The PressureGuard™ Self-Contained Hydraulic Emergency Shutdown Systems are designed to provide reliable valve shutdown capability when an external power source is either not available or not dependable. The PressureGuard system has proven to be highly successful in years of field service under some of the most demanding operating and environmental conditions. The module can be used with either rotary or linear spring-return hydraulic operators to provide a fail-safe system adaptable to ball, plug and other quarter-turn valves as well as reverse-acting gate and other linear operated valves. The PressureGuard system offers built in temperature compensation and pressure relief. It provides the foundation for a flexible system utilizing a variety of available sensing and control options.