Patent ID: 8166993

Claim:
A ram blowout preventer (BOP) for sealing a well, the ram BOP comprising: a body having first and second conduits, the first conduit being substantially perpendicular to the second conduit; a piston extending through the first conduit and being configured to reciprocate inside the first conduit, the piston having a body portion, a neck portion and a head portion in this order, wherein a thickness of the neck portion along a direction substantially perpendicular to the first and second conduits is smaller than a thickness of the body portion and the head portion along the same direction; a ram block disposed on the piston and configured to move with the piston inside the first conduit to close the second conduit, wherein the ram block has a recess in a back region configured to receive the neck portion and the head portion of the piston such that a gap is formed between the back region of the ram block and the body portion of the piston across a part of the neck region of the piston; and a shim configured to fill the gap between the back region of the ram block and the body portion of the piston.