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True North Snow Machine Mechanics

Discussion in 'Special Effects' started by Chris Chapman, Sep 12, 2008.

  1. Chris Chapman

    Chris Chapman Active Member

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    Occupation:
    Technical Director
    Location:
    Greenville, Michigan, United States
    Hey, can anyone confirm or tell me if I'm mistaken in my diagnosis of what's wrong and how the plumbing works on a Le Maitre True North Snow Machine? We were doing annual maintenance on one and are having difficulties.. which lead to some interesting engineering observations.

    I'm observing this series of connections: Intake tube with filter goes directly into "pump" on left side of unit, forward of the electronics control board. This changes into an outflow line that goes directly into the fan assembly.

    If you follow the intake tube down to the "pump" I am observing the following things with the "pump". The pump contains a spring loaded piston inside a brass and steel sleeve. This sleeve is mounted inside a electromagnet. When the "pump" is energized, the magnet activates, the piston withdraws and fluid flow begins. My question, is what is actually causing the fluid flow? The Le Maitre Tech told me I need a syphon feed going to get draw on the pump, but as far as I can tell, there is no mechanism that is actually lowering air pressure to create a draw. The Outflow tube dumps at the fan, and I assume that is on the side of the fan that airateing the fluid so the bubbles turn into foam and snow. Do these units rely on a syphon feed for the fluid? With pure water I can barely maintain a flow, and snow fluid is MUCH more viscous than water.

    Since the machines are shipped dry, how would a syphon be created in the first place with no actual pump onboard? Am I wrong and the actual pump is in the fan assembly? IF you ever got into the situation where the snow fluid ran out you'd be outta luck again and have to re-create priming the syphon. That just doesn't make sense to me.

    Le Maitre has NO drawing available for public consumption on their website concerning the internal schematics, etc.

    Ideas? I mean I'm going to have to send the machine off for repairs, but I'm wondering if I'm just totally misreading the layout of this gear.

    Thanks,

    -Chris Chapman
    TD, Greenville Performing Arts Center
     
  2. jwl868

    jwl868 Active Member

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    Location:
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    This is a guess on my part based on your description. I have no experience with the machine: The pump as you described it sounds like a solendoid-driven piston (or diaphragm) pump. This pump would also have a check valve on the inlet line that allows only flow in and another check valve on the outlet that only allows flow out. (These check valves are probably spring-loaded.) When the piston withdraws, a vacuum is created, fluid can only flow into the chamber through the inlet line and the outlet side check valve prevents flow from the discharge line. When the piston reaches the top of its range, it reverses direction. As the piston reverses and pushes fluid out of the chamber, the fluid flows through the outlet check valve, and the inlet check valve prevents flow that way. Then the cycle starts again.

    The first several strokes should "prime" the system, especially if the tank is full. A pump of this type draws a vacuum.

    Possible problems:
    - the inlet filter is clogged.
    - the inlet tubing is kinked.
    - the inlet tubing has a hole.
    - the inlet tubing/pump inlet joint is leaking.
    - the piston seal is worn.
    - a check valve seal is worn.
    - a check valve spring is broken.
    - debris has jammed a check valve so that it doesn't seal closed.
    - the piston/solenoid is not cycling (electronics problem).


    (My money would be on a check valve seal problem.)


    Joe
     
  3. Chris Chapman

    Chris Chapman Active Member

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    Occupation:
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    Joe,

    That does indeed sound like the mechanism in question. Thanks for that little clarification. I have a nutty feeling that the spring loaded portion of the piston hasn't been reassembled properly.

    -Chris
     

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