I was just reading a article about the DM&IR and it’s locomotive fleet, which is being changed by CN. In the story it mentions that only locomotives equipped with “straight air” can lead trains down Proctor Hill to the ore docks. It also says that the ore cars use an Orinico straight air system and that some of the locomotives coming on to the property are being set up with this type of air system. Exactly what is “straight air”? Is it used for braking or to operate something on the ore cars?
The DM&IR trains have normal air brake systems, with the ‘straight’ air on the retainers. There are two sets of hoses between the ore cars. The system allows the engineer to set the retainers without stopping the train and having to have the trainmen walk the train ‘turning up’ the retainers. With the retainers set to hold air pressure on the brake piston, the engineer can do a ‘release’ if needed and charge up the train line as the train drops down Proctor Hill.
If you get a chance; Go up to Duluth and watch the white stream of brake shoe smoke from an ore train as it drops down the hill, and at the end of the ore dock is the Duluth harbor!
…Is it the weight of the loaded ore cars that is promoting such system and action…? Believe ore is heavier than say…coal. But what is the grade down said hill…?
Yes the loads ( any loads actually) woul produce the shoe smoke when you have an application on them and going down a good hill.Retainers are on every car its just DM&IR has a neat system to set up retainers without stopping ( I like that idea )On a normal car you have a three position or even four position retainer.One seting is direct exhust allowing air from the cylinder to exhaust when you release. Another is one that retains 10 lbs so you can kick off the automatic and still have 10 lbs in the cylinder while charging the system.The third setting is for 20 lbs to be retained. That 4th setting one we never use on BN so we never really went over it so some one else will have to tell you about that one.
I wouldnt want to ride it out into the harbor, seeings locomotives float like lead ducks and I am NOT going down with that ship lol.
…I’m not totally clear about the job “retainers” do in the braking system…I believe it is a possitive way of “setting” the brakes on each car so that if anything happens to the “train air system”, you still have the brakes applied as you applied them at the top of the grade…Is that somewhat the function. Not that it gives you “more” capacity of braking, just that it gives you really positive “control” that they will stay applied as you {the engineer}, set them at the beginning of the grade…Anyway close…?
Straight air for set-up and control of retainers is feasible where you have a captive car fleet, which is certainly the situation with DMIR’s ore jennies. I believe that Erie Mining Co. and Reserve Mining Co. had similar systems for their operations.
To answer Modelcar. Yes you have it pretty close. With the retainer set, the car’s brake cylinder pressure will be maintained at either 10psi or 20psi, for the “LP” or “HP” position of the retainer valve. As stated before this allows the engineer to recharge the brake pipe/ auxiliary reservoirs (local air supply on each car which is the main source of air for the service brake application) while retaining the brake application already in effect. On older rail cars there was an “SD” position also, this retained brake cylinder pressure for aprox 86 seconds, before it fully released.
There is one thing that can go wrong using retainers. If the seal between the piston and brake cylinder body is leaking, the brakes will leak off on that car.
Route_Rock’s explanation covers a lot of it. A visit to Al Krugs air brake explanation would be useful, too.
It’s necessary to fully release the train brakes to fully recharge the brake reservoirs on the individual cars. Without retainers, that would make the cars free-wheeling, of course, possibly leading to a runaway. The only way to lessen the braking on a train is to fully release the brakes, unlike your car, where you can modulate brake pressure with no loss of braking efficiency.
The retainers maintain pressure in the brake cylinders even though the trainline pressure has been restored to its normal released pressure (usually 90 lbs for freight). That allows the reservoirs to recharge to full pressure. Having less than full pressure available in the reservoirs means less available braking.
It’s possible for an engineer, through repeated sets and releases of his brakes, to run the reservoirs out of usable air (and braking) if he doesn’t allow enough time between applications and releases for the cars to recharge. A full charge from zero can take 10-15 minutes (or more) for a long train - that’s a long time if your train is running away from you.
…I understand the examples you relate Larry…I know, down at Saluda, N C at the top of the “hill” there on the NS RR they would stop and “set” retainers when that route was still being used. Due to extreme steepness of the grade, all precautions were mandatory.