ELBOW 0009077 - Caterpillar

Upstroking means that the pump is increasing the displacement (output). Upstroking occurs when the signal oil pressure increases due to an increased load. The highest signal oil pressure from the control valves flows through line (2) and the oil fills chamber (4). The force of signal oil pressure plus the force of springs (3) now move margin spool (1) to the left. The spool movement blocks the flow of pump oil to large actuator piston (12). The spool movement also opens the passages to the large actuator piston to case drain (11). The combined force of the actuator spring and of