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Minimum loco boiler regulator tube size?

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Minimum loco boiler regulator tube size?

Home › Forums › General Questions › Minimum loco boiler regulator tube size?

Viewing 7 posts - 1 through 7 (of 7 total)
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  • 5 January 2017 at 10:07 #24985
    Greg H
    Participant
      @gregh
      5 January 2017 at 10:07 #275850
      Greg H
      Participant
        @gregh

        Hi,

        I'm building a boiler for a 3 1/2" loco and It's limited for space inside the boiler. So I was wondering what's the smallest size tube that I could use for the regulator that would not restrict the steam supply.

        The loco is 2 cylinder with 1 1/8" bores.

        I was hoping 3/8" OD tube with 0.8 mm wall thickness would be ok. The original design was 1/2" tube, but I will struggle to fit this in.

        My design has to be to the Australian boiler code and so I have to make some changes to the stays to make it compliant which is what's reducing the internal space.

        What do people think?

        Greg

        5 January 2017 at 12:05 #275878
        duncan webster 1
        Participant
          @duncanwebster1

          Need stroke, wheel diameter and anticipated running speed to make any sensible calculations

          5 January 2017 at 12:16 #275880
          Greg H
          Participant
            @gregh

            The stroke is 1 5/8"

            Wheels 4 3/16"

            Running speed – As fast as a 3 1/2" loco would normally go. smiley

            Max boiler pressure 90psi

            Is there a formula that can be applied?

            5 January 2017 at 12:30 #275882
            julian atkins
            Participant
              @julianatkins58923

              Hi Greg,

              3/8" pipe will be perfectly ok for the regulator steam pipe.

              I am surprised 1/2" dia pipe is specified as this is most unusual for 3.5"g locos and small and medium 5"g locos.

              Cheers,

              Julian

              5 January 2017 at 13:05 #275887
              duncan webster 1
              Participant
                @duncanwebster1

                My immediate thought was that Julian is right, but some sums never go amiss

                the swept volume per rev is 105880 cu.mm. If the loco is doing 8mph at 100% cutoff, the steam speed down the proposed pipe is 23 m/sec, which is quite low (usual figure for steam pipework systems is 25 to 40 m/sec). With steam at 6.5 bara, the dynamic pressure (density*velocity^2 / 2) is 897 Pa (0.13 psi). The pressure lost going round bends etc is the dynamic pressure multiplied by the loss coefficient, which is usually less than or equal to 1, so the proposed pipe is plenty big enough. I'll bet it has a much larger area than the hole in the regulator. In reality you don't get 100% cut off and full speed, and so this sum has a lot of conservatism, a much smaller pipe would suffice, but not much advantage

                5 January 2017 at 21:24 #275954
                Greg H
                Participant
                  @gregh

                  Thanks guys and thanks Duncan for the detailed analysis.

                  I've started bashing the copper for my boiler and didn't want to find out later that I'd made a poor decision with the design.

                  Greg

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