[PRCo] Re: All--Electric___Control___Circuits

[Boris Cefer]

> > Boris Cefer wrote:
>
>
> > When electric brake actuators are adjusted at shops
> > (heavy maintenance), they use a dynamometer to adjust
> > them at 55 kilogram pull.     Don't know exact value in
> > lbs required by WABCo specification.
>
> Too Easy To Overlook.......
>
> THANK  YOU,  BORIS.......

You are welcome. All of you.

> for the excellent explanations of drum brake operations
> with facts and figures.     Gives a wonderful base
> for understanding the mechanics behind the operations
> and dispels the myths and rumors.
>
>
>
>
> >> From: "Fred Schneider" <fschnei at supernet.com>
>
> >> Regarding variable rate drum brakes:  drums were
> >> generally used only in conjunction with extended
> >> dynamic brakes in North America,
>
> > I don't know much about GE, but Westinghouse equipped
> > PRCo 1700s had their drum brake control circuits
> > designed so as to obtain 3 different braking rates.
> > Wiring diagram shows it clearly. And we had the same
> > arrangement on earlier equipment.
>
> Are you able to calculate the braking effect and
> grades on which the drums would hold the car at these
> 3-different rates?

I forgot to mention. Each rate (on all-electric) is for one particular brake
pedal position; in parked position (pedal half way) the drum solenoids have
no power which means the maximum braking effort.
I think if you find drawings with some important parameters, I can calculate
it. I hope.

> Do you think this would be common with all
> WABCo actuators or does it also depend upon the drum
> brake itself?

I don't know details of other actuators. But if the principle of it is that
braking effect is reached simply mechanical way by means of a spring and
releasing is done by a magnetic coil which acts directly against the spring,
then the actuator can provide particular range of braking effect. But
remember that NOT all coils, magnetical cores, main springs and pasive
friction between moving parts in mechanism are identical on each actuator an
d if you give the same lower voltage to all four actuators on a car, the
braking effort of each particular brake will slightly differ. And the
difference between particular brakes increases with drum shoe wear.

> You mention that Ostrava  *had*  same arrangement
> but apparently does not now.     What does Ostrava use
> now and why the change?

The difference you mean is supposedly in that older equipment had 3 drum
brake and 3 track brake rates. Newer cars are different - 2 drum brake rates
only. Also the track brake circuits are different, ech truck's brakes work
separately. By only slight pressing the brake pedal below park position you
will actuate those on rear truck only (they receive full voltage), when you
press the pedal more, then also the front truck's brakes will be lowered.
The newest equipment has an electronic disc brake control, but the actuators
are identical, only the spring adjustment is different.


> >> I was not aware that anyone had variable track brakes.
> >> you simply don't use them in normal service because they
> >> cause excessive rail wear, particularly at stops.
> >> A good operator simply doesn't push the pedal more
> >> than half way down.     We also don't want the
> >> passengers to be alarmed by hearing the emergency buzzer.
>
> Passengers would not understand the emergency
> buzzer  --  it was barely audible for the operator so
> it doesn't cause alarm.     In fact, the emergency buzzer
> sounded like the passenger buzzer for Air-Cars! :)
> Once talked my mother into walking up to 42-wye to board
> the car.     When I told her the operator put the 12 into
> emergency approaching Biltmore coming downhill she just
> shrugged her shoulders, said:  "Oh," quite unenthusiastically,
> and went on reading her magazine!
>
> Believe that a moderate amount of track brake
> was pulled in during  *Full--Service*  braking on PRCo cars.
> Putting the car in Service-Latch (as it is called on
> some properties  --  pressing brake approx half way and
> then releasing deadman which locks brake in place)  was
> NOT  full-service  --  *Full__Service*  went a little further
> on braking and there was a physical barrier where pressure
> increased going beyond that point  --  and beyond that
> point is emergency.
>
> With all the hills in Pgh there would be tremendous
> wear on drums or brake shoes doing the final stopping and
> a moderate amount of help from the track brake would be
> in order.
>
>
>
>
> > GE policy?     Why not.     But again - I don't know GE.
> > Westinghouse 1700s had 4 (F-O-U-R) rates of
> > track brake actuating.     Gives sense to you?
>
> Would you be able to describe operations with
> the 4-different levels of track brake?     What part
> is used for normal braking?

This only depends on how much you press the pedal below park position.
That's all, there are resistances in drum brake coils circuit which are
sequentially short-circuited by gradual pressing of the pedal. OK. Parking
position is about 68° rotation of brake controller, first rate begins at 90°
with 9.75 ohm resistance in the circuit, on 94° begins the second rate by
means of short circuiting part of the resistance and 1.75 ohm remains in the
circuit. Next change is on 106° and 0.5 ohm is now in the circuit. Last
change is on 116° where the remaining resistance is short-circuited and
track brake coils receive full voltage, about 37 V DC when battery is being
charged from MG.
Supposedly not very easy to hit each particular rate, because only small
fragments of inch are between particular rates. Full pedal travel is 6"
which is 136° rotation of controller cams. You can easily calculate those 4°
of controller. Almost ZERO inch.

You can use the moderated braking when you catch a slip when stopping at car
stop and don't want to kill people on bord by flooring the brake pedal. Full
track brake braking is quite strong, even on a slippery rail where it is
added to a low braking effect of slipping wheels.
When you floor the brake pedal, also sand is automatically dumped on rails.

Normal braking is up to park position (parking position is full-service
braking), means half way of pedal = 3" or 68° on brake controller. So, no
track brakes in normal braking.

> Was watching the cars at the Dormont wye (normal
> Summer--Time duties) and one 17 had track brake come on
> as car made final stop backing up.     Doors were open
> (against rules) for backing move and operator had put
> brake in Service Latch and removed feet from pedals.
> Several seconds later the track brake  *shut-off*  and
> started dancing as the springs lifted it off the rail.
> No emergency buzzer but operator had probably pushed it
> into  Full--Service  to get it into  Service--Latch or
> Park! :)
>
>
>
>
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> Jim
>
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