puts 45 psi into the MU Actuating hoses which causes loco air brake valves to release the locos' brakes. 3. Application & Release hose. Sometimes called the "Independent Application & Release" hose or just the "A&R". When the engineer moves his independent brake valve handle into the application zone a variable air pressure from 0 to 45 psi (depending upon how far he moves his brake handle) is put into the A&R hoses. Some locos use a maximum of 45 psi brake cylinder pressure. Some locos use 72 psi max brake cylinder pressure. On locos that use a 72 psi maximum brake cylinder pressure there is a 1.6x multiplier valve that increases that hose pressure by 1.6 times. I other words if there is 45 psi in the A&R line then 45 x 1.6 = 72psi in the cylinders. Basically the A&R line is what applies and releases the loco independent brakes. The above 3 lines are the now standard hoses seen on all locos. Older locomotives used a different loco brake system. Instead of the Actuating hose and the A&R hose they used a single Brake Cylinder Equalizing hose. The engineer's independent brake valve put a 0-45 psi air pressure into the Brake Cylinder Equalizing hose and that applied the loco brakes on all trailing units. The 4th hose from the center is that Brake Cylinder Equalizing hose. During the change-over from the BCE design to the Act/A&R design railroad's locos needed to be able to MU with either type of air brake. Thus locos from the late 1950s to the mid 1960s had hoses for BOTH systems. The 5th hose, the outer-most one, was the loco sanding hose. The early locos had air operated sander control and thus need an MU hose to tell trailing units to sand the rails. Later locos have electric sander control which is communicated to trailing units via the 27 pin MU jumper cable. Some locos came from the builders with all 5 hoses and some locos had the extra hoses and valves added by the RRs. __._,_.___ Posted by: runextra@gmail.com __,_._,___ |