Patent ID: 7481628

Claim:
A diaphragm pump system for pumping a fluid, comprising: a low pressure side pump; a high pressure side pump, the high pressure side pump and the low pressure side pump being connected to each other via a communication passage, the high pressure side pump further including; a housing having an inlet to which the communication passage is connected; a pump chamber defined in the housing; a first diaphragm for sealing the pump chamber; a pressure control chamber defined in the housing adjacent to the pump chamber via the first diaphragm; a second diaphragm for sealing the pressure control chamber; a drive mechanism operable to deform the first and second diaphragms; an introduction passage for introducing into the pressure control chamber a part of the fluid that is discharged from the pump chamber; a pressure regulating valve disposed in the introduction passage for adjusting a pressure in the pressure control chamber to a medium pressure between a suction pressure of the high pressure side pump and a discharge pressure of the high pressure side pump, wherein the pressure regulating valve is only provided with the high pressure side pump; and a branch passage branching from the introduction passage at the pressure regulating valve and connecting to the communication passage, wherein the branch passage drains an extra pressure from the pressure regulating valve to the communication passage when the pressure regulating valve adjusts the pressure of the discharge fluid in the introduction passage.