The pressure compensator and accumulator comprises a casing having ports at opposite ends. A hermetically sealed air chamber means of elastomeric material is loosely housed within the casing. The device is serially inserted in the flow line by connecting one port to an open end of the flow line, and connecting the adjacent open end of the flow line to the opposite port, whereby flow takes place through the casing from one port through the opposite port. Means are provided to prevent the blocking of the outlet port by the air chamber means when the means moves toward the outlet port under the influence of the flow.