[PRCo] Re: Brake Shoes

[Fred Schneider]

None of the low-floor cars got dynamic braking.   They did, however,  
get a different brake lever ratio to improve brake performance at  
higher speeds. And they got brake lights worked by pressure switches  
in the air brake pipe.   In this case, improved performance only  
meant improved force on the brake shoes.

And Phil, you just touched on another subject regarding why those low- 
floor cars would be absolutely inferior on the streets today.

Let's assume you have a nine inch diameter brake cylinder and you  
have a six inch piston travel, then you need 381 cubic inches of air  
to fill that cylinder.  You need to fill it using a 1/2 inch pipe  
that runs from the air reservoir under the car all the way to the  
brake valve on the platform and back to the cylinder, a distance of  
about 45 feet or 540 inches.   It takes a hellish long time to charge  
that cylinder moving that volume of air that distance.  You will  
begin to feel a brake response roughly two seconds after you move the  
brake valve into apply.

But you automobile, because hydraulic fluid does not compress, give  
you an instantaneous response.  Dyanmic brakes, because electricity  
moves at 186,000 miles per second, is, for all practical purposes,  
also instantaneous.

But air brakes on conventional streetcars SUCKS.

The first time I was on one of those Gomac-built replica Birneys in  
Tampa I was astonished at how fast the air brakes applied.   It  
seemed almost instantly, like a bus or truck brake.  And the air  
tubing from the brake valve looked too small to actually work the  
brakes.    Later, when I was in their shop, I asked the  
superintendent if those cars used some sort of a relay valve to work  
the brakes.   His answer was yes, and he took me down in the pit to  
look at it.   The 1/2 pipe went directly from the air reservoir to  
the relay valve to the brake cylinder, a distance of perhaps not over  
two feet.   The relay valve was controlled for the platform valves  
through very small pipes about the size of soda straws.   Only a very  
small amount of air had to be moved to make the relay valve work and  
therefore it moved almost instantly, and the large volume of air  
needed for the brakes only had to move a couple of feet instead of  
charging a 1/2 pipe 45 feet long.   So the brakes applied almost  
instantly and they released almost instantly.   BUT, PHIL, I HAVE  
NEVER HAD THE PLEASURE OF RUNNING SUCH A CAR IN A MUSEUM.   I do not  
know that we ever built such a critter for street operation because  
we quit making cars with straight air systems in this country in the  
1930s.

Now, what do trucks and buses use.   Good question.   Glad you  
asked.   I've driven buses.   I've even driven tractor-trailer  
rigs.   But I've never bothered to investigate.   I guess it's time I  
do.   But the response rates are incredibly fast so I suspect that  
they also use some sort of a relay valve system.

++++++++++++++++LIFE OF BRAKE SHOES ++++++++++++

How often did brake shoes have to be changed.   I have never seen a  
chart that shows what is normal.   I remember John Horachek writing  
on the Electroliners on the Chicago, North Shore and Milwaukee  
Railroad.   John wrote that they changed out one truck truck every  
night in Milwaukee.   There were two trains and one got to Milwaukee  
every other night.   That meant that they had completely replaced all  
shoes every eight days.   They made two round trips per day ... that  
4 one way trips x 95 miles  x 8 days or = 3,040 miles per shoe.

You do not change all shoes the same day or you need a parachute to  
stop the car or train.   Why?   If you buy shoes for 26 inch wheels  
and you put them on wheels that have been in service for a while and  
they have worn down to 25 1/2 inches, then those brake shoes are only  
going to touch the wheel along from side to side across the middle of  
the shoe.   The rest of the shoe from top to bottom will not even  
touch the wheel.   It will take quite a few stops until the shoe  
wears enough that it contacts the wheel over it's entire surface  
area.   That is why the CNS&M changed out only 1/4 of the shoes every  
day every second day.

I remember going to work in Harrisburg one morning on a Penn Central  
or Pennsy or Amtrak schedule using City of Philadelphia or PSIC or  
SEPTA Silverliner that some dufus in Wilmington shops had changed  
brake shoes on the night before ... the ass hole had changed all the  
shoes at once.   You couldn't even stop that car with an emergency  
brake application.   The engineman was not particularly enthralled  
with the idiots in the shop.   How did I know?   Well, they all knew  
that I was also working for the Strasburg Rail Road.  I often rode up  
front with the engine crew.   In fact one night one of the engineman  
slapped my hand on the controller and backed off before I could stop  
him and I ended up running for 36 miles from Harrisburg to  
Lancaster.   (Sheee-it, I just went into Yellow Book.com to see if I  
could find that engineer ... no listing ... wonder if he died?)

City street service?   Have no clue.   I've heard Ed Amrhein bitching  
about shoes he put on the Peter Witt at the Baltimore Streetcar  
Museum a year before already needing changing but I think they were  
buying a very soft cast iron shoe.   If we wore one out in a museum  
environment in a museum, that would not have lasted a day in a service.

The best person to ask would be Elmer Van Dullen who is the retired  
shop superintendent of New Orleans Public Service / New Orleans  
Regional Transit Authority.   I cannot find the number in Yellow  
Book.com under New Orleans.   Lives somewhere out in the city's  
western suburbs.   Or maybe you can find his successor in the RTA  
shops.  You probably want to know how many car miles they operated  
last year and how many sets of shoes they used.   And if you find  
out, post it.   I want to know too.

The multiple unit single end low-floor cars (3750s, 5000s, 5100s and  
5200s had dynamic brakes that could be energized in emergencies by a  
separate controller.   The reason is simple.   In order to stop a car  
with drum controller (type K as in K-35 K-8, K-63, etc.) in an  
emergency if you have lost your air, you pull the reverse key in the  
direction opposite to the way you are going, kick the canopy switch  
(breaker) off, and then notch the controller up through the points.    
A four motor car will go into dynamic braking on point 1, a 2-motor  
car will not develop a brake loop until it is in the parallel  
points.   However, cars with remote control (GE type M, GE PC, GE  
PCM, Westinghouse AL, AB, HL, HB, VA) will not do this because the  
reverser is under the car and will only throw when you pull power.    
Because you have thrown off the canopy switch, you have no power.    
So you cannot create emergency dyamic braking.   The normal emergency  
procedures with such cars is to use power to buck them in reverse,  
i.e. put it in reverse and pull a point of power if you loose air.    
But Pittsburgh put a special dynamic brake controller on them for  
emergencies.   But they were not used in normal service.

++++++++++++++++++++++SPECIAL SAFETY FEATURES++++++++

Pennsylvania required required safety appliances like those on a  
Birney car after 1938 for anything operated in one-man service.   All  
of the low-floor cars still in service in 1938 had dead-man  
controls.   They did not, however, have the doors incorporated into  
the brake valve like the M28D valve used on a Birney and I'm not sure  
that the doors balanced if you went into emergency.   Some day when  
I'm running 4398 or 3756 I'll have to deliberately dump the air to  
find out.

fws


On May 17, 2008, at 2:46 PM, Phillip Clark Campbell wrote:

> Hello;
>
>
> Many of the low-floor cars were re-worked for faster speeds.  Did  
> they get dynamic braking or did they rely solely on brake shoes?   
> How often would brake shoes need replacement?  Were there any  
> special safety features on these cars?
>
>
> Phil
>
>
>
>
>