A vented relief valve is used to unload the pump flow through the relief valve at very minimum pressure setting to avoid over heating your hydraulic system.
Vented Relief Valve
Hydraulic Pump Interchanges
This is the best way to learn how you can interchange any hydraulic pump you have for a better alternative.
Often people need to interchange their hydraulic pumps from existing system to a different pump that can offer better delivery time, pricing, or simply because their old pump hard to find or obsolete.