First, the liner of the butterfly valve to choose a clean and transparent, not black and yellow. You can observe the PTFE seated butterfly valve seat and valve plate on the fluoroplastic can be seen, because the black and yellow may be secondary fluoroplastic. But it is not absolute, so it is best to choose clean and transparent state, but to distinguish is the valve body color or fluorine plastic itself black situation.
Secondly, fluorine lined butterfly valve on the valve body and the valve body of the connection, whether there is a relative gap. Why leave space? It is because there will be wear and tear in the use of fluorine lined butterfly valve, and internal leakage will occur after a long time, so as long as there is a gap, the connection between the upper valve body and the lower valve body can be tightened and re-sealed.
Finally, the valve shaft and the valve body on the seal and under the seal can be sealed tightly, mainly depends on the sealing material and its form.