What does this mean in relation to train brakes?
When the air brakes are released on a car, the pressure in the cylinder that provided the braking effort has to be exhausted to the atmosphere.
This air passes through a small valve called a retainer, which has four positions. The normal is called release, which allows the exhaust to pass directly to the atmosphere. The other positions allow some of the pressure to be “retained” in the brake cylinder, which means that the brakes on the car are still on even though the control valve is in release position and the brake reservoirs are being recharged from the brake pipe. These other positions yield varying rates of exhaust of the air from the cylinder, according to the conditions to be dealt with.
The retainers have to be set up by hand, and are used on long grades to keep the brakes on the cars - and the train from running away - while the reservoirs are recharged for the next brake application.
They’re “turned up” (set to retain) before descending the mountain, and are “turned down” at the bottom, for normal operation.
They’re a great safety device - ask any mountain hogger.
Old Timer
Set by hand? Some poor guy has to walk the length of the train and do this before and after the trip down the mountain?
Yep! Hard work, on mountain grades brakeman really had a job. The main reason for using retainers is to allow the brake compressor recharge without having to reapply the brakes before it can do so.
To fully understand this concept you have to know how the Westinghouse Automatic Air Brake system operates. The most simple answer is that to release the brakes, you pump up the air, and to set the brakes, you lower the air pressure. In that way, if the train does come apart, the brakes will automatically apply.
As Old Timer stated, there are various levels of “release” available going all the way from a rather quick 10 minutes “of braking power” to absolutely no release whatsoever. This system was used prior to dynamic braking or when dynamic is not available and usually requires a caboose with a brakeperson riding in it. At the point where the extra braking power is needed, the train comes to a complete stop and the engineer puts gives a full set (23 lb reduction for frieght and 43 lbs for passenger) and the brakeperson goes forward turning up the retainers as instructed by the conductor. This is always done from the rear forward and usually is done on every other car.
When the brake person is done and back on the caboose, the engineer sends back a release, which releases the brakes on the cars with the retainers turned down and keeps the full set on the other cars (turned up). The train is then started and continues on for a set period (either time or distance, but usually a combination of both) that is short enough not to let the wheels get to hot, where the train is stopped, the retainers that had been turned up are now turned down and the other retainers are turned up. This process is repeated as often as necessary and permits wheel cooling while the train is in motion rather than waiting for 15 to 30 minutes for a standing cooling period.
With the arrival of the “Lap” position on the brake valve and the Pressure Maintaining Brake this practice was reduced greatly - in most areas it disappeared completely. The engineer was able to do the retainers job with the train air, but it was to all cars or to no cars, and rolling cooling was usually not permitted. The a
Lovely explanation Eric! The only thing I might add is first that retainers – either by hand or by various more sophisticated on-car equipment – are still used on some grades, and if they are required, somebody has to walk the train to check them. Second, while dynamics are usually used instead, when figuring the power required and braking available for a train, you are not permitted to factor in the dynamics. Either the train has enough air brakes, or she doesn’t roll. There have been several really bad accidents in the past where the dynamics failed for one reason or another, and the train got away.
Jamie – now, could you just be learning things???[:D]
On the “Good Olde Friendly” it was “TOPB” – Tons per Operative Brake, and every grade too steep to stop a car with only a hand brake had a “TOPB” assigned. It said so in the Special Instructions.
Wow…What a complicated bit of data…I’ve listened to these explainations for years and still have a muddy understanding of what it’s all about. It almost sounds like the train is stopped to manually set these “retainers” to overcome a deficiency in the brake design. Several years back and a couple in a row we stopped each Spring on the way back from Florida…at Saluda, NC at the famous NS grade and talked to people of their famous “hill”, etc…and learned that was one procedure that took place there in the town of Saluda…{the grade summit}. Before the crew would even think of starting down the grade the retainers had to be set…So it was mandatory to do this on that hill…dynamics or not. I suppose I just don’t quite understand why a brake application from the engineer couldn’t accompli***he same thing…Is there a danger of the brakes becoming party released as the train would make it’s decent of the hill and hence “turning up the retainers manually prevents this…” ? I know this “hill” would require major breaking power as it was, {is}, a 4.7% grade in general for several miles…Any thoughts…?
