air brakes on trains

[BaltACD]

loco6625

So am I correct that the main reservoir on each car has 2 compartments divided equile, one side for service application only, and one side for emergency, so when emergency is applied, both reservoirs dump through the triple valve and into the brake cylinders for the higher brake shoe pressure. So when the triple valve pull rod is pulled in hump or flat yard switching operations, does it dump both sides of the air reservoir, or maybe only the emergency side, so when the air hoses uncouple, there is still air left in the service side? If so, would the air left in the service side help when the train is made up and the air test time would be shortened?

When cars are bled off for flat switching or humping - there is no air left in either air resevoir.

[xrrman]

Deggesty

I appreciate the willingness of those in actual railroad service to share their knowledge with those who have an interest in railroading. After more than sixty years of absorbing such knowledge, I still know that I have much to learn.

However, in the discussion of engine brakes, I feel that one important factor has not been stressed: the independent, or engine braking, system does not have the same kind of valve that is present on every car in the consist, but depends on a direct, or straight, application of air from the engine's reservoir. There is no separate air reservoir for the engine's braking system, so when the air leaks out of the engine's braking system and the air pump does not kick in, there is no air to keep the engine brakes applied.

BigJim, a thought occurred to me; am I right that the brakes on a steam engine's tender were also set by straight air?  

And, I recall the account of the rookie fireman who, when told, "that pipe is for the straight air," wondered how straight air could be put into such a crooked pipe. 

Actually the engine brake is quite similar to the car brake.  When an automatic brake application is made the engine brakes react and apply just like a car brake.  Since this is usually undesirable the engineer must "bail off" or actuate the independent brake lever to release the brakes on the locomotives.  The engine brakes will remain released until either a further automatic brake or an independant brake application is made.

[Deggesty]

Quoting xrrman: "Actually the engine brake is quite similar to the car brake.  When an automatic brake application is made the engine brakes react and apply just like a car brake.  Since this is usually undesirable the engineer must "bail off" or actuate the independent brake lever to release the brakes on the locomotives.  The engine brakes will remain released until either a further automatic brake or an independant brake application is made." 

True--but the engine brake is still straight air. That the engine brake is set when the train brake is set and is bailed off at the engineer's discretion has long been a feature on locomotives, dating from steam engine days.

[BigJim]

loco6625

So am I correct that the main reservoir on each car has 2 compartments divided equile, one side for service application only, and one side for emergency,

The short answer is - No, you are not correct.

The reservoir on the car is divided into two sections, however, there is a cone placed inside that makes the emergency side much larger than the service side.
 

so when emergency is applied, both reservoirs dump through the triple valve and into the brake cylinders for the higher brake shoe pressure.

What you have to realize is that an emergency brake application is not a "wham-bam-thank you- maam" operation. The control valve controls which side of the reservoir opens and at what time in order to get the higher braking effort.

The best way that I have found to visualize what happens comes from WABCO and involves barrels of water. Draw three tall rectangles (barrels) side by side. Color the first two blue to represent the Emergency and the Service side of the air reservoir fully filled TO THE SAME LEVEL. This level represents the feed valve setting or brakepipe pressure that fills the reservoirs. Leave the third one blank to represent the brake cylinder.

On the first two, draw something on the bottom to represent a valve that can be opened. Now, from each valve, draw a line to represent a pipe and connect it to the barrel representing the brake cylinder.

Now, fully open the valve on the Service barrel. The water, representing the air, will drain into the empty brake cylinder barrel until both levels equalize. Do you see and understand this? No more pressure can be put into the brake cylinder from the service side of the reservoir. The pressures have equalized.

Now, fully open the valve on the Emergency barrel. Note that since it is fully filled, some of the water will drain into the brake cylinder barrel until they too equalize at the same level. This level is higher than the level before and represents the additional brake pressure attained in an emergency application. Savvy?

So when the triple valve pull rod is pulled in hump or flat yard switching operations, does it dump both sides of the air reservoir, or maybe only the emergency side,

In switching operations, only the brake cylinder needs to be exhausted. When the bleed rod (depending on the type) is given a short pull, for the most part it only releases the air in the brake cylinder. If the entire reservoir needs to be exhausted, then you need to push/pull & hold the bleed rod until all of the air is exhausted.

so when the air hoses uncouple, there is still air left in the service side?

When a train line separates, air remains in both reservoirs because not all of the air in athe reservoirs is needed to apply the brakes.

If so, would the air left in the service side help when the train is made up and the air test time would be shortened?

When the engineer releases the brakes after an application, the control valve will sense the rise in pressure and use a little bit of the air from the emergency reservoir to help recharge the trainline.