Anchorable pack-off assembly

Well pump apparatus for connection to and operation by a reciprocating string of sucker rods which extend downwardly into a well tubing, comprising:

• said tubing constituting an outer pump casing;
• a one-way first valve mounted within said tubing permitting upward fluid flow;
• a hollow member of lesser outer diameter than the inner diameter of said tubing disposed within said tubing and connected to said string of sucker rods for reciprocation;
• lower and upper plungers carried by said hollow member above said first valve in spaced relation and in sealed sliding engagement with said tubing, each of said plungers having a fluid passageway therein in a fluid communication path with said hollow member and said first valve;
• a one-way second valve mounted for reciprocation with said hollow member and operable to provide communication between the fluid communication path and the interior of said tubing above said upper plunger;
• and
• a pack-off assembly anchored in a forced fit in sealed relation within and with respect to the inner surface of said tubing, said pack-off assembly forced into its anchored position by said upper piston and removed from its anchored position by said lower piston in response to a downward force and an upward force, respectively, applied to the sucker rods,
• said pack-off assembly including
• chamber dividing means receiving said hollow member in sealed sliding engagement between said upper and lower plungers to form upper and lower pumping chambers of equal diameter,
• said hollow member including fluid passage means above said pack-off assembly providing communication of the fluid communication path and said upper chamber, whereby during an up stroke fluid is drawn through said first valve into said lower chamber and via said fluid communication path and said fluid passage means into said upper chamber and during a down stroke fluid is expelled via said second valve from said lower chamber via said fluid communication path and from said upper chamber via said fluid passage means and said fluid communication path upwardly through said tubing.