Freight Car Friday – Pressurized Covered Hoppers

11 04 2014

Covered hoppers can be used for a great variety of loads. Some of these loads can be a little stubborn when it’s time to be unloaded. Pressure differential, or more commonly referred to as simply “pressurized” covered hoppers are one of the more common modifications to facilitate unloading these commodities.

PD 3000

BCAX 10241, a NACC PD-3000 model, is on the smaller scale for pressurized covered hoppers. These can be found hauling cement, lime, talk, caustic soda and similar materials.

Pressurized covered hoppers come in all shapes and sizes. Like other conventional cars, their size and capacity is tailored to the density of the load. This maximizes payload while staying within the weight limits of the trucks. The size and number of roof hatches, angle of the slope sheets and sides of the car and size of the discharge outlets can also vary according to the specific needs of the shipper. And of course there are the different looks offered by competing car builders as well.

The one easy spotting feature for a pressurized covered hopper is the extra piping around the hopper bays used to pressurize the car and remove the contents.

DMIX 5100

DMIX 5100 is a larger, 5100 cu ft. capacity car. These commonly haul everything from flour to fly ash.

These cars are not pressurized for the entire trip. At the receiver’s siding, the cars are attached to a stationary air supply. Air flows into the car, often through outlets beneath the load, pressurizing to about 15 psi.

As the air passes through the lading, it loosens and dries the load, like the Airslide cars discussed in an earlier blog. The added pressure inside the carbody then helps push the contents out through the discharge pipes at the bottom of the hoppers and into storage silos or even waiting trucks.


The ACF Pressuraide car was the pressurized version of their popular Centerflow design. Most of the company’s leased cars could be easily identified by the blue “wings.” This car is leased to Interstate Brands.

Because the load can be pumped out through outlets on the sides of the hopper bays, no pit or conveyer system is needed. Unloading facilities can be minimal. Even an empty siding or team track can be used if the load is transferred into a truck for delivery to an offline customer. (These are easy “industries” to add to your model railroad when you’re short on space.)

Besides these offline customers, pressurized covered hoppers can be seen serving a lot of industries. Smaller cars (around 3000 cu ft. capacity) are most commonly associated with cement but there are other similar mineral loads as well. Mid range cars (4600-5100 cu ft.) haul flour, corn starch, kaolin and fly ash. The largest pressurized cars are around 5600 cu ft capacity and typically haul certain types of plastics – most commonly PVC and polystyrene – as well as cars lined for food-grade service or unlined for mineral service.

Freight Car Friday – Airslide Covered Hoppers

7 02 2014

In the wide world of covered hoppers there are many variations and patented innovations which make cars better suited for specific commodities. These also make train watching a lot more interesting for all of us! General American’s “Airslide®” cars are certainly near the top of the list of these important designs.


The low morning sun highlights the hoppers and underframe details of a GACX Airslide.

The Airslide was first patented in 1953, the same year Pullman Standard introduced their PS-2. What made the car unique was a set of fabric membranes in the hopper bays. Made of tightly woven cotton and treated with silicone, the Airslide® membranes were moisture-proof but allowed air to pass through. Compressed air was supplied at the unloading site and passed through the membrane up into the load. This aerated the load, allowing it to flow easily through the hoppers.

An article in Railway Age in 1956 touted the cars’ loading speed,

“In actual test, one major company found that one man unloaded 101,100 lb of material from an “Airslide” car in 2 hours, 18 minutes. A standard hopper car, meanwhile, with 70,000 lb load and two men working, required 5 hours, 15 minutes to unload.

“General American reports that, at least up to this time, it hasn’t found a conveying system with capacity to unload the car at its maximum potential speed.”

The conventional covered hopper was not the Airslide’s only competition. Many shippers were still using bagged loads in boxcars for these types of loads. Many shippers found a use for the cars. Flour, sugar, and other soft, dry granulated materials are common loads.

hopper details

The horizontal pipe supplies compressed air to the membrane inside the car. The bracket on the car side above is for attaching a mechanical shaker to further persuade the load.

Two types of hoppers were available. Some had a simple gravity outlet which dumped the contents straight down. They could be unloaded into a pit between the rails or onto a conveyor or auger placed under the car. A pneumatic unloading port was also available on the hopper. A hose could be attached to this for pneumatic unloading directly from the car.

By using these devices, the Airslide didn’t require as steep a slope in the hoppers themselves as in conventional covered hoppers of the day. This allowed more space for increased capacity without increasing the length of the car. Placing all of the structural components, except the center sill, on the exterior sides and roof also made the interior easy to clean.

General American built its first demonstrator in 1953 and production began in 1954. Many of the first cars were built for their own lease fleet. Many of these in turn were put on long-term lease to private shippers and railroads. These cars would have shippers / railroad logos and graphics but GACX reporting marks and numbers. Many of the railroads that initially leased the cars ended up buying them outright.

single bay

VFLX 10026 is an early 2600 cu ft car. The roof has been modified with a new centered hatch. This is part of a 2-unit car. The cut levers have been removed between them to make a semi-permanent car.

Both 2600 and 5300 cu ft. cars were offered. The 2600 cu ft (also commonly called the “single-bay” or “40 ft” Airslide) was the most popular for the first decade. Approximately 5000 cars of this size were built up until 1969. The cars featured a single hopper on each side of the center sill. From the side sill up, the cars had a more boxcar-like look than other covered hoppers of the day. The ends featured open areas inside the safety rails and ladders which provided access to the loading hatches on the roof. Air brake equipment was located in this space on one end of the car.


