My First Primus

Discussion in 'Stove Forum' started by Doug's Kid, Nov 8, 2019.

  1. Doug's Kid

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    Just obtained a Primus 51, my first of this classic type. Stamped "AB" on the bottom, so if I'm doing the math right that means made in 1946, right? I first notice this style stove in various historical dramas, such as those covering polar expeditions. Very cool that the design has lasted so long. Kind of like revolvers in the firearms world, and turtles in nature. All designs that are not flashy, and which have been taken for granted long before the oldest person living today. Some would argue these have all been surpassed by more recent designs. Yet they all just keep plugging along, monotonously achieving their design purpose, year, after year, after year. That is my definition of a successful design.

    I've been reading up on the type here, and watching various youtube videos (e.g. BernieDawg), but I'm still pretty much a newbie to stoves in general, and definitely a newbie regarding the Primus. I've go the following questions... if anyone cares to educate me.

    1. This burns only kerosene, right? Or are there other fuels that are safe to burn?
    2. I don't understand how the fuel, which starts as a liquid in the bottom of the tank, gets transported to the burner. A Svea 123 uses tank pressure, but also a wick, to get fuel to the nipple, but this doesn't have a wick. I can only assume that the stove relies on vaporized fuel in the airspace above the liquid fuel. If so, then apparently that doesn't work with the white gas in a Svea 123. Why not?
    3. Rather than controlling the output of the burner directly with a valve that limits the flow of the fuel to be burned, this stove controls the flame by bleeding off the pressure that is forcing the fuel into the burner. But I'm thinking it isn't just air that you bleed off, but vaporized fuel too. Since this is venting just a few inches from the burner flame, doesn't that present a fire risk?
    4. And if it really is venting fuel vapor, isn't that wasteful, and polluting? Clearly I have a fundamental misunderstanding somewhere.
    5. The ring that sits on the three supports has six indentations for the tops of the supports. Every other indentation has little ears which presumably can be crimped around the top of each support, to prevent the ring from falling off in use. I assume this feature is meant for people who set this up in a more permanent situation than a camper would be in. Is that right?
    6. My understanding is that there is a rubber pip at the bottom of the pump tube that holds pressure. Is this considered a NRV? Given the stove is 73 years old I don't plan to test fire it until I've replaced that. Any recommendations on the best place to obtain parts and tools for this? I see Juliands on ebay looks to have what I'd need.
    That's all that I can think of for now. Probably have more questions later.

    Thanks in advance for any information you care to send my way.
     
  2. abbahco1

    abbahco1 Subscriber

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    1. This burns only kerosene, right? Or are there other fuels that are safe to burn? Kerosene only.
    2. I don't understand how the fuel, which starts as a liquid in the bottom of the tank, gets transported to the burner. A Svea 123 uses tank pressure, but also a wick, to get fuel to the nipple, but this doesn't have a wick. I can only assume that the stove relies on vaporized fuel in the airspace above the liquid fuel. If so, then apparently that doesn't work with the white gas in a Svea 123. Why not? Liquid kerosene is pumped up the central burner tube. The pre-heated burner gasifies it and the vapour mixes with air as it exits the nozzle.
    3. Rather than controlling the output of the burner directly with a valve that limits the flow of the fuel to be burned, this stove controls the flame by bleeding off the pressure that is forcing the fuel into the burner. But I'm thinking it isn't just air that you bleed off, but vaporized fuel too. Since this is venting just a few inches from the burner flame, doesn't that present a fire risk? The tank contains only air and liquid kerosene, so you are only releasing air from the tank when you open the screw. That's why thee is no fire risk (unlike petrol/gasoline).
    4. And if it really is venting fuel vapor, isn't that wasteful, and polluting? Clearly I have a fundamental misunderstanding somewhere. It's venting air only- there is no gas until the kerosene hits the pre-heated burner.
    5. The ring that sits on the three supports has six indentations for the tops of the supports. Every other indentation has little ears which presumably can be crimped around the top of each support, to prevent the ring from falling off in use. I assume this feature is meant for people who set this up in a more permanent situation than a camper would be in. Is that right? That's right.
    6. My understanding is that there is a rubber pip at the bottom of the pump tube that holds pressure. Is this considered a NRV? Given the stove is 73 years old I don't plan to test fire it until I've replaced that. Any recommendations on the best place to obtain parts and tools for this? I see Juliands on ebay looks to have what I'd need. The non-return valve has a cork pip that seats and seals the inside of the valve. After 70 years or so this is shot and needs to be replaced. Getting the non-return valve out requires a well-crafted tool (good ones available on Ebay, supplied from Japan).
    7. If it is stamped "AB", then your stove dates from 1937.
     
