A common problem was the small check value in the bottom of the pump. If this fails it will allow gas to pass the pump piston and fill the chamber on top of the leather cup, now when you lift the pump gas squirts out the top of the pump all over you and as your holding an ignited blow torch you of course catch fire. Now your on fire the first thing you do is throw the burning blow torch away, you can see the disaster unfolding.
How Does A Gasoline Blow Torch Work?
It is very important to the operation of a blow torch that the torch be able to hold pressure to ensure a good, hot and strong flame. The fuel tank is filled to about 3/4 of the capacity of the tank. With the fuel valve closed and all tank plugs in place, the pump is used to pressurize the tank with air. This air pressure drives the fuel up through the wick tube to the burner head.
The wick tube is part of the pipe that connects the tank to the burner head and it sticks down into the tank to draw out the fuel. In the wick tube is a cotton wick that sticks in the tube about three inches with an additional three to four inches that lay in the bottom of the tank. The torches were designed to be usable in a variety of applications which requires them to be used at almost all conceivable angles of orientation. As the fuel in the tank gets used up, at some angles the wick tube will not be immersed in the fuel and the torch will go out. The wick, by way of capillary action, sucks the fuel out of the tank and into the wick tube.
Just above the wick tube and inside the pipe nipple is a screen type filter, which acts to filter small impurities out of the fuel before it, is burned which helps to keep the orifice from being plugged. An integral part of the burner head is a fuel passageway called the undervein or evaporating chamber. When the torch is burning, the burner head is very hot. Any gasoline in the undervein will be rapidly evaporated due to this intense heat. By locating the undervein at the bottom of the blow torch head, the fuel will be kept hot enough to vaporize the fuel even on cold days and/or in cold environments. The evaporation process builds up pressure between the wick and the burner head. The only way out of the torch is via the orifice, where the fuel is ignited and burned. It is this buildup of pressure that causes the roaring, blue flame in a blow torch. It is in fact, what makes the blow torch...blow.
In the later production brass blow torches, you will notice many holes in the burner head. Some of them will be close to the rear of the torch, while others will be found at the flame end of the torch. During the operation of the torch, the observer will notice small flames protruding from the holes in the flame end of the burner head. This group of holes are there to keep the burner head hot during operation. This in turn ensures that the torch will stay burning even in cold surroundings. The holes at the orifice end of the burner head function as an air intake so the evaporated fuel can mix with air, which is vital for combustion. In some of the Otto Burnz blow torches, the air intake is a triangular shaped hole rather than the round holes common in other makes of torches.
It is vital for the burner head to be at a high enough temperature for the torch to work properly. If the burner head is not hot enough, the flame will be yellow and wimpy rather than blue and roaring. Another symptom is that the raw gasoline will shoot out about three feet and catch on fire. What you have is a flame thrower and not a blow torch! If this happens, it is an indication that the burner head is not hot enough and should be shut down and reheated to the proper starting temperature.
During operation, the wick tube heats up due to its physical connection to the burner head. This heat is conducted into the tank where it heats up the raw gasoline, which helps maintain pressure inside the tank as the fuel is burned. At no time should the tank get so hot that it becomes uncomfortable to hold your hand on the front of the tank. The automatic pressurization is why it is not good to see how much pressure you can pump into a torch by overpumping it. It accomplishes nothing by doing this. You may actually cause a leak to develop!
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