A valve assembly comprising a valve body and a mono-material plunger , wherein: the valve body has a primary opening and a secondary opening , wherein the primary opening and the secondary opening are axially spaced apart; the plunger comprises: a primary seal portion configured to selectively occlude the primary opening ; and a secondary seal portion configured to selectively occlude the secondary opening ; and wherein the plunger comprises the following operational positions with respect to the valve body: a transit seal position in which: the primary seal portion of the plunger is in contact with the valve body in order to occlude the primary opening ; and a fluid flow position in which: the primary seal portion of the plunger is spaced apart from the valve body such that fluid can flow through the primary opening ; the secondary seal portion of the plunger is spaced apart from the valve body such that fluid can flow through the secondary opening ; and the plunger is maintained in the fluid flow position by an external force and a force caused by a pressure differential across the valve assembly . the valve body has a primary opening and a secondary opening , wherein the primary opening and the secondary opening are axially spaced apart; the plunger comprises: a primary seal portion configured to selectively occlude the primary opening ; and a secondary seal portion configured to selectively occlude the secondary opening ; and a primary seal portion configured to selectively occlude the primary opening ; and a secondary seal portion configured to selectively occlude the secondary opening ; and wherein the plunger comprises the following operational positions with respect to the valve body: a transit seal position in which: the primary seal portion of the plunger is in contact with the valve body in order to occlude the primary opening ; and a fluid flow position in which: the primary seal portion of the plunger is spaced apart from the valve body such that fluid can flow through the primary opening ; the secondary seal portion of the plunger is spaced apart from the valve body such that fluid can flow through the secondary opening ; and the plunger is maintained in the fluid flow position by an external force and a force caused by a pressure differential across the valve assembly . a transit seal position in which: the primary seal portion of the plunger is in contact with the valve body in order to occlude the primary opening ; and a fluid flow position in which: the primary seal portion of the plunger is spaced apart from the valve body such that fluid can flow through the primary opening ; the secondary seal portion of the plunger is spaced apart from the valve body such that fluid can flow through the secondary opening ; and the plunger is maintained in the fluid flow position by an external force and a force caused by a pressure differential across the valve assembly . the primary seal portion of the plunger is spaced apart from the valve body such that fluid can flow through the primary opening ; the secondary seal portion of the plunger is spaced apart from the valve body such that fluid can flow through the secondary opening ; and the plunger is maintained in the fluid flow position by an external force and a force caused by a pressure differential across the valve assembly . <EOS>