Elastic member and pump assembly comprising same

A pump assembly comprising:

• an elastic member having:
• a protrusion portion on an outer side of the elastic member,
• a recessed portion on an inner side of the elastic member, wherein a pair of the protrusion portion and the recessed portion are repeatedly formed in a longitudinal direction,
• an outer groove defined in the protrusion portion along an outer circumference of the elastic member, and
• an inner groove defined in the recessed portion along an inner circumference of the elastic member, wherein the outer groove and the inner groove are configured to deform during an elastic compression, and wherein a rigidity of the protrusion portion is greater than a rigidity of the recessed portion;
• a cylinder of which a first portion and a second portion are open and in which a hollow is formed;
• a seal cap disposed on an inner wall of the cylinder;
• a supporting part being positioned underneath the elastic member to provide support;
• a piston rod having an inlet which is configured to open or close by the seal cap formed at a lower end of the piston rod and a passage connected to the inlet extending to an upper end of the piston rod;
• and
• a stem coupled to the piston rod to move upward or downward with the piston rod,
• wherein the elastic member is provided between the stem and the supporting part and provides an elastic force from the supporting part toward the stem.