Abstract: A pressure vessel for reducing air entrapment bubbles inherent in lost pattern type casting mould compounds and for increasing the density of the mould material, which in turn has proven to provide a smoother finished surface to the cast material. The pressure vessel consists of separable upper and lower halves held together under loading with an eccentric cam system. The eccentric cam has an overcenter position which causes a greater closing force to be applied to the pressure vessel as pressure is increased within the chamber. Integral to the closing cam is a separate locking cam which operates in unison with the eccentric cam to prevent the eccentric cam's positioning lever arm from being moved while the chamber of the pressure vessel is pressurized.