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| Re: Photos: BMT ''C'' Types (882960) | |||
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Re: Photos: BMT ''C'' Types |
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Posted by Jeff H. on Wed Jan 6 23:01:56 2010, in response to Re: Photos: BMT ''C'' Types, posted by Steve B-8AVEXP on Wed Jan 6 08:44:46 2010. That's because the R1-9 and D types used an A1A or A1 (respectively)variable load unit. Inside of that unit is a relay valve. The UE5 does not directly control brake cylinder pressure, but instead charges and discharges a dummy brake cylinder known as the Volume Reservoir. The variable load unit then acts as a proportional relay valve to establish a brake cylinder pressure proportional to the volume reservoir pressure and to the car load weight. The release sound of an R-9 is in 3 parts: 1) A short spurt of air released from the bottom of the exhaust valve filling piece. This is the exhaust/cutoff valve moving from the electric to the pneumatic position. 2) A sustained blow of air from the same port. This is the pneumatic release of the volume reservoir air. 3) A louder sustained blow from the variable load unit. This is the self-lapping portion of the variable load valve releasing the actual brake cylinder air. D-types are almost identical. IRT Lo-V cars never had variable load equipment. Therefore the 3rd part of the above sound is missing. BMT steels had a much earlier version of variable load. Instead of using a proportional relay valve, it used a convoluted piece with seven internal chambers that would be connected to the auxiliary reservoir volume in various combinations so that volume is added proportional to the load weight. Increasing the AR volume means lowering the equalization point between BC and AR pressures. A separate feed valve-like mechanism was used to limit emergency cylinder pressure. |
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