Re: AIR BRAKES 101.... was Re: RGS #20. Was: [HOn3] Division Point K-27 question

Earl Knoob

First off, there are no springs involved.  Truck air brakes use springs.  Railroads use nothing but air pressure to hold the brakes on a car.  If it leaked off, or someone bled off the car, it would roll free.  Your only recourse is to climb on the car and wind down the hand brake.  The hand brake uses mechanical pressure to pull on the brake levers to set the brakes.

This is why it is constantly driven into RR employees to never rely on the air brakes alone to hold a car stationary.  Always set the hand brake and/or chock the wheels so that it can't roll.

From: <> on behalf of Climax@... <Climax@...>
Sent: Thursday, October 8, 2020 2:20 PM
To: <>
Subject: Re: AIR BRAKES 101.... was Re: RGS #20. Was: [HOn3] Division Point K-27 question
Lets say a box car was left on a siding with a grade.  Now there is either a very slow leak or can someone come along and pull the bleed off rod and would that result in the brakes being applied through springs to not let the car roll, or would the brakes release and let the car roll?  If it did roll, and you jumped on the car to get to the Brake wheel, does that apply or release brake pressure. 
The triple valve is on an AB system while a K system did not have that feature of  triple valve?

-----Original Message-----
From: Earl Knoob
Sent: Oct 8, 2020 3:27 PM
To: ""
Subject: AIR BRAKES 101.... was Re: RGS #20. Was: [HOn3] Division Point K-27 question

When the brakes are initially charged up, 90 lbs of air pressure is sent down the brake pipe.  This air not only fills the brake pipe, but it charges up the auxiliary reservoir in each car.  There is a valve called the "triple valve" which connects the brake pipe, the brake cylinder and the aux. reservoir together.

Once the aux reservoir and brake pipe are fully charged, the brakes are functional.  To make a controlled "service application". The engineer releases air from the brake line.  This causes a pressure imbalance between the aux air res pressure (still at 90 psi) and the brake pipe (now something less).  The triple valve then sends air from the aux. reservoir to the brake cylinder.  Once the pressures equalize, the triple valve "laps" and stops the flow of air.  If more braking is need, more air is released from the brake pipe, again causing a pressure imbalance, letting the aux. res. to put more air into the brake cylinder.

To release the brakes, the brake pipe pressure is restored, the triple valve again recharges the aux. res. and the brake cylinder pressure is exhausted to atmosphere.  The retainer valve is placed in the brake cylinder exhaust line.  It is simply an either spring loaded valve or a dead weight valve, that holds air in the brake cylinders while the brake pipe and auxiliary reservoir pressure is restored.  Holding the air in the brake cylinders allow the brake to drag while recovering the pressures.

If an air hose breaks, all the air is lost from the brake pipe.  This creates a massive pressure imbalance between the aux res and the brake pipe.  The triple valve then dumps all the aux res air into the brake cylinder at once as an "emergency application".

In theory, the brakes would remain set until the brake pipe pressure is restored.  Or you can go to each car and pull the bleed off rod, which releases the air out of the aux res.  As the triple valve is in emergancy position, the aux res it is connected to the brake cylinder through the valve, so when the aux res air is drained out, so is the brake cylinder air.

Clear as mud, right?

From: <> on behalf of Climax@... <Climax@...>
Sent: Thursday, October 8, 2020 12:19 PM
To: <>
Subject: Re: RGS #20. Was: [HOn3] Division Point K-27 question

I always thought that the lack of air pressure set the brakes.  If a line rupture they cylinders would empty and as it did the brakes came on slowly.  Am I wrong?  If a car is set on a siding and some nitwit came along and released the air the brakes should set no matter what, unless someone is smart enough to burn the brake wheel to release them or does that only set them?
-----Original Message-----
From: John Stutz
Sent: Oct 8, 2020 2:07 PM
Subject: Re: RGS #20. Was: [HOn3] Division Point K-27 question

Thanks Earl

You are quite correct, on both counts, although one only needs to close the angle cocks to uncouple and switch cars wile the brake reservoir is charged.

On October 7, 2020 at 7:22 PM Earl Knoob <earlk489@...> wrote:

The semi-official term for releasing the air from the aux reservoir under the car is called "bleeding the car off".  It is used when a car with the brakes charged is uncoupled and the brake hoses part, setting the brakes.  In order to release the brakes without hooking the hoses back up (switching without air brakes is pretty common), you have to pull on the "bleed off rod" to release the remaining air out of the aux reservoir and brake cylinder. 

From: <> on behalf of John Stutz <john.stutz@...>
Sent: Tuesday, October 6, 2020 1:46 PM
To: <>
Subject: Re: RGS #20. Was: [HOn3] Division Point K-27 question

This use of dump is new to me.  In North America, dumping the air on a car means to release air form the car's air reservoir.  Dumping the air on a train means to release essentially all air from the train line, which immediately triggers emergency braking. 

From your description, dumping air to release the brakes, the Wolsztyn line is using a straight air brake. 

On October 5, 2020 a t 11:12 PM Mark Kasprowicz <mark@...> wrote:

A few years back I drove steam trains on the Wolsztyn line in Poland. Each of the locomotives had a brake dump operated by a wire inside the cab. It was situated by the cab side on the drivers side. It was used to release the train brake when it was slow to release.

Mark K
Oxon England


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