Pressure control device for an inkjet pen

A pressure control device for a reservoir, having a first opening and maintaining a back pressure established therein, comprising:

• a bag, disposed inside the reservoir, communicating with outside the reservoir so as to expand inside the reservoir;
• a pressure plate disposed inside the reservoir and adjacent to the bag so as to move inside the reservoir;
• an isolation member, disposed inside the reservoir in a moveable manner, for sealing the first opening;
• a bias member disposed inside the reservoir and adjacent to the pressure plate, the isolation member, and the reservoir respectively so as to move inside the reservoir, wherein the bias member adjusts the isolation member to seal the first opening based on the movement of the pressure plate;
• and
• an elastic member, disposed inside the reservoir and adjacent to the pressure plate and the bias member respectively, for restraining the expansion of the bag, whereby the bag expands to move the pressure plate when the back pressure inside the reservoir changes, then the pressure plate moves the bias member so that the isolation member separates from the first opening.