System for pumping an abrasive or corrosive fluid

A system for pumping an abrasive or corrosive fluid, which system comprises:

• pressure-raising means, for raising a pressure in a non-abrasive and non-corrosive liquid, and
• pressure transfer means, for transferring said pressure to the abrasive or corrosive fluid, wherein the pressure raising means comprises:
• at least one variable-delivery pump means,
• two intermediate cylinders each having
• two oppositely disposed end regions,
• a floating piston disposed in each intermediate cylinder and movable between the respective end regions,
• a change-over valve assembly connected to one of the said end regions of each intermediate cylinder and having means for placing that one end region alternately in communication with the pump means or with a drain, the other of said end regions of each cylinder being in communication with the transfer means, whereby when the said one end region of said intermediate cylinder is in communication with the pump means the respective floating piston executes a forward stroke in which it is driven towards the said other of the end regions,
• return means for driving each floating piston towards the said one end of the respective intermediate cylinder when the said one end communicates with the drain,
• control means for changing-over the state of the change-over valve assembly, the control means being adapted to cause the said pistons to reciprocate out of phase with each other with each of the pistons beginning its forward stroke before the other piston completes its forward stroke, and
• sensors provided on the intermediate cylinders for actuation by the presence of the respective floating pistons at positions adjacent the sensors, the sensors being operatively connected to the control means to actuate the control means, and wherein the pressure transfer means comprises:
• a respective pressure transfer vessel for each intermediate cylinder, each pressure transfer vessel having:
• a first port connected to the said other of the end regions of the respective intermediate cylinder and
• a second port connected by a first non-return valve to an outlet for pressurized abrasive or corrosive fluid and connected by a second non-return valve to an inlet for receiving further abrasive or corrosive fluid for pressurization.