Apparatus for and method of pumping output fluids such as abrasive liquids

An apparatus for pumping an output fluid, especially a particle-laden liquid material comprising:

• (a) an output pump including an output piston and its own pumping chamber for pumping a discrete amount of said output fluid from its pumping chamber by causing said output piston to move through a complete forward stroke;
• (b) a drive pump including a drive piston and its own pumping chamber connected with said output pump through a common chamber containing intermediate drive fluid, said drive pump having means for moving said drive piston through its own complete forward stroke in order to pressurize said drive fluid within said common chamber in a way which causes said output piston to move in the forward direction of its stroke;
• and
• (c) said drive pump and output pump being configured such that the forward stroke of said drive piston defines a greater swept volume than the forward stroke of said output piston for causing the output piston to move through its entire forward stroke before said drive piston completes its forward stroke, whereby as said drive piston moves through its entire forward stroke, a predetermined amount of said drive fluid must be removed from said common chamber;
• (d) means for removing said predetermined amount of drive fluid from said common chamber each time said drive piston moves through its entire forward stroke;
• and
• (e) means for adding the same amount of new drive fluid to said common chamber before the next successive forward stroke of said drive piston, whereby the new fluid can be provided at a colder temperature than the drive fluid already in the one common chamber in order to lower the temperature of all of the drive fluid within the common chamber;
• (f) said output pump including means for causing said output piston to move through a complete rearward stroke after having moved through a complete forward stroke by refilling the pumping chamber of said output pump with the same discrete amount of new output fluid that was previously pumped out of said last-mentioned chamber, and said drive pump including means for causing said drive piston to move through a complete rearward stroke after having moved through a complete forward stroke, said last-mentioned means being synchronized with said means for causing said output piston to move through its rearward stroke such that the two pistons start their rearward strokes at the same time and such that said output piston completes its rearward stroke before said drive piston completes its rearward stroke, whereby during the time said drive piston is completing its rearward stroke after said output piston has stopped, a negative pressure is created in said common chamber.