Is mixed (DDC+D5) pumps in series a bad idea?

After reading https://martinsliquidlab.wordpress.com/2011/04/26/pump-setup-series-vs-parallel/3/ (ddc and d5 was used for test) I assume it is ok to use different pumps in series? I mainly would use it for redundancy (even with my 2x420,3x360 and 1x200mm rads, one gpu and cpu block (everything is known to have low restriction though) D5 at 3 is enough). Right now I have three pumps – dc12-400, ddc by thermaltake and D5 and am keeping the first two to test new rads/flush loop etc. but would love to use two in series in my loop so in case d5 fails I have some redundancy. And should I put pumps before or after the D5? I assume it should make *no* difference (and ddc is likely going be in the middle of my long loop)?

Honestly I suspect where you place them and whether or not they are series or parallel really won't matter. I'd personally place them in parallel, so they balance themselves, but again I doubt it will.make a huge difference

I wouldn't mix them:

- The pumps will have different flow rates and control for optimum noise. Whilst I haven't used a D5, I can say that the DDC works for me around 2000-2500 rpm. At maximum (approx. 4000rpm) it vibrates my desk and generates a whine.
- Having two similar pumps means exactly the same speed curves which would be far more simple.

Run them in series to combine their pumping pressure. It's no different than batteries in a electrical circuit where the waterblocks and radiators act as resistors.

Thank you, will do it in series. Totally rebuilding my loop right now and changing (which incidentally involves quite a bit of cutting) my fractal R3 case to accomodate all of my rads (it gonna look hideous, believe me – fitting 200mm rad as bottom intake and drain point of my loop, 3x360mm for side intake 2x420 as top exhouse/external intake + 240 for intake. Wife does not have to like it as it will stand in balcony ).

Off-topic: love moving out of city to countryside, dust is pretty much non-existent so there is no need to have dust filters.