Railcar brakes

[Perry Babin]

1. Do each of the handbrakes have to be reset manually after they're set? Or is there some threshold of air pressure that resets/releases them when it's reached?

 

2. Do handbrakes set the brakes on both trucks, or only on the one closest to the wheel/control used to set the brakes?

 

3. For the main airbrakes, is the actuator a piston in a cylinder or is a balloon type of diaphragm?

 

4. For the air system used to apply the brakes (the one including the on-board tank for each railcar, beyond and including the triple valve), what's the (rough) percentage that would leak down (after a day, a week) without a connection to the locomotive?

[jeffhergert]

1. Hand brakes have to be released manually.

2. Depends on the air brake equipment being used.  On WABCO equipment hand brakes only set the truck nearest to it.  Usually seen on hopper and tank cars.  New York Air Brake equipment sets the brakes on both trucks.

Easiest way to tell is to look where the brake chain goes to.  If it goes to a lever on the truck, that end only.  If it goes to a rod that connects to the brake rigging at the brake cylinder (the brake piston points to the hand brake) it sets both trucks.  

3. Brakes | The Railway Technical Website | PRC Rail Consulting Ltd (railway-technical.com)  Scroll down to the "operation on each vehicle" section.

4.  Know way to say precisely.  It depends on many viariables such as condition of the equipment and ambient air temperature.  I've seen cars that have been stored for a few months with the air brakes still applied.  I've seen cars that the air has leaked off within an hour.  

You'll still hear "triple valve" being used.  It's common for informal discussion in the field.  The link I provided uses the term.  The current proper term is now control valve and that's what's used in manuals and rules.

Jeff

[adkrr64]

Perry Babin

1. Do each of the handbrakes have to be reset manually after they're set? Or is there some threshold of air pressure that resets/releases them when it's reached?

Yes. Hand brakes have nothing to do with the air brake system per se. They are devices that mechanically hold the brake shoe against the wheel, whether or not there is air on the car or not. They are both manually activated and manually released

 

Perry Babin

2. Do handbrakes set the brakes on both trucks, or only on the one closest to the wheel/control used to set the brakes?

 

For anything I have worked with, the hand brake acts only on one truck. I have worked with a few cars that have hand brakes at both ends, but more the exception than the rule.

 

Perry Babin

3. For the main airbrakes, is the actuator a piston in a cylinder or is a balloon type of diaphragm?

 

Everything I have seen/ used is a piston in a cylinder. Not sure what you mean by "baloon type". There are different types of setups where the there is a single cylinder that applies all the brakes on the car (body mounted) or applies the brakes on one truck (truck mounted). The former is almost always the case on freight cars; the later is more often seen on older passenger cars (newer passenger cars have disc brakes, and I am not entirely sure of the mechanisms they employ).

 

Perry Babin

4. For the air system used to apply the brakes (the one including the on-board tank for each railcar, beyond and including the triple valve), what's the (rough) percentage that would leak down (after a day, a week) without a connection to the locomotive?

 

This will vary greatly depending on a number of factors, including:

• Length of time since the brake system was cleaned and serviced (COTS date).
• Air temperature: Gaskets and fittings usually shrink when cold, and thus will be more prone to leaking in colder weather

These systems can actually be quite robust. I've seen cars hold air and keep brake cylinders in the applied position for several days at a time. Even saw it last year on an old flat car that gets used only in the yard. Its last COTS date was in the late 1970's. Yet the brakes still worked and the system was still holding enough air to keep the brake sylinders applied more than 24 hours after it was cut off.

[SD70Dude]

To elaborate a bit on question 2, most freight cars have a single brake cylinder and rigging from it to all four axles.  On these cars the handbrake will apply on all the wheels.  

Cars with truck-mounted air brakes are different.  Their brake cylinders are located inside the truck frame and there is mechanical connection between trucks.  The handbrake only applies on the B-end truck on the majority of these cars.  There are exceptions like the old Canadian government grain car fleet (the 'Trudeau hoppers'), which have truck-mounted air brakes but also have a brake beam running the length of the car, which is there solely for the purpose of getting the handbrake to apply on both trucks.  

There is no specific answer for how long railcar air brakes will remain applied for, it is best thought of as a probability calculation with the following conditions.  Any one car could leak off at any moment, but the vast majority of cars will hold their air for hours and many will hold it for days, with some lasting even longer as in Jeff's example.  

[tree68]

I've had cars that wouldn't hold a set for more than a few minutes.  Obviously, they needed attention...

You may find this an interesting read on railroad air brakes.  It's a little dated in some respects, but I refer to it as a primer on the subject:

http://www.railway-technical.com/trains/rolling-stock-index-l/train-equipment/brakes/north-american-freight.html

 

[Perry Babin]

It's not really important but I should have written diaphragm type instead of balloon type. I was thinking that they would be less likely to leak down than a piston in a cylinder.