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pressure relief for paint can load?

Discussion in 'Amateur Radio Amplifiers' started by W1BR, Feb 2, 2018.

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  1. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Lots of consumer products have plastic molded pressure relief valves. I have frying pan covers with those (they're inserted into glass).

    "Somebody" must make them, and I'll bet they cost five cents or less.

    I didn't do any research on this, but if you do, you may find the source who makes those.

    Otherwise, any kind of hole in the top should work as long as you never tip the can.:p
     
  2. W1BR

    W1BR Ham Member QRZ Page

    I'm sure something is out there.... even those plastic bellows used on cheap hand pumps might be adaptable. Compressed normal, allow to expand with heat expansion pressure.
     
  3. KP4SX

    KP4SX XML Subscriber QRZ Page

    Hi Pete,
    Crazy idea but you can buy replacement pressure relief valves for a pressure cooker pot commonly and inexpensively. Maybe that could work?
     
  4. W1BR

    W1BR Ham Member QRZ Page

    The weighted pressure fixtures that shake, rattle and roll? Too much vapor leakage.
     
  5. KF5FEI

    KF5FEI Ham Member QRZ Page

    I have a newer (80's) Heathkit dummy load, and it just had a fiber washer loosely attached to the top of lid lid via a machine screw and nut, held shut with a small spring.
     
  6. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    If you use modern dielectric oil or mineral oil, there's no hazard associated with it escaping, other than a slippery floor and the cost of replenishing it.

    Problem with the "paint can" loads I've seen (including the old Heathkit) is they are really 200W resistors cooled by the oil, so if you transmit long enough, 200W is all they can handle.

    My Bird Termaline 1200W load is rated 1200W 24/7; it's a continuous rating. It contains dielectric oil and also has a lot of heatsink fins, so it's cooled by two methods and it's 4x the size and weight of a Cantenna. But it has a handle on top so it's not difficult to carry around. It's also good to 3 GHz, so I can use it on UHF gear.
     
  7. W1BR

    W1BR Ham Member QRZ Page

    I agree, but once you get out of the 500 watt 82A class, the Bird price per watt increase seems exponential. Haven't lucked into a deal locally.
     
  8. K6BRN

    K6BRN XML Subscriber QRZ Page

    No pressure release valve is really needed (nor is it desirable), because the SO-239 connector is not hermetic. Even with a PL-259 attached. That said, oil WILL leak out of the "cantenna" just due to natural vaporization/recondensation. So a VAPOR PORT lower than the top of the SO-239 will make things lot drier at the coax. Simply drill a small hole in the paint can cover (1/8 inch will do) about 1.5 inches from the SO-239 and you are good to go. The top of the can will ALWAYS get wet with oil from vapor re-condensation, but oil will not wick up into the coax as it would with a real pressure relief valve, which would make the SO-239 the easiest vapor escape path. Do not fill the can to more than 1/2 inch below the lid and keep it level.

    Use a METAL bucket or small metal trash can with a solid bottom to keep the cantenna in, because oil will eventually leak down the sides. A plastic bucket is a bad idea - the oil will weaken it (depending on the type of plastic) and it could simply disintegrate. Happened to me when I put it into a plastic mop bucket. Lesson learned.
     
  9. KA9JLM

    KA9JLM Ham Member QRZ Page

    They come with a plastic cap. I left mine on.

    There is enough air leaking around the SO-239 that I don't think it will blow.

    You could fit a dog whistle, And let your dog tell you when to stop transmitting.
     
  10. W1BR

    W1BR Ham Member QRZ Page

    The SO-239 is part of the Waters load assembly and is a special sealed part designed for oil loads.
     

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