Pressurised water filter - with small bore opened in absence of filter element removed for cleaning

A filter for insertion in a pressurised water system, specially for hydraulic properties to support the roof strata in mines, inludes a filter element consisting of a stack of annular laminae, leaving a system of parallel slots. The preferred flow direction is radially inward. A small bore through the housing at an abutment of the element is normally sealed by two O-rings. If the personnel is too lazy to clean a clogged filter element, and throws it away, a jet of water leaves through the bore. This enforces the use of a clean filter and saves the ruin of expensive hydraulic equipment.