The Pressure
Differential, or “PD” covered hopper was designed as a competitor
to the General American Transportation Airslide hopper
in the early 1970s to transport light, powdered materials. Unlike
the Airslide, which forced pressurized air up through a fabric liner
to help fluidize the cargo, the PS series of hoppers applied both
a positive pressure of about 15 lbs. psi above the outlets as well
as a
vacuum at the outlet to help draw the cargo from the car. This design
was well suited to products with very small particle size, such
as
talc, clay, plaster, and cement which would readily foul the fabric
liner in an Airslide design. In addition, since the upper hatches
did not
need to be opened during unloading, the PD hopper was also ideal
for transporting goods where contamination by outside air, dirt,
or
moisture could affect the load.
The Atlas 5-bay PD5000 hopper is based on the original North American
Car Company (NACC) design for a 5150 cu ft PD covered hop-
per, which was later manufactured as a 5125 cu ft model by Trinity
Industries. These cars were mostly provided as lease cars, and as
such, carried many colorful schemes and product logos during their
lifetimes, however several major railroads such as Norfolk Southern
purchased fleets as well. |
