This may be dumb question or idea. I have a dual voltage controller 7V & 12V would setting up a pump like that be any good Thinking same theroy as fans 7V setting for internet and low power consumption and kick it to 12V for max cooling.

Yes, most pumps will operate within a range of voltages. The D4 pump will go down as low as 6V or so if I remember. You shouldn't have to worry about it for your DDC pump though, should be quieter than a mouse.

Won't hurt to try it out. Just remove the power connectors from everything, plug the pump in, and jumper the green wire on the 20/24 pin connector to ground. If it starts up every time, then it's safe.

The new D5 pump has a voltage adjustment on the back of it, and it has a better driving waveform than the D4 pump. Shouldn't be a problem at all, as long as the controller can survive the current draw. Motors are generally constant-power machines, so grab the wattage rating off the pump and use that instead of guessing at lower voltages.

I'm thinking about the MCP650 317GPH that I have on the shelf for the SLI rig I'm building. The modded MCP350 is silent and its in my other rig.

the dual voltage controller
Each switch is rated to a spec of 8W of power
http://www.frozencpu.com/bus-11.html

MCP650
Nominal voltage: 12 V DC
Operating voltage range: 6 to 14 VDC
Nominal power (@ 12 V): 24 W
Nominal current (@ 12 V): 2 amps

Looks like you'll need to use 3 in parallel, and switch them only when the machine is off. If the machine is on when you switch them all at once, there is a high risk of shorting things if the switches do not trip at the exact same time. The pump only uses about 18W when it's going, but that 24W figure would be for startup when the current is higher (rated higher as a safety measure).

If I were you, I'd look at a 3-pole switch that can pass 3-4 amps at 12Vdc. Grab a pass-through molex adapter from a fan, and put the ground and 5V lines to the switch inputs, and your new ground to the molex is the centre pin. Not very hard, it's cheap and safe. You can put that switch anywhere too. I can draw up a diagram too if you want, I'm too tired to do it now.

I would just go for another modded MCP350. It should have plenty of head and GPM for even a SLI rig. That is a lot of amps to bleed off and they can be inconsistant starting at lower volts.