Before starting a hydraulic power unit, the pressure relief valve should be completely open to allow the pump to start at what pressure?

The pressure relief valve should be completely open before starting the hydraulic power unit to allow the pump to start at the minimum system pressure. This practice helps prevent damage to the pump and the hydraulic system by ensuring that the pump is not subjected to high pressure during startup. When the relief valve is fully open, it allows fluid to bypass back to the reservoir, creating low pressure conditions that enable the pump to start smoothly without encountering resistance from the system. This approach also helps in maintaining the integrity of system components and avoiding stress on the hydraulic system, which can occur if the pump starts at a higher pressure against a closed relief valve.

Choosing the lowest system pressure ensures that the system can efficiently manage fluid flow while reducing the risk of potential cavitation or excessive wear on the pump that could occur if it tries to work against a pressurized system from the outset.