Abstract: The present invention includes a piston valve for charging and discharging a first fluid chamber. The piston valve includes a piston shaft and a ring comprising a seal element. The piston shaft has a first end and a second end with the first end including a counter bore having at least one vent. The ring is disposed within a cylinder and the seal element is disposed intermediate the piston shaft and the ring. The piston valve may be used for intensification purposes such as in a high pressure high temperature hydraulic cartridge.