A well tool 1, wherein said central disc portion is domed and is cooperatively positioned within said housing with {HEAD ~ its concave surface} facing {TAIL ~ said forward end} of said mandrel to better withstand pressure forces acting on the convex surface of said central disc portion 
facing
A well tool 1 , wherein said central disc portion is domed and is cooperatively positioned within said housing with { HEAD ~ its concave surface } facing { TAIL ~ said forward end } of said mandrel to better withstand pressure forces acting on the convex surface of said central disc portion
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH