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How a Lantern Works

It is not magic nor is it difficult to understand. Pressurized lamps, lanterns, stoves, irons and burners all use simple mechanics and basic principles for operation.

This "theory" chapter will discuss a Coleman® lantern. The principals are the same for just about every pressurized gasoline or kerosene lamp or lantern, regardless of manufacturer. Many of these functions also apply to stoves, however, a stove creates flame rather than light so we will also cover the basics of how a stove works at the end of the discussion.

Part One: Building and maintaining pressure.The driving force behind any pressurized appliance is pressure. Pressure is created and maintained within the fount, or tank, of an appliance.


Fig 1

Figure 1 shows the fount of a single-mantle lantern. Imagine this as any lantern or lamp sitting on any table, ready to be lit.

The pump and the check valve are used to create pressure. The fuel filler cap gasket is important for maintaining the pressure.

I'd like you to notice the pump, air stem and check valve first. The pump is fully clockwise, or "closed," and this means that the threaded air stem is all the way down and fully seated in the check valve. When we are to use a lantern the first thing we do is give the plunger a counter-clockwise twist, grab it and start pumping away. Simple enough but let's look at what happens.


Fig 2

In Figure 2 we've taken the first step and turned the pump plunger counter-clockwise.

The graphic is over-exaggerated for clarity but you see what occurred. The twisting motion of the pump actually turns the air stem and unseats it from the check valve. There is now sufficient space at the bottom of the air stem for air to pass.


Fig 3

In Figure 3 we're pulling the pump plunger back to pump the lantern.

This pulling motion creates a small vacuum inside of the plunger cylinder, below the pump cup. The check valve at the very bottom has a small ball bearing in it that is being pulled up into the closed position with this motion. This helps create the vacuum because no air can be drawn out of the fount. In order to fill the vacuum, air is pulled down the pump cylinder and around the outside diameter of the pump cup.


Fig 4

Figure 4 illustrates what happens when you press the pump plunger down to pump the lantern.

During the down-stroke the pump cup forces that air in the pump cylinder into the fount. As the pump cup moves downward, the increasing pressure in the cylinder forces the check valve (down) to unseat it, and air passes freely through the valve. After the check valve, air travels up through an inlet tube and into the fount.

Wondering why the air inlet tube the end of the pump cylinder travels "up" to near the top of the fount? This is a clever 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. With a burning mantle or flame, it would be much better to have air coming out of the pump than fuel!


Fig 5

After (let's say) 30 pumps, Figure 5 shows what the lantern looks like now that it has been pressurized and is ready to operate.

First note that the constantly (30 times in this case) increasing amount of air has put pressure on the fuel and this pressure has caused it to flow upward into the tube in the center. 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 (and pressure) from leaving the fount via the pump cylinder.

When you're finished pumping up the lantern the last step is the opposite of the first: turn the pump plunger fully clockwise to "CLOSE." This will re-seat the air stem in the check valve and acts as additional protection against an unwanted release of air.

Before we leave Figure 5 we should discuss one part inside the fount that will be important later in the lesson. The fuel and air tube is fitted to the bottom of the valve and extends down into the fount. Older appliances have nothing more than a small hollow tube called the "pick-up tube." The fuel and air tube has a hole at the very bottom for fuel and passages near the top for air. The rod is used to meter the amount of fuel versus air and the spring acts as a counter to the downward force applied by the valve stem.

When the valve is off the conical tip of the valve stem is forcing the rod down. When we turn the valve stem counter-clockwise, the conical end will pull back out of the valve body and relax the downward pressure on the rod. As the valve opens, more fuel and less air will be delivered to the system. This means that a very lean mixture is applied when you first crack the stem open and an increasingly rich mixture as the valve is opened.. This allows the lantern to use a lean mixture during initial lighting and then a standard mixture during normal operation.


Part Two: From gas to gas. That doesn't make a lot of sense but it is exactly what a lantern, lamp, stove or burner does.


Fig 6

Refer to Figure 6 and note that the pressurized fuel is resting below the closed lantern valve, which means that the valve stem is fully clockwise. Also notice that, although exaggerated for illustration purposes, the tip cleaner stem is in the "up" position causing the tip cleaner to be exposed above the generator. Red indicates an air and fuel mixture, not pure fuel.

