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| Re: SMEE (245865) | |||
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Re: SMEE |
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Posted by randyo on Tue Apr 25 18:52:25 2006, in response to Re: SMEE, posted by BIE on Tue Apr 25 07:11:54 2006. Actually, Jeff H had it expressed most accurately. In WABCO nomenclature, the first letter of the acronym described the method used for normal sevice braking, the second letter indicated if it was to be for a motor or a trailer car, the third letter denoted the type of automatic braking device used for the activation of the automatic service and/or emergency brake. On cars equipped with electro - pneumatic brakes, a letter "E" was added at the end. Thus on BMT BUs and derivative car types, the brake designation would be AML: a for automatic service braking, M for the motor cars (although the proper designation for trailer cars would actualy be ATL) and L for a type L triple valve, which was used to allow passage of air from the auxilliary reservoir into the brake cylinder during applications and from the brake pipe back to the auxiliary reservoir and the brake cylinder to atmosphere during releases.Over the years, the various types of triple valves developed into more sophisticated devices known as either "universal Valves" or "control valves" but their functions remained basically the same. On electro - pneumatic systems, there were several types. AMRE was used on IRT Hi-Vs and Flivvers and allowed the brakes to be applied electrically by having magnet valves apply and release the air directly to and from the brake cylinder when the brake valve was in the appropriate position. The drawback to this was that in the event of an electrical failure, the pnuematic brakes would remain relaesed if the M/M were calling for a service application since the electric service positions were pneumatically release or "charging" positions.. To avoid any, problems, In the event of a failure, pneumatic brakes would apply in emergency if the EP circuit failed while the electric brake key was engaged. If the elect. brake key were removed, the emergency feature would be disabled and the M/M would then be able to operate pneumatically only. The later AMUE (U for Universal valve usually type UE5) system combined the elecric and pneumatic service positions on the brake valve so that even in the event of an electrical failure, the pnuematic brakes would continue to apply and so the emergency application feature was not needed. On streetcar and interurban systems, where short 2 or 3 car trains wouldbe operated, a brake system called SME (no electric) was used where straight air applied directly to the brake cylinder was used for normal service braking, but a brake pipe was included for emergency applications only. This system. however, was not very useful for longer trains. During the 1930s, there were brake systems developed, superimposing a combination of electro - pneumatically applied straight air for normal service applications and automatic braking for emergencies. On these earlier systems, the trainline straight air only funcioned electro - pneumatically, so that in the event of a failure, automatic braking had to be used. Also earlier combined Straight air systems had fixed positions on the brake valves requiring manual lapping to cut off the air when the desired pressure was attained. By the 1930s, "self lapping" brake valves such as the M-38 and ME-39 were developed so that desired SA pressure was achived by positioning the brake valve at the appropriate place in the "service range." By the late 1940s, a system was developed that allowed straight air to be applied directly both electrically and pneumatically, thus the added pneumatic servive brake was no longer needed and the former universal and control valves only functioned in emergencies and be came an "emergency valve." This system was referred to as "SMEE" for straight air service, motor car, emergency and electric and utilized the ME-42 brake valve which eventually was modernized into the ME-43. By the way, although they were competitors, WABCO and NY Air Brake used the same model designations and their parts were fully interchangeable. I don't know what kind of patent infringement implications there might have been ealier, but a NYAB rep once told me that current federal regulations require the parts to be fully interchangeable. Around 1965, WABCO upgraded the SMEE system and changed its designation to RT-2 "RT" standing for "rapid transit" and "2" for the second modification in that series. From the beginning of the SMEE/RT-2 systems, some properties had equipment that utilized a "cineston" controller in which the power and braking were combined in one unit controlled by a single operating handle. Of course, the state of the art developed to the extent that the EP applications no longer had to be energized from a brake valve but could be energized electronically from a controller in the M/M cab similar to the earlier cinestons and we had the development of the RT-5 system which uses the troublesome "P wire" to control the brakes and now the much improved RT-7 which while still totally electronic does not appear to be suffering from the same difficulties as the RT-5. |
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