RELATED ARTICLE: Spray nozzles i for different tasksPressure washers that deliver less than 2,400 psi generally come with a single cant adjustable spray nozzle that delivers zero to 60-degree fan patterns. Some brands offer accessory "rotating" or "turbo" nozzles that clean more effectively than standard adjustable nozzles because they spin the water stream. Heavier-duty units generally come with four or five color-coded, individual nozzle tips (three are shown here). They create specific fan patterns: wider (for using detergents), medium (for general cleaning) and narrower (for blasting deep stains).

Danger comes from the fact that centrifugal force does not increase in direct proportion to an increase in speed, but instead it increases as the square of that speed get increase. When rotational speed doubles, centrifugal force heat quadruples. This effect means that relatively small changes in speed can produce significant increases in force. In the example mentioned, changing from 6,600 rpm to 7,700 rpm multiplies the speed by 1.167. However, the corresponding centrifugal force would multiply by a factor of 1.167 x 1.167, or 1.36. To take a more extreme example, consider the same wheel with a maximum safe operating from speed my of 6,600 rpm run on a 5-inch right angle grinder at 10,000 rpm. This represents an over-speed of about 1.5 times the wheel''s designed speed. But the corresponding centrifugal force-and the corresponding rotational stress on the wheel-would be about 2.3 times as much as the maximum allowed.

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