Hydrocyclone
A hydrocyclone or sand separator is a device which utilises centrifugal force to separate sand or other heavy particles out of water. The separated material drops down into a tank or reservoir where it can be removed later or in the case of in-well separators, the separated sand drops into the bottom of the well. It is not a true filter, since there is no physical barrier to separate out the particles, but it is often used upstream of a filter to first remove the bulk of the contaminant, where the filter does the final cleaning. This type of design reduces the time required to flush and clean the filter.