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| Re: Brake Valve pr0n Re: LIRR MP-54 #1149 and its ME-23 brake valve (485011) | |||
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Re: Brake Valve pr0n Re: LIRR MP-54 #1149 and its ME-23 brake valve |
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Posted by Jeff H. on Mon Sep 3 02:38:59 2007, in response to Re: Brake Valve pr0n Re: LIRR MP-54 #1149 and its ME-23 brake valve, posted by Bill West on Mon Sep 3 01:45:28 2007. All AMUE equipment is going to have at least 4 fingers in theelectric portion of the motorman's brake valve, i.e: Supply, Release, Apply, Emergency. On some forms of the ME-23 brake valve, a 5th finger was provided. The NYM/BMT used this for the infamous "#12" wire. I will now attempt to explain the circuit as best as I can from memory, without reference to the schematic. The designers were evidently concerned with the ability to "plug" the motors for emergency braking during a loss of traction power. Ordinarily, with low-voltage WH-AB or GE-PC control, there is a relay, called the line relay by WH and the potential relay by GE, which drops out the group when traction power is lost, and forces it to go back to the initial notch and wait for power to come back on. The purpose of this circuit is to avoid the inrush current when the car comes back on after a long third rail gap. Since 0 current was flowing through the field coils, there would be almost 0 counter-EMF, and thus a very large surge if the group were already wound up to a high notch. On streetcars, it is a well-known technique to use emergency dynamic braking by flipping the reverser and placing the motors in parallel. This works even if there is no traction power, because it creates a dynamic brake loop wherein the motors act as generators and cross-feed each other, with virtually 0 load resistance (and thus a very heavy brake). To make this possible with automatic control, it is necessary to provide a means of bypassing the line/potential relay functionality. Thus, IIRC, on AB and D type equipment, placing the line switch cutout switch in the cab to OUT and placing the brake handle in emergency energized the #12 wire, which picks up a relay in each car bypassing the contacts of the LR/PTR. Then by placing the master controller in parallel, the group will run up to full parallel with the line switch dropped out, effecting emergency dynamic braking. I do not believe the difference between ME23 and ME30 has anything to do with the number of fingers. IIRC it was a fairly arcane difference in the size of the porting in the full release position, one of the valves being designed to charge faster than the other. Also, the M23/ME23 provides a "Brake Cylinder Exhaust" port on the pipe bracket, the purpose of which is to make "Holding" both an electric and a pneumatic hold position, on those brake schedules where the universal or triple valve exhaust is piped back up to the brake valve. This arrangement was seen on interurbans but never used on any NYCT equipment that I can recall on any of the 3 companies. IIRC the ME30 did not have this port. |
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