24″ HO pipe fittings

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    MicroTraxx
    Keymaster

    I was in a Hangout and talking to Curtis Hunt about HO scale pipe fittings. He asked me about HO scale 24″ fittings.

    At the end we need to find something that we can use for the pipe and create fittings to fit. What we use for the pipe needs to be available to everyone. Evergreen styrene is readily available so let’s go with that. There are a few of things to bear in mind (following taken from Nominal Pipe Size).

    • Nominal Pipe Size (NPS) is a North American set of standard sizes for pipes used for high or low pressures and temperatures
    • Nominal Pipe Size: Pipe can be high or low pressure and everything in between. The “Nominal” refers to a pipe in non-specific terms – in that the hole in the pipe will vary as the wall thickness varies with the criterion being the outside dia.
    • For NPS ⅛ to 12, the NPS and OD values are different. For example, the OD of an NPS 12 pipe is actually 12.75 inches.
    • For NPS 14 and up, the NPS and OD values are equal. In other words, an NPS 14 pipe is actually 14 inches OD
    • The reason for the discrepancy for NPS ⅛ to 12 inches is that these NPS values were originally set to give the same inside diameter (ID) based on wall thicknesses standard at the time. However, as the set of available wall thicknesses evolved, the ID changed and NPS became only indirectly related to ID and OD.

    For modeling understand that we are not going to make exact pipe dia in scale – at least not using off-the-shelf products like Evergreen tubing. For me .. “close” is “good nuff”.

    Curtis wanted 24″ pipe .. or at least .. ‘near so’. Let’s look at what Evergreen tubing is available near a HO 24″ dia pipe.

    • 0.276″ – 24″ HO
    • #229 – O.D. 9/32″/0.281″/7,1 mm – 24.48″ HO
    • #229 – I.D. – 0.225″/5,7 mm

    That means that Evergreen #229 tubing is only .005″ larger dia than a scale 24″ HO pipe. That’s more than “Good nuff” for me. Heck that’s only 7/16″ full size!

    Pipe Flanges: One thing to consider is the pipe flange dia, thickness and number of bolts. This changes depending on the class of pipe. Here’s a look at pipe flange dimensions for 24″ pipe.

    • Class 150 – 32″ dia – 20 1-1/4″ bolts (1-7/8″ across flats and 2.165″ across corners, .876″ height) on a 29-1/2″ bolt circle
    • Class 300 – 36″ dia – 24 1-1/2″ bolts on a 32″ bolt circle
    • Class 400 – 36″ dia – 24 1-3/4″ bolts on a 32″ bolt circle
    • Class 600 – 37″ dia – 24 1-7/8″ bolts on a 33″ bolt circle
    • Class 900 – 41″ dia – 20 2-1/2″ bolts on a 35-1/2″ bolt circle
    • Class 1600 – 46″ dia – 16 3-1/2″ bolts on a 39″ bolt circle
    • Flange thickness 2.75″

    I put that in just for “the fun of it”. It looks like that for most purposes the Class 150 is used and we can go with that for our design.

    In HO then we have the following dimensions needed to start designing ..

    • 0.367″/9.33mm dia
    • 20ea bolts – 0.025″/0.63mm across corners – 0.010″/0.25mm height
    • 0.339/8.6mm bolt circle
    • 0.032″/0.8mm flange thickness”/
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