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.