Abstract: A diaphragm pump includes a transfer chamber containing hydraulic fluid and a pumping chamber for fluid to be pumped. A connecting assembly includes a plunger extending to the transfer chamber. A diaphragm connects to the connecting assembly and separates the transfer chamber and the pumping chamber. A pressure protection device mounts to the connecting assembly and is configured to seal against the transfer chamber when pressure differential, including reverse pressure differential, across the diaphragm exceeds a predetermined value. The pressure protection device is intermediate the plunger and the diaphragm and supports the diaphragm when there is excess pressure differential across the diaphragm.