The Smell of Molten Projects in the Morning

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The New Hotness

  • Monthly Science: Motel Water Pressure vs. Height

    Being a sucker for infrastructure and numbers, the fire sprinkler system pressure gauges in the motel stairwell proved irresistible.

    The first floor gauge shows a nice round 100 psi:

    Hotel water pressure - floor 1
    Hotel water pressure – floor 1

    Up on the second floor, it’s 90 psi:

    Hotel water pressure - floor 2
    Hotel water pressure – floor 2

    With a different brand of gauge, it’s also 90 psi on the third floor:

    Hotel water pressure - floor 3
    Hotel water pressure – floor 3

    Maybe 85 psi on the fourth:

    Hotel water pressure - floor 4
    Hotel water pressure – floor 4

    Squinting at the parallax, call it 80 psi on the fifth:

    Hotel water pressure - floor 5
    Hotel water pressure – floor 5

    At the top of the vertical pipe on the fifth, on the other side of a valve, we return to the original valve company at 78 psi:

    Hotel water pressure - floor 5 - top
    Hotel water pressure – floor 5 – top

    Water weighs just over 62 lb/ft³ at room temperature, which works out to 0.43 lb/in² per vertical foot. Not having packed my laser distance widget, I’ll guesstimate 12 feet and 5 psi per floor.

    A quick graph with an eyeballometric straight-line fit:

    Motel sprinkler water pressures
    Motel sprinkler water pressures

    Call it 0.42 psi/ft, which is pretty close to the right answer.