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HOW A DRYWASHER WORKS
Dry, gold-bearing material is fed onto the grizzly screen, usually with the aid of a shovel or bucket. The thinner material, such as dirt and small gravel, falls-through the grizzly screen and into the hopper. Larger material, such as rocks and sticks, rolls-off the grizzly and back onto the ground. Material from the hopper is then fed by gravity into the riffle tray, through an opening in the bottom of the hopper. The rate of flow from the hopper to the riffle tray is usually regulated by an adjustable door or shutter on the bottom of the hopper. As the material flows across the riffles, air is blown through the bottom of the riffle tray. Lighter material is kept in a state of suspension; riding on a cushion of air until the material eventually leaves the riffle tray. Heavier material (such as gold) is not lifted by the air and gets trapped by the riffles.
DRYWASHING ADVANTAGES
· Drywashing is one of the fastest methods for recovering gold from dry material.
· Operating a drywasher can be a good form of physical exercise.
· Drywashers can be "home-built" very economically.
DRYWASHING DISADVANTAGES
· Weather conditions such as wind or rain can greatly effect the operation of a drywasher.
· Drywashers can be used effectively only if the ground is almost completely dry.
· In some cases, drywashers can be "bulky" and difficult to transport.
· Operating a drywasher can be a "dirty job"; as most drywashers generate a great deal of
airborne dust and dirt when in use.
· Gasoline powered drywashers have a tendency to be very noisy.
· As with most mechanical devices, drywashers require a certain amount of maintenance and are
prone to frequent mechanical failures.
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