Abstract: The present invention is directed to a downhole pump assembly having a housing, a standing valve located near the lower end of the housing, a plunger disposed in the chamber of the housing below the upper and lower internal shoulders thereof and adapted for reciprocating movement through at least a portion of the chamber of the housing, and a traveling valve located in the plunger. A pull rod has one end connected to the plunger and an opposite end connected to a sucker rod string to affect reciprocating movement of the plunger. A sliding valve is positioned in a chamber of the housing between an upper internal shoulder and an internal shoulder.