This document provides mechanical seals that include one or more rolling diaphragms. In one example embodiment, this document provides double rolling diaphragm seals that are usable in conjunction with various types of equipment including, but not limited to, accelerated life testing systems. In such a context, the double rolling diaphragm seals facilitate high-speed linear modulation of a variable volume pressure vessel, while maintaining precise volumetric control. Such an arrangement can facilitate an essentially frictionless linear actuation system having a long stroke, long service life, and precise volumetric control. In addition, this document provides linear actuator systems that can be used in adverse environmental conditions.