BN 410322 gives a good view of the roof details of an Airslide. The roof panels next to the hatches are coated in an anti-slip material for safety.

In the 1960s and 70s, more shippers began opting for the 5300 cu.ft. version of the car. These featured a pair of discharge outlets on each side and were 50′ long.

As the demand for the larger cars made the earlier 40′ cars surplus, many of these were semi-permanently coupled with drawbars into paired single-bay cars. Some of the most recent conversions have been even more simple – only the coupler cut levers have been removed to make the semi-permanent connection.

Between the paired 40′ and more common 50′ cars, there are still hundreds of Airslides on the rails today. Some are owned by railroads, many are privately owned or are part of GATX’s own lease fleet.

New Product Spotlight – CP Rail Grain Train Set

30 12 2013

Now the excitement of those long and colorful unit trains of Canadian grain can be brought to layouts of any size with this new Ready-to-Run set. Based on some of the many popular paint schemes of the Canadian cylindrical covered hoppers and powered by a locomotive in the attractive “Dual Flags” scheme of CP Rail, this set is ready for the wheat rush.


6-30210 CP Rail Grain Train Set is ready for the harvest.

Beginning in 1972, the Canadian government began financing the construction of several thousand covered hoppers for agricultural service. These would finally bring an end to the days of loading grain in 4o foot boxcars. Most of the cars were financed by the national government and wore a variety of colorful schemes. They were leased to Canadian Pacific and Canadian National with CPWX or CNWX reporting marks on the cars.


The colorful cars can still be seen today all over North America.

Several provincial governments also supplied  cars to the pool. The bright blue Alberta cars featured unique names of towns and counties. Saskatchewan has recently added new cars in one of the most colorful schemes yet. In addition to all of these, the major Canadian railroads ordered their own cars. All together, these cars operated out of a general pool so they would be available wherever and whenever needed.

Much of the grain carried in these cars was destined for ports and shipment overseas. As CP and CN expanded their networks in the 1990s with the purchase of some strategic American railroads the sight of the Canadian covered hoppers and locomotives south of the border became even more common.

Now you can handle this lucrative traffic on your railroad with the new CP Rail Grain Train. This complete set includes a CW-80 transformer, 60″ x 40″ oval of FasTrack, U36B locomotive, three covered hoppers and a caboose. The locomotive features:

  • Transformer Controlled Forward / Neutral / Reverse
  • RailSounds RTR including diesel engine revving, horn, bell and operator-activated crew dialog
  • Dual Motors
  • Traction Tires
  • Metal Frame
  • Operating Headlight
  • Illuminated Cab Interior
  • Dual Operating Couplers
  • Engineer and conductor figures

The covered hoppers feature operating couplers, and sprung die-cast metal trucks. The caboose features a metal frame, ladders, smokestack and trucks plus interior illumination. All of the cars and locomotive will negotiate an O-27 curve. See your dealer or to order your set today. Retail price for the set is $389.99.

Freight Car Friday – Carbon Black Cars

29 11 2013

It is “Black Friday” after all! These distinctive covered hoppers have roamed the rails since the 1930s. The typically black covered hoppers are anything but boring. And while they can be found all across North America, with their low numbers and specific commodities if you’re not along a route they normally frequent they would be easy to miss altogether.

What Is Carbon Black?

CCX 441

CCX 441 is part of a large block of cars headed to Columbian Carbon’s Hickock, KS plant. This is an ACF-built car – the Center Flow design is apparent.

Generally speaking, carbon black is a variety of amorphous carbon. It can be made in several different ways. Most is made by the incomplete combustion of hydrocarbons in a furnace (furnace black). It can also be produced through thermal cracking of natural gas (thermal black) or incomplete combustion of acetylene (acetylene black).

Carbon blacks are used in a variety of products. The majority are used in making tires. When added to rubber, carbon black increases strength and resistance to abrasion. It is also used for inks and paints, wire insulation and other rubber products. Acetylene black is electrically conductive and used in dry cells and explosives.

Produced at about 20 different plants across the United States and Canada by a handful of companies, the product tends to move in small shipments (one or two carloads) to specific customers over routine routes. If you happen to be near, or along the route to one of these producers or consumers then you’ll see these cars regularly. Otherwise, you’ll have to look hard to find one.

Carbon Black Cars

TCMX 96125

A low angle view of TCMX 96125 gives a clear view of the distinctive discharge outlets. The sampling spigots can also be seen.

What differenciates a carbon black car from a “standard” covered hopper? Like most commodities, covered hoppers are customized to meet the needs of the carbon black industry. Aside from the obvious black color chosen for most paint schemes (a concession to the weathering effects) carbon black cars usually have several other things in common:

  • Cars typically have three relatively small 16″ butterfly outlets on the bottom of the car for unloading.
  • Roof hatches are also typically small, 8″ or 16″ and found in greater numbers than typical larger hatches
  • Sampling spigots on the car sides
CCX 647

Showing just how different these cars can look, here’s another Columbian car from the same cut. the full side sheets on these Thrall cars make them look more like a boxcar than covered hopper.

Cars have been built to a variety of capacities and designs but 77 ton capy. cars are most common. ACF, Darby Car, GATX, Magor, National Steel Car, Pressed Steel, Procor, Pullman-Standard and Thrall have each built cars. The cars were generally built in small quantities and there were many subtle differences between runs and not-so-subtle differences between builders.

While these cars may not be frequent sights on the rails, once you’re aware of them it is fun to start taking pictures and comparing notes. You can watch trains for years and not see two exactly the same! Keep your eyes open as you go train watching, you never know when one of these black snowflakes will show up.