Pump assembly

A pump assembly comprising:

• a cylinder having a suction port defined at a lower end thereof;
• a piston configured to ascend and descend inside the cylinder and having an inlet defined at one side thereof;
• a seal cap configured to ascend and descend inside the cylinder, in while in close contact with an inner wall of the cylinder to open and close the inlet;
• a stem coupled to the piston to be ascended and descended together with the piston and having an outlet defined at an upper end thereof;
• a cylinder cap coupled to an upper side of the cylinder to surround the stem;
• a first elastic member disposed between the seal cap and the stem inside the cylinder;
• and
• a second elastic member disposed between the cylinder cap and the stem outside the cylinder,
• wherein the first elastic member is an elastic body having a cylindrical shape with a hollow portion defined therethrough to surround at least one of the piston and the stem, and
• wherein, when the first elastic member is compressed, the first elastic member is configured to maintain a constant diameter at both longitudinal ends thereof and increase an internal diameter of a middle portion of the first elastic member.