A pressure-controlling device (10) includes a pump (21), a connection pipe (30), a first valve (41), and a second valve (42). The pump (21) has an inlet port (211) and an outlet port (212). The connection pipe (30) has a first end in communication with the outlet port (212), and a second end in communication with the inlet port (211) and that has a first space (31) that contains the first end, a second space (32) that contains the second end, and a third space (33) that is located between the first space (31) and the second space (32).

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.

A pressure-controlling device (10) includes a pump (21), a connection pipe (30), a first valve (41), and a second valve (42). The pump (21) has an inlet port (211) and an outlet port (212). The connection pipe (30) has a first end in communication with the outlet port (212), and a second end in communication with the inlet port (211) and that has a first space (31) that contains the first end, a second space (32) that contains the second end, and a third space (33) that is located between the first space (31) and the second space (32).

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.