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A pressure lamp is a liquid fuel lamp featuring a pouch shaped incandescent fabric mantle that provides an intense light when heated. This kind of lamp functions by feeding a pressurized mixture of liquid fuel and air into the inside of the pouch where it is ignited. The lamp fuel is stored in a small tank that typically forms the lamp base and is pressurized by means of a integral hand pump. A fuel flow dial allows the intensity of the lamp to be adjusted to suit lighting requirements. The mantle and fuel feed mechanism is enclosed by a glass hood and topped with a vented roof typically fitted with a carrying handle.
Pressure lamps require only a source of liquid fuel and a primer to produce a light as intense as any modern electric variety. The principle behind these versatile lamps is the tendency of a fabric coated in certain chemicals to glow or incandesce with a brilliant light when heated sufficiently. In a pressure lamp, this is achieved by feeding a high pressure mixture of liquid fuel and air into the interior of a pre-burned, chemically treated fabric mantle and igniting it. The resultant flame causes the mantle to incandesce with a light far stronger than that of the ignition flame. The fuel used in these lamps is typically kerosene although gasoline varieties have been successfully produced.
The base of a pressure lamp is usually formed by small metal fuel tank fitted with an integral hand pump to pressurize the fuel. A thin tube leads up from the tank into a vaporizer and mixing chamber. A larger tube leads up out of the mixing chamber to the top of the lamp where it is bent into a U shape and led down to a ceramic nozzle with a thin groove cut into its holder. The mantle is tied over the nozzle with a draw string which lies in the groove. Prior to use, the mantle is burned, thereby leaving the characteristic brittle skeleton behind.
To light the lamp, the fuel in the tank is first pressurized with the hand pump. The vaporizer and mantle are then preheated with alcohol burned in a small build-in primer container. Once the preheat is completed, the fuel flow dial is opened, thereby allowing fuel to be pushed under pressure into the heated vaporizer where it expands and mixes with air in the mixing chamber. The now thoroughly mixed fuel and air vapor travels down to the ceramic nozzle where it exits within the mantle interior. The high pressure exit of the gas from the vaporizer and turbulence when mixing with the air are responsible for the well known hissing sound these lamps make while burning.
At this point, the pressure lamp is lit, thus igniting the fuel/air mixture and resulting in a hot, clean flame within the mantle. The heat from the flame causes the mantle to incandesce and produce the lamp's characteristic brilliant white light. As long as there is a supply of pressurized fuel in the lamp, this process is self sustaining from that point. The mantle and tubing are surrounded by a glass hood to shield the lamp from wind and prevent accidental contact with the hot mantle. The lamp is topped with a vented roof usually fitted with a carry handle. Caution should always be exercised when handling a burning pressure lamp because the glass hood, roof and handle, if left standing upright, will be extremely hot.