  3. Simes

    Simes Subscriber

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    I think the only two things missing at this point are the condition of the filling cap gasket, if this has hardened to you"ll probably not be able to maintain pressure in the tank. If you are ordering spares then you may wish to add a couple of those.

    The jet may also be a little enlarged, not a serious problem if gou wish to get the stove running, but it will run rich at higher pressures and soot pots.

    And lastly the condition of the pump leather, (ok more than two issues) should be a nice cup shape and pliable, if a soak in light oil overnight doesn't refresh it or it's worn or torn then add one to the spares list.

    Fourth, if you want to make it nice and shiney avoid Brasso, look for autosol

    Fifth, nice pictures brewing tea or coffee by your neareat lake/seashore/ wood we would love to see.
     
  4. Ed Winskill

    Ed Winskill United States Subscriber

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    Splendid questions, and great answers. Most of the questions had occurred to me from time to time....
     
  5. Retro Camper

    Retro Camper Subscriber

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    Congratulations on obtaining your first classic camp stove. You are in the best place for guidance and encouragement and will soon be thinking about the next stove you want!
     
  6. kerophile

    kerophile United Kingdom SotM Winner Subscriber

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  7. HaakonJ

    HaakonJ Subscriber

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    @Doug's Kid

    The thread in the link below shows the inside of a tank, where part of the bottom is cut out. I believe one reason for your misunderstanding is that you are not aware of the riser tube that extends from the burner to the bottom of the tank. This way, the tank pressure can force liquid kerosene up through the burner, and you get 100 % kerosene vapor exiting the nozzle.
    Valor No.51 Dissection.

    There will always be a small concentration of kerosene vapor inside the tank's air pocket, the same way there will always be water vapor above the surface of liquid water, or even iron gas above the surface of liquid iron. When you release the tank pressure by opening the tank, there will be a small amount of kerosene vapor coming out with the air, but the concentration is so low that you would probably not be able to light it if you wanted (but I wouldn't try it! :lol:). You may smell this kerosene when venting the tank, but I wouldn't worry about pollution or wasting fuel.

    Good luck with your fettle!

    Håkon
     
  8. Doug's Kid

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    Yes, you got that exactly right. I was thinking about it this morning though, and figured out on my own (before reading this thread) that there must be some kind of tube inside the tank, which delivers the fuel. So I may be slow, but I figure things out eventually. Thanks for your confirmation of how it is designed.

    The other thing that makes sense now is the fuel tank shape. A 123 has a concave tank bottom, while the Primus is convex. But the 123 has the wick which will spread out to the low points on the tank perimeter, allowing fuel pick up. The low point on the Primus is in the middle of the stove, right under the riser tube, so it will be able to pick up fuel right up to the bitter end, with no wick needed.

    I did do the math right, it is a 1946 stove. What I did wrong was typing the code as AB when it is actually AK. I think when I was considering buying the stove, and trying to read its code from a photo on line, I thought it looked like AB at first, and so I had that in my mind when I was typing.

    Nobody commented on the possibility of alternate fuels... but looking up flash points of kerosene vs. white gas makes me think that it is likely dangerous to attempt running it on white gas, what with the venting of tank gases just inches from an open flame. I have no need to avoid kerosene, I'm just looking for a more complete understanding of the functioning of this stove vs. a white gas stove.

    I've washed the stove with soap and water, to get some of the soot off it. I'm undecided yet as to whether I'll polish it up at all, or just leave it with its patina. Shiny brass is definitely pretty, but part of the beauty of these mechanisms is their functionality and usefulness. The patina is a constant visual reminder of the stoves utility and purpose, kind of a badge of honor. What is probably going to happen is that I'll get more stoves of this type, so I can have some shined up and some in working colors.

    Thanks all for your excellent responses.
     
  9. Ed Winskill

    Ed Winskill United States Subscriber

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    You are quite right about the reason not to use petrol fuel in these stoves; your path of reasoning is borne out by experience.

    The problem is not that you will get a fireball if you use white gas and vent the tank to shut off. In fact, you can burn white gas in these keroburners without a problem until-- the day you do have the problem, and an explosion.