What are the three sealing parts of the instrument valve

What are the three sealing parts of the instrument valve
There are three sealing parts of the instrument valve: the contact between the opening and closing parts and the two sealing surfaces of the valve seat; Instrument valve packing and valve stem and stuffing box with the place; The joint between valve body and valve cover. The sealing performance of instrument valve refers to the ability of the sealing parts of instrument valve to prevent medium leakage, which is an important technical performance index of instrument valve. One of the previous leakage is called internal leakage, which is usually said to be not closed tightly, it will affect the ability of instrument pipe valve to cut off the medium.
For block valves, internal leakage is not allowed. Instrument valve is a kind of pipeline accessory. It is used to change the channel section and medium flow direction, and control the medium flow.