Extremely compact design particularly suited to offshore applications. Designed to give operation and standby facility within a single vessel. Interlocking changeover mechanism prevents complete flow shut-off. Very compact valve mechanism resulting in weight and space saving. Low pressure loss achieved by straight-through flow path with minimal changes in flow direction. A high surface area pleated screen with maximum effective filtration area is positioned directly in the flow path. Weight saving makes this particularly cost effective in higher alloys.