An energy recovery apparatus comprising: a rotor configured to move a duct containing low pressure fluid into alignment with a high pressure fluid source port for replacement of low pressure fluid in the duct with high pressure fluid, the rotor further configured to move the duct while containing high pressure fluid into alignment with a low pressure port in an end cover for release of the high pressure fluid within the duct to low pressure; and the end cover comprising: the low pressure port (310, 320); a high pressure seal surface (316, 326) adjacent the low pressure port (310, 320), the high pressure seal surface (316, 326) configured to maintain high pressure on fluid in the duct during movement of the duct into alignment with the low pressure port; a groove (414, 514) disposed on an outer surface of the end cover and forming a transition between the high pressure seal surface (316, 326) and the low pressure port (310, 320), the groove (414, 514) configured to bleed off pressure from fluid in the duct as the rotor moves the duct over the groove (414, 514) into alignment with the low pressure port (310, 320), wherein the groove (414, 514) of the end cover forms an impeller surface (418, 518) configured to impart rotational force to the rotor; and a low pressure seal surface adjacent the high pressure fluid source port, the low pressure seal surface configured to maintain low pressure on fluid in the duct during movement of the duct into alignment with the high pressure fluid source port, characterized in that the apparatus further comprises a further groove forming a transition between the low pressure seal surface and the high pressure fluid source port, the further groove configured to bleed high pressure fluid into the duct from the high pressure fluid source port as the rotor moves the duct over the further groove into alignment with the high pressure fluid source port. a rotor configured to move a duct containing low pressure fluid into alignment with a high pressure fluid source port for replacement of low pressure fluid in the duct with high pressure fluid, the rotor further configured to move the duct while containing high pressure fluid into alignment with a low pressure port in an end cover for release of the high pressure fluid within the duct to low pressure; and the end cover comprising: the low pressure port (310, 320); a high pressure seal surface (316, 326) adjacent the low pressure port (310, 320), the high pressure seal surface (316, 326) configured to maintain high pressure on fluid in the duct during movement of the duct into alignment with the low pressure port; a groove (414, 514) disposed on an outer surface of the end cover and forming a transition between the high pressure seal surface (316, 326) and the low pressure port (310, 320), the groove (414, 514) configured to bleed off pressure from fluid in the duct as the rotor moves the duct over the groove (414, 514) into alignment with the low pressure port (310, 320), wherein the groove (414, 514) of the end cover forms an impeller surface (418, 518) configured to impart rotational force to the rotor; and a low pressure seal surface adjacent the high pressure fluid source port, the low pressure seal surface configured to maintain low pressure on fluid in the duct during movement of the duct into alignment with the high pressure fluid source port, the low pressure port (310, 320); a high pressure seal surface (316, 326) adjacent the low pressure port (310, 320), the high pressure seal surface (316, 326) configured to maintain high pressure on fluid in the duct during movement of the duct into alignment with the low pressure port; a groove (414, 514) disposed on an outer surface of the end cover and forming a transition between the high pressure seal surface (316, 326) and the low pressure port (310, 320), the groove (414, 514) configured to bleed off pressure from fluid in the duct as the rotor moves the duct over the groove (414, 514) into alignment with the low pressure port (310, 320), wherein the groove (414, 514) of the end cover forms an impeller surface (418, 518) configured to impart rotational force to the rotor; and a low pressure seal surface adjacent the high pressure fluid source port, the low pressure seal surface configured to maintain low pressure on fluid in the duct during movement of the duct into alignment with the high pressure fluid source port, characterized in that the apparatus further comprises a further groove forming a transition between the low pressure seal surface and the high pressure fluid source port, the further groove configured to bleed high pressure fluid into the duct from the high pressure fluid source port as the rotor moves the duct over the further groove into alignment with the high pressure fluid source port.