A drywasher is a piece of machinery used in small-scale mining operations. While traditional mining equipment requires large volumes of water to separate gold from rocks and soil, a drywasher separates gold and other metals using a dry sorting process. These machines are primarily used by hobbyists and casual miners due to their small capacity and relatively low sorting rates, and are not designed for commercial or industrial mining projects.
The standard drywasher consists of two bins supported by a metal frame. These bins are arranged at a shallow angle to one another, with the bottom bin sitting parallel to the ground. The upper bin, known as the hopper, features a mesh screen along the bottom. As miners shovel dirt and rocks into the hopper, the mesh screen allows small particles to pass through into the bottom bin, while forcing large rocks and debris out and onto the ground.
The bottom bin, which is known as the riffle tray, features a cloth or canvas bottom. A blower or fan directs air up from the bottom of the riffle tray, and the fabric tray bottom allows this air to enter the tray. The air pressure from below causes dirt and other lightweight particles to blow away or exit the tray, but is not strong enough to move gold and other metals. Instead, these metal particles remain in the drywasher, where they can be collected by hand from the riffle tray.
Miners can choose from two basic types of drywasher machines, with each device distinguished by the method of air production. The most basic models include a bellows, which is operated using a manual crank. Some also include a battery pack for faster air blowing, or for added air pressure. More advanced drywashers include a separate motor, which incorporates both air flow and vibration to sort materials in the riffle tray. These models require a fuel source, such as gasoline or propane, and tend to cost more than bellows units.
One of the primary advantages to mining with a drywasher is the portability and convenience offered by these devices. Some models are small enough to wear on the back like a backpack, allowing hobbyists to mine at almost any location. These units are also relatively affordable, and can even be made at home using basic materials. Finally, basic drywashers include very few parts, which reduces maintenance requirements and minimizes the learning curve associated with this equipment.