A reciprocating downhole pump has a gas separator located at its bottom
end. The separator forms a chamber that is expanded and contracted when
the pump is reciprocated. Expansion and contraction of the chamber occurs
by either the plunger reciprocating in the chamber or a piston coupled to
the plunger reciprocating in the chamber. The chamber has an orifice
therein so that during reciprocation fluid flows in and out of the
orifice. The orifice is sized so as to subject the fluid to a pressure
drop, wherein gas in the fluid is separated from the liquid.