Good heavens yes! I’m always learning things! One of the best reasons to read these forums![:D] And you’d be surprised (well, maybe you wouldn’t…) how often I find out I’ve been wrong or misunderstood something…[:)]
It’s all related to recharge time of the brake reservoir. If the brakes are set and released several times in quick sequence, the air pressure in the braking reservoir will be drained and have no time to recharge. That would cause a total loss of braking power. Not a design flaw as much as a design limitation. One requirement for train air brakes on cars to be used in interchange is that it be operationally compatable with all previous braking systems. In theory, the oldest train air brake system will work with the newest, but may not have some of the features of the newer system, like stepped application.
A full and complete stop MUST be made to either turn retainers up or down. Depending upon your Companies Rules or the Special Instructions, you may also be required to do a “blow and go” (set and release brake test). Retainers do not correct any deficiency as such but alter the way a brake application and its release are handled by the cars so as to keep the brakes applied on some cars and not on others when the engineer has released the brakes.
The problem comes in several pieces and can get a bit complicated, so I will try to keep it very simple - and thus not quite complete![:0]
As I mentioned in a post above, it takes an increase of air pressure to release brakes, and the locomotive can only pump a specific amount of air in a given period and the brake pipe can only handle a certain specific amount of air in a given period.
That means that there will be a delay - both in releasing and setting the brakes and also in charging the air resevoirs on the each car as well as each locomotive. The resevoirs MUST be fully charged to have a proper brake application. And to charge the resevoirs, the brakes must have fully released, so there needs to be a method of keeping the brakes applied while the recha
I read a book about a lumber company. In a story from a brakeman about retainers, they used to keep the train rolling (crawling) as the retainers were released, and they worked from the front of the train to the rear when doing so.
Ok old head trick for you. Lets say your train is held waiting for something and a guy in the pool leaves before you ( for some reason this is BAD BAD BAD I think let em run around me I get to stay home longer)and you dont want that. So you take a broom handle and whack the retainers as the train is pulling by you. Retainers set up and at the first TWD that calls for them to " stop your train. sticking brakes on axle 488" you run around them waving and smiling and hoping they dont have a broom ready for you.
Eric: Understand recharging needs for each reservoirs, etc…but on a grade such as I mentioned @ 4.7% or more…I would imagine an engineer would not be charging the brake line to do any brake releasing…Wouldn’t he want those brakes to drag all the way down that excessive grade…
The book I’m reading talks about retainers and a runaway UP train on the Cima Hill in 1980. Thanks for the information.
What happens is an engineer will tend to put on just a little too much break, now you would set you brakes and adjust speed with the dynamics, back then if you put too much on, you had to release, and recharge. If you didn’t you would roll to a stop. All the brakes work, some of them just continue to apply when released.
…On the grade I’m referring too I believe we’d not see “too much” brake being used…That grade of 4.7% plus with a loaded train is excessive…I don’t think there is too much concern of rolling to a stop decending on that grade. At one time the “hill” contained 2 runaway tracks and just a few years ago when it was embargoed it still had an operational runaway escape track…!
That is exactly what retainers do. They keep the brakes applied while the air is recharged.
…One thing I didn’t hear in talking to residents of the little summit town of Saluda…When the train is stopped at the top of the “hill”…I don’t know if ALL of the cars had the retainers set…In my opinion just observing the steepness of the grade…{it’s hard to believe it’s a railroad on that grade}, one would think each car, especially if loaded would need it’s retainer…“set”…{In all the visits, I never got to witness this operation…even after waiting for up to 4 hrs…}.
Are there any other grades (since Saluda is mothballed so it is not in use today) that require the use of retainers regularly? I can only think of one grade in use today and retainers are only required if the train stops while going down the hill, then some retainers need to be set before moving. This is a rare occurance as trains don’t stop here.
I know of abandoned lines that required retainers on all downhill trains, but are there any lines that would use retainers regularly in use today???
ps; I have seen some old Southern Pacific refers or box cars that had the retainers up high with the hand brake wheel. Does this sugest that the brakeman adjusted the retainers while running across the roofs while the train was moving? Most cars had them located to reach from the ground.