(57) A single or double acting reciprocating pump has a plunger (12) constituted as the
rotor of a linear electric motor, the stator being constituted by the pump casing
in which the plunger (12) moves. The plunger (12) can be annular, the casing can then
have a core around which the plunger is received, and rotor and stator windings (17,
15) can then be provided at either or both of inner and outer faces of the plunger
(12). The plunger (12) can extend into a pump end of the pump through a seal (27)
from a driving end in which the motor is located, the driving end being oil-filled.
The pump is suitably embodied for use in a pipe stack in a fluid extraction apparatus.
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