What type of hopper it this?

Generally speaking, the car is a pressure differential (also referred to as PD) type hopper.  Specifically, it's a Thrall PD5000.  The PD5000's were originally manufactured by North American Car Company (NACC), then by Thrall, and then on to Trinity.  There is also a PD3000 version, which is shorter with less volume, and with only 3 outlets.  Trinity now manufactures a different version of pressure differential car, but there are plenty of the old NACC style cars still on the rails.  Similar cars are/were made by ACF and Greenbrier.

The cars are normally pressurized during unloading, at around 15psi.  I'm not sure if there is also typically vacuum applied to the outlet pipe.  My instinct is that pneumatic conveyance systems are typically either pressurized to push material, or have a negative pressure to pull material, but I've never known them to be both at the same time.  But I don't know that for certain, I'm pretty familiar with pressurized systems for moving cement and sand, not so familiar with vacuum systems.  In any event, the goal is to fluidize fine or powdery dry goods, or pills, or cereal flakes, etc,  so that they flow like a liquid.  There are quite a few things that can be conveyed in this manner.  The car in your photo could be hauling flour, I'm not sure what else they use them for.  The smaller 3-bay versions haul cement, sand, roofing granules, and a few other dense materials.

There is an O scale version of the car in your photos, done by Overland Models many years ago.  They also did a PD3000 if I recall correctly.  I don't think anybody else has done one, and I don't think anybody has offered any of the versions manufactured by ACF or Greenbrier.  Atlas does make the newer Trinity 3-bay and 5-bay hoppers in N and HO scales, based on the tooling they acquired from BLMA.  I would love to have some modern Trinity 3-bay cars for cement service.

Jim

Wow... Thank you Jim for the history lesson.  I appreciate it very much.

Vr

Ron

No Problem.

If you wanted to take a shot at modeling a PD car, you might consider the ACF version.  You could start with a Weaver 4-bay hopper with round roof hatches without spending too much on something you are going to cut up.  The volume is a bit different for the Weaver car than for the prototype, but it's close enough.  Alternatively, you could start with the Lionel aluminum 4-bay, but those are harder to come by and generally more expensive than the Weaver cars.

You can find lots of information about the under car piping and gates from the Salco website.  They offer replacement aftermarket parts for various hoppers and tank cars, and they have information specifically for the ACF cars.  They list parts, and include dimensioned cad files for most of them including valves and other fittings.  It's a great resource for some very specific information.

One thing to note about the ACF Centerflow PD cars, they do not have the typical angled horizontal stiffener at the top of the car side.  You would need to remove that if you wanted to get more accurate.  There are plenty of photos of the ACF cars here, generally with SHPX reporting marks, in the 43000 car number range.

Jim

A bit of correction to my post above.  The CMHX 97065 car is the original NACC design, and would appear to be built by NACC as opposed to Thrall or Trinity.  CMHX 97020 is of the later design car introduced by Thrall in the late 90's, now offered by Trinity.  The jacking pads and slope sheet designs are the clues.

Jim