Watercooling, 2 RADS???

[Random Nonsense]

Or get really silly and go for an inner/outer loops system! outer loop cools a battery of TECS which cool the inner loop water, which cools the waterblock, which cools the TEC on the CPU which makes it so cold the silicon shatters!

[JFettig]

3 passes is way too many, way too much flow restriction unless you have a huge pump, 2 passes mite not be a good idea, unless your blocks are really restrictive, im gonna run 2 passes soon because my block is so restrictive(60gph) that its putting stress on the pump.... so im gonna run my nb or gpu block as 1/4tubing and 3/8 to cpu...

[Random Nonsense]

3 passes actually has less resistance than one or two, so the pump wont be having to work as hard and flow will increase, yes it will probably be slower through each pass, but with a beefy pump that doesnt really matter

[Kaitain]

If you're worried about dropping the flow velocity too much, just reduce the pipe diameter. Computer people use too much pipe anyway

If you're going for any sort of multi-pass system, you'll need some sort of flow control (pin or gate valve) on each pass inlet, otherwise you'll find all the water rushing through the pass of least resistance. Be annoying if that happens to be the Northbridge, leaving you with a toasty CPU.

3 passes will have less resistance than 2, because you've only got one major item on each pass, rather than 2 or 3.

You'll get some pressure drop due to the valves, and some due to the manifolds, waterblocks and bends in the pipe - the pressure loss due to these should be equalled or exceeded by your pump's outlet head pressure. Look here to find out how to calculate this... Bends