A hydraulic motor assembly for an aerial refueling system, comprising: a supply conduit for conveying hydraulic fluid from an aircraft hydraulic system, a return conduit for conveying hydraulic fluid to the aircraft hydraulic system, and a pump conduit for conveying hydraulic fluid between the supply conduit and the return conduit; a valve comprising an inlet coupled to the supply conduit, and an outlet coupled to the pump conduit; a variable displacement motor-pump comprising a first port coupled to the return conduit, a second port coupled to the pump conduit, and a spline shaft for being coupled to a hose reel of an aerial refueling system, wherein the variable displacement motor-pump operates in a pump mode to convey hydraulic fluid from the first port to the second port when the hose reel rotates in a trail direction, and wherein the variable displacement motor-pump operates in a motor mode to convey hydraulic fluid from the second port to the first port when the hose reel rotates in a retract direction; and a pump-motor relief valve comprising: a control chamber divided into an actuator chamber and a regulation chamber by a spool having a first face and a second face, the actuator chamber being in fluid communication with an inlet conduit and housing a bias spring configured to exert a load on the first face, the regulation chamber being in fluid communication with the pump conduit; and a mixing chamber being in fluid communication with the supply conduit, the pump conduit, and the return conduit and housing a portion of the spool, the spool separating the mixing chamber from the control chamber, wherein the spool is configured to control mixing of hydraulic fluid flowing from the supply conduit and the pump conduit through the mixing chamber into the return conduit when the variable displacement motor-pump operates in the pump mode, and wherein the spool is configured to prevent hydraulic fluid from flowing through the mixing chamber into the return conduit when the variable displacement motor-pump operates in the motor mode. a supply conduit for conveying hydraulic fluid from an aircraft hydraulic system, a return conduit for conveying hydraulic fluid to the aircraft hydraulic system, and a pump conduit for conveying hydraulic fluid between the supply conduit and the return conduit; a valve comprising an inlet coupled to the supply conduit, and an outlet coupled to the pump conduit; a variable displacement motor-pump comprising a first port coupled to the return conduit, a second port coupled to the pump conduit, and a spline shaft for being coupled to a hose reel of an aerial refueling system, wherein the variable displacement motor-pump operates in a pump mode to convey hydraulic fluid from the first port to the second port when the hose reel rotates in a trail direction, and wherein the variable displacement motor-pump operates in a motor mode to convey hydraulic fluid from the second port to the first port when the hose reel rotates in a retract direction; and a pump-motor relief valve comprising: a control chamber divided into an actuator chamber and a regulation chamber by a spool having a first face and a second face, the actuator chamber being in fluid communication with an inlet conduit and housing a bias spring configured to exert a load on the first face, the regulation chamber being in fluid communication with the pump conduit; and a mixing chamber being in fluid communication with the supply conduit, the pump conduit, and the return conduit and housing a portion of the spool, the spool separating the mixing chamber from the control chamber, wherein the spool is configured to control mixing of hydraulic fluid flowing from the supply conduit and the pump conduit through the mixing chamber into the return conduit when the variable displacement motor-pump operates in the pump mode, and wherein the spool is configured to prevent hydraulic fluid from flowing through the mixing chamber into the return conduit when the variable displacement motor-pump operates in the motor mode. a control chamber divided into an actuator chamber and a regulation chamber by a spool having a first face and a second face, the actuator chamber being in fluid communication with an inlet conduit and housing a bias spring configured to exert a load on the first face, the regulation chamber being in fluid communication with the pump conduit; and a mixing chamber being in fluid communication with the supply conduit, the pump conduit, and the return conduit and housing a portion of the spool, the spool separating the mixing chamber from the control chamber, wherein the spool is configured to control mixing of hydraulic fluid flowing from the supply conduit and the pump conduit through the mixing chamber into the return conduit when the variable displacement motor-pump operates in the pump mode, and wherein the spool is configured to prevent hydraulic fluid from flowing through the mixing chamber into the return conduit when the variable displacement motor-pump operates in the motor mode.