A hydraulic system to control a plurality of drive motors, the system comprising: i) a master unit hydraulic circuit comprising: a master pump; a master control valve assembly having an inlet fluidly connected to the pump and a first outlet fluidly connected to a drain or reservoir; at least one master motor fluidly connected to a second outlet of the master control valve assembly; a pilot valve assembly fluidly connected in a fluid flow direction between the master control valve assembly and the master motor and having a pilot line; a primary slave valve assembly fluidly connected to the pilot line and having an inlet fluidly connected to the pump, a first outlet fluidly connected to the drain or reservoir and a second outlet; at least one primary slave motor fluidly connected to the second outlet of the primary slave valve assembly; a pilot operated primary pressure reducing valve fluidly connected to or forming part of the primary slave valve assembly and acted on by the pilot valve assembly via the pilot line to reduce the pressure at the primary slave motor below the pressure of the master motor; and a master pressure sensor to measure a pressure at the primary slave valve assembly and/or the primary slave motor; ii) at least one slave unit hydraulic circuit comprising: a slave pump; a pressure regulation valve assembly comprising at least one electrically or electronically controlled secondary pressure reducing valve; a secondary slave valve assembly having an inlet fluidly connected to the slave pump via the pressure regulation valve assembly, a first outlet fluidly connected to a drain or reservoir and a second outlet; and at least one secondary slave motor fluidly connected to the second outlet of the secondary slave valve assembly; iii) the pressure regulation valve assembly connected electrically or electronically to the master pressure sensor to provide operational control of the pressure at the secondary slave motor. i) a master unit hydraulic circuit comprising: a master pump; a master control valve assembly having an inlet fluidly connected to the pump and a first outlet fluidly connected to a drain or reservoir; at least one master motor fluidly connected to a second outlet of the master control valve assembly; a pilot valve assembly fluidly connected in a fluid flow direction between the master control valve assembly and the master motor and having a pilot line; a primary slave valve assembly fluidly connected to the pilot line and having an inlet fluidly connected to the pump, a first outlet fluidly connected to the drain or reservoir and a second outlet; at least one primary slave motor fluidly connected to the second outlet of the primary slave valve assembly; a pilot operated primary pressure reducing valve fluidly connected to or forming part of the primary slave valve assembly and acted on by the pilot valve assembly via the pilot line to reduce the pressure at the primary slave motor below the pressure of the master motor; and a master pressure sensor to measure a pressure at the primary slave valve assembly and/or the primary slave motor; a master pump; a master control valve assembly having an inlet fluidly connected to the pump and a first outlet fluidly connected to a drain or reservoir; at least one master motor fluidly connected to a second outlet of the master control valve assembly; a pilot valve assembly fluidly connected in a fluid flow direction between the master control valve assembly and the master motor and having a pilot line; a primary slave valve assembly fluidly connected to the pilot line and having an inlet fluidly connected to the pump, a first outlet fluidly connected to the drain or reservoir and a second outlet; at least one primary slave motor fluidly connected to the second outlet of the primary slave valve assembly; a pilot operated primary pressure reducing valve fluidly connected to or forming part of the primary slave valve assembly and acted on by the pilot valve assembly via the pilot line to reduce the pressure at the primary slave motor below the pressure of the master motor; and a master pressure sensor to measure a pressure at the primary slave valve assembly and/or the primary slave motor; ii) at least one slave unit hydraulic circuit comprising: a slave pump; a pressure regulation valve assembly comprising at least one electrically or electronically controlled secondary pressure reducing valve; a secondary slave valve assembly having an inlet fluidly connected to the slave pump via the pressure regulation valve assembly, a first outlet fluidly connected to a drain or reservoir and a second outlet; and at least one secondary slave motor fluidly connected to the second outlet of the secondary slave valve assembly; a slave pump; a pressure regulation valve assembly comprising at least one electrically or electronically controlled secondary pressure reducing valve; a secondary slave valve assembly having an inlet fluidly connected to the slave pump via the pressure regulation valve assembly, a first outlet fluidly connected to a drain or reservoir and a second outlet; and at least one secondary slave motor fluidly connected to the second outlet of the secondary slave valve assembly; iii) the pressure regulation valve assembly connected electrically or electronically to the master pressure sensor to provide operational control of the pressure at the secondary slave motor.