The holding power of a chuck will be a function of the vacuum pressure applied and the surface area of the chuck. We all remember from high school that the area of a circle is
where r is the radius of the circle or chuck. If you apply a vacuum of 15” Hg, this is roughly equivalent to a negative pressure of 7.5 lb/in2 or psi. So, if you have a chuck made from a 2” PVC coupling with a 15” Hg vacuum applied, the holding force would be,