air tanks

[BigJim]

Boy, did this thread get confusing real fast!

The compressors would pump air into the "Main" reservoir on the engine in the 130psi - 140 psi range. A governor would cycle the air pumps to maintain the main reservoir pressure. 
From there the air would go to the brake stand in the cab.
The engineer would then adjust the "Feed Valve" to the desired pressure. Since we are talking steam era here, this would probably be 60psi for yard service, 75psi for freight service and 90-110psi for passenger service (These figures could vary from road to road depending on the roads rules).
The air from the feed valve would supply then feed the trainline with the selected pressure. The "Auxiliary & Emergency Reservoirs" on the cars would then be charged from the trainline to this same pressure.

Through the years trainline pressures have increased in increments to where, now, 90psi is a standard pressure for freight service.

[efftenxrfe]

Tnx....for the "better than mine."

Thru high school I rode bunches of LIRR MU trains and the sound of the air pumps on the MP54s rattles around in me still, but I never was curious about the brake system. Thank you for the enlightenment.

"repeater cars." 

They are in demand now; so are buggy whips, but SP had a few. Cat diesel, big reservoir fed by air pumps I never saw identification or characteristicts for.

The air was available to a device which would feed air from the reservoir to the rear of the train at the same pressure that the front of the train fed to it. Thus, the air that would be lost due to frigid...f' ing cold...behind the repeater was resupplied. So there were effectively two trains. 

Also, this device responded to brake pipe pressure reductions, which caused brake application, by comparing the rear end Br Pipe Pressure with the head end and reducing the rear pressure on the rear end of the train.

An aside....Eye to Eye an Alaska Rail' engr told me there were many trips they'd leave Healey with coal for points north when they couldn't get  air to the caboose, they relied on the cold journal oil and grease for braking power. They said  they flamed brake hoses between frt cars with fusees to make them bendable.

Consider repeaters and DPU's or Locotrol: they make the brake response to an engr's request for retardation briefer than response linearly from the head-end to the rear-end. And also the brake release is quicker.

I wish it were there when I hired out.

 

[rcdrye]

Your explanation is better than mine, which is based on MU car systems.  On a train with only one compressor the car reservoir pressure is set from the train line, which requires the main reservoir pressure on the locomotive to be a bit higher, since that's where the train line air comes from.

On rapid tranit/interurban train air systems, there isn't much difference between the main reservoir pressure and the train line, since every car maintains main its own main reservoir.

Canadian railroads used (and may still use) "repeater" cars to boost train line pressure on long, cold trains.

[efftenxrfe]

What we have is a failure to.....

Air Tanks....locomotives....steam locomotives.....

The three or four responses read at 1615 PDT, are correct for most fully charged frt and psgr cars reservoirs (air brake lingo for "air tanks").

Locomotives: devices governed the production of compressed air which was stored firstly and primarily in main reservoirs which stored and dried the the atmosphere pushed in them

Rail car brake systems (electronic control is on another planet) classically were controlled by changes in the brake pipe pressure, thus slow or rapid changes in the brake pipe pressure were the buggy-whip.

All this to say that to rapidly increase the brake pipe pressure to effect a brake release, while  maintaing a reserve for ancillary use, like the sanders,bell ringer..., the compressers were governed to supply air at, generally, 25- to 35 psi above the br pipe pressure.

On SP's Coast Division when I hired-out in 1960 frt br pipe pressure and psgr pressure respectively were 90 and 110 psi. The compresser governers were set to start pumping when the main reservoir pressure was bled down to 130 psi and stopped pumping at 140 psi.

In the steam era, 70 psi br pipe pressdure was more  common, and also were the heaviest cars grossing-out at 90 tons or so. Today the same compressed air automatic brake (AB) and its developed refinements slow 143 ton cars.

[rcdrye]

As far as I know even intermodals get the standard freight 90, with the possible exception of C&NW's Falcons in the 1980s.  Amtrak's Auto Train - a "mixed train" of sorts, gets 90.  The use of 110 on passenger trains was far from universal - I'm sure a lot of carriers didn't bother.

[daveklepper]

and today's intermodals, 90 or 110?

[rcdrye]

90 for freight, 110 for passenger.  Regulator on the compressor, which shut them off when pressure was reached.  Same for diesels.

[train18393]

How many pounds of air was typical for a steam engine, and was the regulation accomplished by shutting of the air pump(s) or was there some sort of regulator? Just curious.

Paul