A valve assembly, the valve assembly comprising: a valve body forming an internal cavity, the valve body further comprising a valve seat part , the valve seat part being located in the internal cavity and dividing the internal cavity of the valve body into an inlet channel and an outlet channel , a communication port being formed in the valve seat part , the communication port connecting the inlet channel and the outlet channel , and a mounting port also being formed in the valve body , the mounting port facing the communication port ; a valve cap , adapted to be mounted at the mounting port ; a valve rod , movably passed through the valve cap ; a valve plug , mounted to one end of the valve rod and able to extend into the internal cavity under the driving action of the valve rod , the valve plug having a neck part extending in the axial direction thereof and an end part extending out transversely from the neck part , wherein, in a closed position, the end part abuts the valve seat part , thereby blocking fluid communication at the communication port , and in an open position, the end part is remote from the communication port , thereby enabling fluid communication; a sealing member , being a flexible sealing member, and configured to at least envelop the valve plug and a side of the valve cap which faces the communication port , so as to isolate the valve cap , the valve rod and the valve plug from the internal cavity of the valve body in a sealed manner; wherein the sealing member has a redundant part ; when the valve plug is at an open position, the redundant part is piled at the neck part of the valve plug ; characterised in that the valve cap has a keyway at a side remote from the communication port so that a tool can be used to screw the valve cap into the mounting port of the valve body . a valve body forming an internal cavity, the valve body further comprising a valve seat part , the valve seat part being located in the internal cavity and dividing the internal cavity of the valve body into an inlet channel and an outlet channel , a communication port being formed in the valve seat part , the communication port connecting the inlet channel and the outlet channel , and a mounting port also being formed in the valve body , the mounting port facing the communication port ; a valve cap , adapted to be mounted at the mounting port ; a valve rod , movably passed through the valve cap ; a valve plug , mounted to one end of the valve rod and able to extend into the internal cavity under the driving action of the valve rod , the valve plug having a neck part extending in the axial direction thereof and an end part extending out transversely from the neck part , wherein, in a closed position, the end part abuts the valve seat part , thereby blocking fluid communication at the communication port , and in an open position, the end part is remote from the communication port , thereby enabling fluid communication; a sealing member , being a flexible sealing member, and configured to at least envelop the valve plug and a side of the valve cap which faces the communication port , so as to isolate the valve cap , the valve rod and the valve plug from the internal cavity of the valve body in a sealed manner; wherein the sealing member has a redundant part ; when the valve plug is at an open position, the redundant part is piled at the neck part of the valve plug ; characterised in that the valve cap has a keyway at a side remote from the communication port so that a tool can be used to screw the valve cap into the mounting port of the valve body . <EOS>