A pressure regulating valve comprising: a first inlet port configured to be connectable to a high pressure region of an auxiliary fluid circuit; a second inlet port configured to be connectable to a main fluid interface line of a main fluid circuit; an outlet port configured to be connectable to a low pressure region of the auxiliary fluid circuit; and an aperture connecting the first inlet port and the outlet port and defining a fluid path from the high pressure region of the auxiliary fluid circuit to the low pressure region of the auxiliary fluid circuit; a valve spool assembly comprising a valve spool and a valve sleeve arranged to circumscribe the valve spool, wherein the valve spool is configured to be slidably moveable within the valve sleeve between a first position corresponding to a minimum pressure within the main fluid interface line and a second position corresponding to a maximum pressure within the main fluid interface line to change an area of the aperture as a function of fluid pressure within the main fluid interface line; and wherein the valve spool assembly further comprises an annular gap disposed between the valve spool and the valve sleeve, characterised by: the annular gap being configured to be in fluid connection with the second inlet port connected to the main fluid interface line, the valve spool is configured to slide in a first direction from the first position corresponding to the minimum pressure within the main fluid interface line to the second position corresponding to the maximum pressure within the main fluid interface line responsive to an increase in pressure of fluid within the annular gap, and the valve spool is configured to slide in a second direction from the second position corresponding to the maximum pressure within the main fluid interface line to the first position corresponding to the minimum pressure within the main fluid interface line responsive to a decrease in pressure of fluid within the annular gap. a first inlet port configured to be connectable to a high pressure region of an auxiliary fluid circuit; a second inlet port configured to be connectable to a main fluid interface line of a main fluid circuit; an outlet port configured to be connectable to a low pressure region of the auxiliary fluid circuit; and an aperture connecting the first inlet port and the outlet port and defining a fluid path from the high pressure region of the auxiliary fluid circuit to the low pressure region of the auxiliary fluid circuit; a valve spool assembly comprising a valve spool and a valve sleeve arranged to circumscribe the valve spool, wherein the valve spool is configured to be slidably moveable within the valve sleeve between a first position corresponding to a minimum pressure within the main fluid interface line and a second position corresponding to a maximum pressure within the main fluid interface line to change an area of the aperture as a function of fluid pressure within the main fluid interface line; and wherein the valve spool assembly further comprises an annular gap disposed between the valve spool and the valve sleeve, characterised by: the annular gap being configured to be in fluid connection with the second inlet port connected to the main fluid interface line, the valve spool is configured to slide in a first direction from the first position corresponding to the minimum pressure within the main fluid interface line to the second position corresponding to the maximum pressure within the main fluid interface line responsive to an increase in pressure of fluid within the annular gap, and the valve spool is configured to slide in a second direction from the second position corresponding to the maximum pressure within the main fluid interface line to the first position corresponding to the minimum pressure within the main fluid interface line responsive to a decrease in pressure of fluid within the annular gap.