This is Curtsey of the:


Theory of Operation


Part One: Building and Maintaining Pressure.

The driving force behind any pressurized appliance, whether it be a lantern, lamp, stove or vintage heater is pressure. Pressure is built and maintained within the fount, or tank, of an appliance. Regardless of which appliance you're dealing with the basic principal is the same. The following illustrations are "butchered-by-me" representations of a Model 236 lantern, scanned from the 1937 Coleman Parts Catalog. I have deleted many parts of the original picture for clarity. Have patience-the pictures are large files and will take a little time to load.


Figure 1

The lantern shown in Figure 1 is ready for operation. Imagine the sun going down and you've just walked over to light it for the first time tonight. For this part of the discussion please note the pump plunger, the air stem, the pump cup and the check valve. Also note that the end of the air stem is seated inside the check valve.

When we get ready to use a lantern, the first thing to do is give the plunger a counter-clockwise twist, grab it and start pumping away. Simple enough but let's look at what happens.


Figure 2

In Figure 2 all we did was the very first step: turned the pump plunger a little counter-clockwise. Of course the picture is a little exaggerated but you see what occurred. With the pump plunger in the "CLOSE" position the bottom of the air stem is screwed into the check valve and will not allow air into or out of of the fount. What the twisting motion actually does is to unseat the air stem from the check valve. This being done, there is sufficient space around the base of the air stem for air to pass, and the valve's check ball will be keeping pressure in the fount.


Figure 3

In Figure 3 we're pulling the pump plunger back for the initial stroke. This pulling motion creates a small vacuum inside of the plunger cylinder, below the pump cup. The check ball at the bottom is firmly seated "up" so no air can be drawn out of the fount. In order to fill this vacuum air is drawn in around the plunger's cap, down the cylinder, and around the outside diameter of the pump cup.

When we have the pump plunger all the way to the top, the cylinder is filled with air and we're ready for the down-stroke.


Figure 4

The downward movement of the pump plunger forces the air in the cylinder down into the fount. The pump cup acts as a shield that, if operating properly, seals the plunger assembly coming down the cylinder. So, as the pump cup moves downward, the increasing pressure in the cylinder forces the check valve to unseat and the air passes through the valve, up through an air discharge tube and into the fount.

Wondering why the air discharge at the end of the pump cylinder is positioned near the top of the fount? It is a safety feature. Should the check valve fail while the appliance is under pressure, air (rather than fuel) will be released back up into the pump cylinder. Accordingly, the fount would depressurize without risk of igniting fuel outside the appliance.

 


Figure 5

Our fifth and final picture for this chapter represents a fully pressurized lantern. You'll notice a few things here. First, the pressure of the air has acted upon the fuel in the fount and caused it to flow upward into the tube in the center. This tube is called the "Fuel and Air Tube." The fuel has risen to the level allowed, that being to the (closed) main valve above the fount. Also note the ball in the check valve. Due to the extreme pressure inside the fount the ball is locked into the "up" position, thus keeping air from leaving the fount via the pump cylinder. When you're done pumping up the lantern the last step is the opposite of the first: twist the pump plunger fully clockwise into the "CLOSE" position. This will seat the air stem back down inside of the check valve and acts as additional protection against an air leak.

Simple mechanics and simple parts. But the steps we discussed can fail, leaving a lantern that doesn't work properly or not at all. The problem areas are three: the pump cup, the check valve and something not earlier mentioned, the filler cap gasket.

1. Pump Cup. Older ones are leather, new style are rubber. Their correct state is open like an umbrella and sufficiently tight against the cylinder. Oil is the lubricant and helps this seal. If the leather dries out, becomes too formed to the size of the cylinder or if a tear in the leather or rubber occurs it will no longer be able to create a seal for the pump's down stroke. You'll build little-or-no pressure because air will simply pass right by or through it instead of going down into the check valve.

2. Check Valve. The check valve can lock-up in the closed position or it can fail to seal, both of which can be a big problem. In cases where lanterns are stored for long periods of time with fuel in them and pressurized, the check valve can lock rock-solid in the up position. A dental pick or the sort can unseat them...this usually reveals the second and most common problem. The ball, and the seat it fits into, get corroded. If they don't fit perfectly the check valve won't seal properly. When you're done pumping up the lantern, lightly put your finger over the hole in the tip of the pump plunger. If it rises like it is possessed, your valve is leaking. Sometimes you can shoot carburetor cleaner down into it to get it clean enough to seal; usually it requires replacement.

3. Filler Cap Gasket. They just plain wear out over time. As the rubber hardens, the integrity of the seal lessens until it can no longer hold pressure. If you need to re-pump up the lantern after a few minutes you probably have a faulty filler cap gasket. The real bad ones are audible-listen for the air coming out at the fuel cap. Older fuel cap gaskets can be replaced while the new style, without the center screw, cannot.

That's all there is to pressurizing a lantern. Remember that most appliances are pressurized in the same manner. A stove tank is identical. Some lanterns, like the 242, don't have an air stem. Some lanterns make their own pressure by heat or by just shaking them. And the really old guys require an external pump. Those have a 2-piece fuel cap (without a gasket and it works!) and the inner piece holds the check valve. But, viewing the basic operation, they're all the same.

Part Two: From Fuel to a Vapor Mixture.


 


Figure 6

The above picture labels some things we'll discuss here so please look at it closely so you can follow along. First note in the above figure that the valve stem is closed (fully clockwise) and the tip cleaner stem is in the "up" position. Although exaggerated for our example also notice that the very tip of the tip cleaner is pushed up and through the top end of the generator. Also realize that red indicates a fuel and air mixture coming up through the Fuel and Air Tube, not pure fuel.

