An assembly of a servo pump and a hydraulic motor, wherein: the assembly has a housing which contains the pump and the hydraulic motor; the hydraulic motor has a rotating body which rotates under the motive power of a pressurised motor liquid flow, whereby the hydraulic motor has a high pressure region (P min) which receives the pressurised motor liquid flow, and a low pressure region (P mout) through which the motor liquid flow leaves the hydraulic motor; the pump has a rotating body, whereby the pump has a low pressure region (P pin) which receives servo liquid flow to be pumped by its rotating body, and a high pressure region (P pout) through which pressurised servo liquid flow leaves the pump; each rotating body is mounted on a respective journal (302, 303), each journal being supported on one side of its rotating body by a respective first bearing block and being supported on the opposite side of its rotating body by a respective second bearing block, each bearing block having a running face adjacent to its rotating body and a non-running face distal from its rotating body; the assembly has a mechanical linkage having a coupling at one end to the journal of the motor rotating body and a coupling at an opposite end to the journal of the pump rotating body such that the rotation of the motor rotating body is transferred via the linkage to the pump rotating body; respective static seals seal the non-running faces of the bearing blocks to the housing such that the high pressure region of the hydraulic motor (P min) is sealed from the low pressure region (P mout) of the hydraulic motor, and the high pressure region (P pout) of the pump is sealed from the low pressure region (P pin) of the pump; and a pair of dynamic seals on opposite sides of the pump rotating body seal the journal of the pump rotating body to the housing to seal the low pressure region (P mout) of the hydraulic motor from the low pressure region (P pin) of the pump. the assembly has a housing which contains the pump and the hydraulic motor; the hydraulic motor has a rotating body which rotates under the motive power of a pressurised motor liquid flow, whereby the hydraulic motor has a high pressure region (P min) which receives the pressurised motor liquid flow, and a low pressure region (P mout) through which the motor liquid flow leaves the hydraulic motor; the pump has a rotating body, whereby the pump has a low pressure region (P pin) which receives servo liquid flow to be pumped by its rotating body, and a high pressure region (P pout) through which pressurised servo liquid flow leaves the pump; each rotating body is mounted on a respective journal (302, 303), each journal being supported on one side of its rotating body by a respective first bearing block and being supported on the opposite side of its rotating body by a respective second bearing block, each bearing block having a running face adjacent to its rotating body and a non-running face distal from its rotating body; the assembly has a mechanical linkage having a coupling at one end to the journal of the motor rotating body and a coupling at an opposite end to the journal of the pump rotating body such that the rotation of the motor rotating body is transferred via the linkage to the pump rotating body; respective static seals seal the non-running faces of the bearing blocks to the housing such that the high pressure region of the hydraulic motor (P min) is sealed from the low pressure region (P mout) of the hydraulic motor, and the high pressure region (P pout) of the pump is sealed from the low pressure region (P pin) of the pump; and a pair of dynamic seals on opposite sides of the pump rotating body seal the journal of the pump rotating body to the housing to seal the low pressure region (P mout) of the hydraulic motor from the low pressure region (P pin) of the pump.