Hydraulic pumping unit with a variable speed triplex pump

In combination with a well-fluid hydraulic pumping unit of the type wherein a prime mover drives an above-ground pump to supply a flow of pressurized fluid, wherein at least some of said pressurized fluid is used as power fluid for a downhole hydraulically actuated pump, which downhole pump returns fluid to the surface wherein at least some of said return fluid is introduced as cyclone flow into the input of a cyclone separator, and wherein a portion of said cyclone flow exits the cyclone overflow as cleaned fluid and is available for use as power fluid, and the remainder of said cyclone flow exits the cyclone underflow and is sent to a flowline, the improvement which comprises:

• a. speed control means connected to said prime mover for controllably varying the speed at which said prime mover drives said above-ground pump;
• b. a cyclone feed pump having an inlet and an outlet, wherein said outlet is connected to said cyclone inlet and wherein said feed pump inlet is connected to receive said return fluid, and
• c. a flowback line connected from said cyclone overflow to said cyclone feed pump inlet, whereby the speed of the above-ground pump can be changed without adversely affecting the cleaning by the cyclone.