A pressure exchanger system comprises at least one pair of pressure vessels (Fig 2, 101a, 101b), each vessel having a feed side and a brine side, and each side having an inlet port and an outlet port for directing fluid into and out of the pressure vessel. The pressure exchanger system also includes a valve system adapted to direct brine or feed fluid into an out of the pressure vessels at predetermined pressures and an elongation absorber device (50) having a housing element (70) configured for connection to a pressure vessel support and an inner element (60) for connection to a high pressure feed check valve outlet. The inner element is slidable with respect to the housing element in response to length changes of the pressure vessel. Advantageously the sliding movements between the inner element and the housing element of the elongation absorber device allows axial length changes of a pressure vessel with high frequency cycles and avoids mechanical loads and stresses within its piping system and hence avoid
