RP-402X2 or RP-452X2

Well, I wanted to mount a tank with two pumps in series, would go with a Thermochill 120.4 radiator and a block EK-Supreme HF - Acetal, which is better the best option? RP-RP-402X2 or 452X2, thanks and greetings.

Depends on if you want to use DDCs or D5s. Neither is the wrong choice.

Both are the wrong choice. Neither one bleeds correctly. You will find moderate success with the 452X2 if you use D5 pumps is serial (both set to the same vario rating) as long as you use the acrylic blocker for the top left reservoir. It isnt as bling bling, but the XSPC dual DDC reservoir works much better. If feel you must go with one of the Koolance models, choose the 452X2. D5 pumps are more reliable and run cooler than the DDC platform.

there is also a 401X2 which is only a single bay res rather than a double bay res. from what i hear (i purchased 2 of them, but have not yet installed them) they don't have the bleed issues that the larger versions have.

And the RP-452X2 with a single D5 does it work?

Yep. It works fine as long as you use the the lower (right) reservoir. It is when you try to use two loops or combine pumps in serial that the upper (left) reservoir rears its ugly head and the bleeding problems begin in the latest Version 1.3

Pedropc: IIRC RP-452X2 or RP-402X2 included "blank" insert to close another pump mounting place for those restops to be usable with single D5 or single DDC pump. Not so sure about Koolance's single slot dual DDC though, have to check.

the blank you are referring to is part of the serial kit. it comes with the copper D-tube that links the two pumps.

No, by blank i referred not serial "U" 180deg interconnect but one that can be bolted on empty pump mount place, when only one pump is installed.

ahhh, misunderstood you - my bad :) yea - mine had blanks for where the pump would install that had to be removed (obviously) before the pumps could be installed.