[PRCo] Re: PRCo___Dreaming - - - - - The__Next__Hit__Song!!(:->)

[Fred Schneider]

Jim Holland wrote:

>
>
>         Do the Red Arrow PCC-like streamliners actually employ dynamic
> braking?

Certainly they did, but the distinction was in how the dynamic and air were
controlled.

PCC cars (except in Europe) had a spotting circuit which positioned the
accelerator drum or GE KM controller arm for maximum dynamic braking at all
times.  When you go for dynamics on a PCC, you get them.  Then the brake
pedal is depressed, you get instantaneous dynamic braking.  No waiting.
Just like the hydraulic brakes on your automobile.   The PCC was great
compared to any air brake car in that respect.

The Red Arrow cars did not have the spotting circuit.  Therefore, when you
go for brake, the accelerator drum bridge has to rotate until it finds the
proper resistance position for maximum dynamics.  You loose a couple of
seconds up front when you need brake!

I also said air (or spring applied drums on an all-electric).  On a PCC car
there is a lockout relay.  When the dynamic brake current fades, the lock
out relay allows the shoes or drums to come on.  Of course only at the tail
end of the stop.

The Red Arrow cars have a blending valve.  Air generally comes on when you
first tramp on the brake pedal because there is no dynamic or insufficient
dynamic effort to hold the air off.  [Sidebar ... if you go from full
acceleration instantly to full brake you will get instant dynamics.  You
only get air first after coasting for a while.]  But air is compressible.
Any one who drives a truck or bus understands that you also don't get air
brakes instantly.  The brake pipe lines and the brake cylinders need to fill
with air.  [There is an especially long delay when you have older streetcar
equipment or railroad cars with 12" diameter brake cylinders.]  So you loose
a second up front until you get air.  Then the dynamics come on and you
loose the air.  Then the dynamics go off and the blending valve is again
supposed to bring the air back on.  Again, a measurable delay.   My daughter
has a great expression from her teen age years (she's 38 now) ... "it
sucks."    The gyrations are not particularly nice on wet or greasy rail.
But it did save production costs and it also allowed the car to coast
freely.   None of this is a problem if you are working entirely on
private-right-of-way but there is no such word as entirely.

fws