The pictures shown here don't give you an explanation of the Fuel and Air Tube. The "F&A Tube" is fitted to the bottom of the valve and extends down into the fount. Very old appliances had a slightly different set-up which was nothing more than a small hollow tube called the "pick-up tube." The more modern version consists of three pieces: the tube, a spring and a rod. The tube has a hole at the very bottom for fuel pick-up. There are also passages near the top to introduce air into the valve. The rod is used to meter the amount of fuel that is picked up at the bottom and the spring acts as a counter to the downward force applied to the rod by the valve stem. When we open the valve, that is to turn the stem 1/4 counter-clockwise, the conical end will pull back out of the valve body. The first thing this does is to relax the downward pressure on the F&A Tube rod. As the valve is progressively opened more fuel and less air will be delivered to the valve. This means that very little fuel is applied when you first crack the stem open (very lean) and when the valve is 100% open you'll have a very rich mixture. The other result of turning the stem 1/4 turn is opening of the passage from the valve body up to the generator. The amount of fuel mixture allowed to pass through the valve body is proportional to how much the valve is opened. The fuel will pass through the valve body, up past the eccentric block and into the generator:


Figure 7

Now a real tip cleaner stem in the "up" position probably will not stop fuel like the picture shows. Also, the generator in the picture appears hollow except for tip cleaner stem. Actually there are small coil springs or formed paper tubes or asbestos (older ones such as the Q99) or combinations thereof inside. Their purpose is to act as a heat transfer device primarily; they also act as a filtering medium. These devices, coupled with the thin-walled brass generator are essential to rapid fuel vaporization.

Please notice what is above the generator: air. As important as fuel is good air flow. Now remember that this picture comes from an old Coleman book; this type of solid frame set-up was quite common on single mantle lanterns until the early '50s. With double mantle models, and single mantles starting with the 200, there is a crooked tube (air intake tube) that the tip of the generator goes up into. Whether from the side air tubes as shown or a "crooked" air tube on other models, the point here is that an unrestricted supply of air is directly above the tip of the generator.

We have pressurized fuel at the top of the generator and we have a good supply of air above the generator. Let's turn the tip cleaner stem down and do some mixing!


Figure 8

The orifice at the tip of the generator is very small. This orifice is usually 0.005" to 0.012" on most Coleman generators. Because there is a great deal of pressure behind the fuel and the orifice is providing a great deal of resistance to it, the generator "shoot" fuel up into the lantern...much like putting your finger over the end of a garden hose. Actually an "uncapped" system's generator will shoot a stream of gas a couple of feet in the air.

Now that we have a stream or spray of fuel coming out of the top of the generator it is a good time to stop and discuss fuel vapor. "Fuel," which for all practical purposes we can consider gasoline, will vaporize at room temperature. Actually it has a -45 degrees Fahrenheit flashpoint which means as long as it is above that temperature it will produce vapor. Our cold lantern will spray vapor, sure, but mostly what initially will come out is a mist of gasoline.

Wondering why kerosene lamps and lanterns need to be pre-heated? Kerosene has a flash point of 100 degrees which means it needs to reach that temperature before it will produce vapor. Also, kerosene's vapor is 30-50% higher in density than gasoline's. Kerosene needs more air (or less fuel) than does gasoline so kerosene generators have a smaller orifice. Another interesting item is that kerosene lanterns generally do not have Fuel and Air tubes.

This fuel and vapor supply will be shot up into an area we can generically call a mixing chamber. On double mantle lanterns the top piece of the burner assembly is called the mixing chamber. On single mantle lanterns like the 200A the fuel is shot into the venturi and U-tube. Makes no difference what we call it-the fuel is sprayed up and mixes with air. The shape of the mixing chamber will direct this mixture around and down into the burner tube, cap and screen.


Part Three: Producing Light.


This last chapter takes us to the working end of the lantern: the mantle. Fuel is being forced up through the lantern's internals by pressurization and a good fuel/air mixture is being released out of the burner tube. Now we can talk about the "sock" that fits on the burner cap and gives us our light.


Figure 9

So what exactly is a mantle and why does it do what it does? Since I am not a chemist, engineer nor metallurgist and I can only give you the information that I found after much research...and the information that made sense to me!

Mantles are a fabric material that have been saturated with metallic salts. Most modern mantles are saturated with Yttrium and Cerium nitrate. By pre-burning the mantle, the fabric burns away leaving a ceramic shell of Yttrium and Cerium dioxides and it is fragile.

Yttrium has a very high melting point and incandesces when heat is applied to it. The light the lantern generates is not from the actual pre-mixed flame contained in the mantle, rather, it is the result of the Yttrium and Cerium being heated by that pre-mixed flame.

Old mantles, and some of the currently-made off brand ones, are saturated with Thorium rather than Yttrium. I point this out because Thorium is radioactive. All current Coleman mantles are made with Yttrium. You should always pre-burn mantles outside with good ventilation and avoid breathing the fumes. But you should also take caution in storing and handling mantles made with Thorium. Very few mantle packages will tell you if they're radioactive.

So back to the lantern. The mixture of fuel and air directed down the burner tube has been ignited. Relatively speaking, the surface area on the inside of the mantle is pretty large. This means that the flame is being applied to a good amount of the metal oxides. And, because of the way these metals react to heat, this will produce the intended result: light.

Please remember that this was written by a simple guy--much of the "hard core" theory was either glazed over or omitted entirely. After all, I'm not trying to invent a pressure device. I'm just trying to give you a basic idea of how they work.