When we open the valve, that is to turn the valve stem counter-clockwise, the conical end will pull back out of the valve body. As previously discussed this will relax the downward pressure on the fuel and air tube rod. The other result of this action is allowing pressurized fuel to pass from the fuel and air tube, through the valve body and up into the generator. The amount of fuel mixture allowed to pass is proportional to how much the valve is opened.


Fig 7

Now a real tip cleaner stem in the "up" position probably would not stop fuel as the picture shows. Also, the generator in the picture appears hollow except for tip cleaner stem. It has small coil springs or formed paper tubes or a combination of them inside. The reason for these is for heat transfer and to provide resistance to the fuel flowing through the generator. They are essential to rapid fuel vaporization.

Please notice what is above the generator: air. As important as fuel is good air flow. The graphic used is just one way to mix fuel from, and air above, the generator. Your lantern probably has a more common "air intake tube" that has a crook in it and the tip of the generator enters this bend. 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.


Fig 8

The orifice of the gas tip at the end of the generator is very small, usually 0.005" to 0.012". Because there is a great deal of pressure inside the hot generator and that small orifice is offering a great deal of resistance, the generator will "shoot" fuel up into the lantern, much like placing your finger over the end of a garden hose. An "uncapped" generator will shoot a stream of gas a few 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 is for all practical purposes gasoline, will vaporize at room temperature. It has a -45 degrees Fahrenheit flashpoint so as long as it is above that temperature it will produce vapor. Our cold lantern will spray vapor, sure, but mostly what comes out initially is a mist of raw gasoline.

This fuel/vapor enters 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 enters into a venturi. It 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, burner cap and screen.

Wondering why kerosene lamps and lanterns need to be pre-heated? Kerosene has a flash point of 100 degrees Fahrenheit which means it needs to reach that temperature before it will produce vapor. Also, kerosene vapor is 30%-50% higher in density than gasoline vapor. Kerosene needs more air (or less fuel) than does gasoline so kerosene generators have a smaller orifice. Another interesting item is that kerosene lanterns have basic fuel pickup tubes rather than fuel and air tubes.


Part Three: Producing Light.Finally we come to the end where the fuel vapor is ignited inside the mantle to produce light.


Fig 9

The mixture of fuel and air directed down the burner tube comes out the burner cap and to the mantle. When ignited, the flame is restricted to the inside of the mantle during normal operation. This flame will cause the mantle to incandesce which is why the mantle is much brighter than just a flame.

So what exactly is a mantle and why does it do what it does? Since I am not a chemist or metallurgist, I can only provide the information I found after much research...and the information that made sense to me.

Mantles are a fabric material saturated with metallic salts. Most modern mantles are saturated with Yttrium and Cerium Nitrate. By pre-burning the mantle, the fabric burns away to leave a ceramic shell of Yttrium and Cerium dioxides and is veryfragile.

Yttrium has a very high melting point and incandesces when heat is applied to it. The light the lantern generates is not from the flame contained inside the mantle, rather, it is the result of the Yttrium and Cerium being heated by that 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. Always pre-burn mantles outside with good ventilation and avoid breathing the fumes.

Please understand that these are the basics of how a pressure lantern works. It has been simplified, obviously, for the layman writer and the layman reader. They are relatively simple devices and keeping this simple is a good thing.


Part Four: Stoves in a Nutshell.Just about everything you just read on lanterns also applies to stoves, up to the point where fuel is shot out the end of the generator. You can even imagine tilting all the graphics above by 90 degrees and that lantern being a stove tank.

In a stove, the pressurized fuel is applied to the manifold rather than the burner cap. It travels through the manifold and to the burner(s) where the bunsen effect occurs to produce flame.

The Bunsen effect is really nothing more than using the correct amounts of gas and air to produce a very high temperature flame with little luminescence. The air-gas mixture enters the burner where it is spread evenly to a pattern of small outlets. By igniting the fuel from these outlets we get a pattern, usually a small circle, of intense flame.

Copyright 2010. All rights reserved.
Information may not be copied, printed or otherwise reproduced without the written consent of the owner.
Coleman is a registered trademark of The Coleman Company, Inc.

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