Back-pressure valve and actuation system

A back-pressure valve comprising:

• a case through which fluid passes and in which a first fluid chamber and a second fluid chamber are formed;
• a piston slidably accommodated within the case so as to partition the first fluid chamber and the second fluid chamber;
• an elastic member for urging the piston in a sliding direction of the piston;
• and
• a communication device for allowing the first fluid chamber to communicate with the second fluid chamber when a fluid pressure in the first fluid chamber reaches a first predetermined value,
• wherein the piston has a check valve for preventing a passage of the fluid from the first fluid chamber to the second fluid chamber and a relief valve for allowing the first fluid chamber to communicate with the second fluid chamber when the fluid pressure in the first fluid chamber reaches a second predetermined valued which is larger than the first predetermined value, and
• the communication device has the check valve and a valve-opening member adapted to be brought into contact with the check valve so as to open the check valve when the piston is located at a predetermined position.