A pressure gauge and/or relief valve which may be used in a single-use fluid system, such as a sterilizable fluid system. The pressure gauge and/or pressure relief valve may be configured to measure and to relieve fluid within a fluid-containing structure, the pressure gauge relief valve including a housing having a first end, a second end, and an inner surface defining a passage between the first end and the second end, a movable element movable within the passage, wherein the housing first end is configured to be coupled with a fluid-containing structure, the housing second end is spaced from the housing first end; and the movable element is movable with respect to the housing to indicate pressure therein and to allow fluid to pass between the movable element and the inner surface of the passage at a selected pressure.