A locking gas equalizer is provided for use with a subsurface pump for lifting fluids having a high gas content. A mechanical lifting piston and rod are slidably mounted beneath the check valve in the traveling pump assembly. When the pump reaches the bottom of its down stroke the piston raises the rod and unseats the check valve. As the pump cycle reverses at the top of the stroke, the inertia of the piston also causes the rod to be raised for unseating the check valve and allowing a small amount of fluid to drop into the pump chamber. Thus, gas pressure within the pump chamber volumes is positively equalized to prevent gas lock up of the pumping action. A hexagonal alignment slider maintains alignment of the lifting piston to prevent hangup of the piston in a stroke through pump. The hexagon and a locking slot in the piston also prevent relative rotation of the equalizer assembly components to enable the pump sucker rod to be rotated for removal from the pump assembly in tubing pumps requiring on and off tool. The downhole disassembly permits the gas equalizer assembly to be used with large bore pumps for increased pumping volume.
