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Pressurized Discharge Cars/ Pressurized Unloading in 1955

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  • Member since
    September 2020
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Pressurized Discharge Cars/ Pressurized Unloading in 1955
Posted by JDawg on Thursday, September 10, 2020 6:53 PM

Hi! I am modeling the Great Northern in Northern Minnesota. I am working on a section of my layout that features the Blandin Paper Mill (BPM for short) in Grand Rapids. I am having some(ok, a lot) of difficulty in finding prototype background on pressuized discharge cars, specifically those that haul clay powder used for paper making. Anyway enough background, here's the problem. I have eyewitness testimony from a former employee that this type of car was used while he worked at BPM. It seems that the general consensus was that the PD covered hopper was introduced around 1965. Yet, my witness saw this type of unloading style (PD) being used almost 10 years earlier. My witness is extremely reliable so I know he's not mistaken. The clay was definatly brought in a powder form, not a slurry. When I showed my witness photos of PD cars he immediately recognized them, while excitedly yanking the Ipad from my hands. Bottom line, I want to know about the use of pressurized discharge type cars in the years around 1955. Please don't tell me this unloading method wasn't used then, I have my dates right! Thanks for your Help!

Tags: help

JJF


Prototypically modeling the Great Northern in Minnesota with just a hint of freelancing. Smile, Wink & Grin

  • Member since
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Posted by Overmod on Friday, September 11, 2020 2:40 PM

Part of the answer to this involves what your witness recognizes as the process being used.

PD as developed (IIRC by Trinity in the 1990s) is a combination of actions: the air provides the fluidization of the particles in the hopper (as in the earlier Airslide hoppers) as well as overpressure for flow, both at around 1atm gauge (and using positive-displacement blowing for the effective air compression).  Merely using air to flow a bulk load is not the same thing -- a key thing to observe would be whether the hatches on top of the car were open or not.  I would also have to wonder if mechanical vibration of some kind was applied to the hopper to aid effective flow rather than introducing air through internal pads. 

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Posted by JDawg on Friday, September 11, 2020 6:59 PM

Well, I asked him and he said that the hatches were always closed. He said that sometimes a seal would break and the escaping clay powder would actually eat at the metal, abrasion at work! Anyway, air was introduced at a slanted T-pipe piece near the bottom of the car. The powder would then be sucked from the car with the air added after the clay made its hasty exit. The car itself was airight. A mechanical vibrator was also used, as you suggested. I forgot to mention it in my initial post. It made an awful racket and the hopper crew used hearing protection. The clay was stored in a "cyclone" type silo. Maybe this info will help. Does this mean that a PD car was not used, maybe just a modified hopper?

JJF


Prototypically modeling the Great Northern in Minnesota with just a hint of freelancing. Smile, Wink & Grin

  • Member since
    October 2008
  • From: Canada
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Posted by cv_acr on Friday, September 18, 2020 1:39 PM

You just said "sucked out"...

Could it have been a pneumatic discharge car?

Very different distinctions between pressure-differential discharge (air pressure to move and blow out contents), airslides, and pneumatic discharge cars (vaccum unloading - like modern plastic pellet cars).

  • Member since
    September 2020
  • 7 posts
Posted by JDawg on Friday, September 18, 2020 8:04 PM

It's possible. A vibrator was used to help the clay settle. Was this type of pneumatic unloading used in the mid to late 1950's?

JJF


Prototypically modeling the Great Northern in Minnesota with just a hint of freelancing. Smile, Wink & Grin

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