Abstract: An excess pressure and/or excess flow/temperature shutoff valve comprising a valve housing having an axial bore therethrough with inlet and outlet ends, a portion of the bore being enlarged to form a valve chamber, and a spool movable in the valve chamber and having a sealing fit with the walls of the chamber. In the event of an upstream pressure increase of predetermined magnitude, the spool is adapted to move from an open position in which it permits flow of fluid through the bore to a position wherein additional spool area is exposed to the upstream fluid pressure, whereupon the spool is adapted to move further downstream to a shut off position for blocking the flow of fluid through the bore. The valve may be optionally equipped to shut off the flow of fluid in the event of a downstream pressure decrease as a result of excess leakage and/or an increase in fluid temperature in excess of a predetermined value.