Abstract: An apparatus for exchanging pressure energy between a fluid having a high energy content as a result of pressurization, and a fluid having a relatively lower pressure. The apparatus includes a rotor which has a plurality of spaced tubes extended in substantially parallel array over a major portion of the rotor length, and each having a separatory member movably mounted therein for reciprocatory displacement in the respective tube. Each of the fluid conveying tubes has its opposite ends movably but sealingly received in recesses in; floating rotor seal plates. Each seal plate further includes an arcuate port which completes the opening formed by both the recess and port through the seal plate. The opposite side of each seal plate from that which contains the recesses into which the respective tubes extend bears sealingly against a fixed stator block.