The PC120 - 6 Travel Relief Valve is a critical safety component in the hydraulic system of the PC120 - 6 excavator's travel mechanism. Its primary purpose is to protect the travel motors and associated hydraulic components from over - pressurization during operation. When the hydraulic pressure in the travel circuit exceeds a preset value due to factors such as sudden stops, obstructions, or excessive loads, the relief valve opens to relieve the excess pressure by allowing the hydraulic fluid to flow back to the reservoir or a low - pressure area.