Fluid exchange devices and related controls, systems, and methods

A method of controlling a pressure exchange device, the method comprising:

• supplying a high-pressure clean fluid to a high-pressure inlet of a valve configured to direct flow of the high-pressure clean fluid to a first chamber;
• transferring a first pressure from the high-pressure clean fluid to a low-pressure dirty fluid through a first piston freely traveling in the first chamber;
• receiving the low-pressure dirty fluid in a second chamber;
• monitoring a location of the first piston and a second piston freely traveling in the second chamber by sensing the first piston and the second piston passing through at least one sensor;
• changing a position of the valve responsive the location of the second piston;
• stopping flow of a low-pressure clean fluid from the second chamber while maintaining the flow of the high-pressure clean fluid into the first chamber for a dwell period;
• continue driving the first piston in the first chamber toward a distal end of the chamber during the dwell period;
• redirecting the flow of the high-pressure clean fluid to the second chamber after the dwell period;
• and
• changing the dwell period responsive the location of the first piston.

A method of controlling a pressure exchange device, the method comprising:

• supplying a high-pressure clean fluid to a high-pressure inlet of a valve configured to direct flow of the high-pressure clean fluid to a first chamber;
• transferring a first pressure from the high-pressure clean fluid to a low-pressure dirty fluid through a first piston freely traveling in the first chamber;
• receiving the low-pressure dirty fluid in a second chamber;
• monitoring a location of the first piston and a second piston freely traveling in the second chamber by sensing the first piston and the second piston passing through at least one sensor;
• changing a position of the valve responsive the location of the second piston;
• stopping flow of a low-pressure clean fluid from the second chamber while maintaining the flow of the high-pressure clean fluid into the first chamber for a dwell period;
• continue driving the first piston in the first chamber toward a distal end of the chamber during the dwell period;
• redirecting the flow of the high-pressure clean fluid to the second chamber after the dwell period;
• monitoring one or more of a velocity or an acceleration of the first piston;
• and
• changing the dwell period responsive to the one or more of the velocity or the acceleration of the first piston.

A system for exchanging pressure between at least two fluid streams comprising:

• a control system;
• and
• at least two pressure exchanging devices, a first pressure exchanging device of the at least two pressure exchanging devices being stacked over a second pressure exchanging device of the at least two pressure exchanging devices, each of the at least two pressure exchanging devices individually comprising:
• a first tank and a first piston independently disposed in the first tank;
• a second tank and a second piston independently disposed in the second tank, the first tank and the second tank being separate from each other and separately formed and defined from other pressure exchange devices, the first tank and the second tank fluidly connected to the other pressure exchange devices by at least one manifold;
• and
• a control valve configured to control movement of the first piston and the second piston solely by directing flow of a high-pressure clean fluid into and a low-pressure clean fluid out of one or more of the first tank and the second tank;
• wherein the first piston and the second piston are configured to exchange pressure from the high-pressure clean fluid to a low-pressure dirty fluid;
• wherein the control system is configured to operate the control valve of each of the at least two pressure exchanging devices to maintain a substantially 180 degree cycle difference between the first piston and the second piston;
• and
• wherein the control system is further configured to operate the control valve of each of the at least two pressure exchanging devices to substantially stop the flow of the low-pressure clean fluid out of the first tank while maintaining the flow of the high-pressure clean fluid into the second tank for a dwell period, the control valve configured to continue driving the second piston toward an end of the second tank during the dwell period.