I been testing this (2) small ceramic pumps since yesterday after months of using (2) more powerful Koolance PMP-400 pumps which I think is so overkill for my set up & also very noisy. I also tried using an XSPC X20 200 acrylic pump / reservoir combo (in my search for a much quieter pumps) for about a week but the pump on XSPC X20 is so weak it barely able to move any liquid.
The small ceramic pumps seems to be able to do the job pretty well moving liquids. But it's not what I considered silent (at least from what I read about it). The pumps in series are very noisy. I've used the (2) thicker rubber o rings that comes with the Alphacool bay reservoir that I've used for the pumps. I never have the chance yet to loosen the screws that's holding the pump so hopefully this will solve the problem.
The (2) screws on each pumps are much shorter that the (2) screws that's holding the plexi sealing cap that comes with the reservoir. This is one of the problems that I noticed with this Alphacool set up. If you loosen the screws too much there's just very little of this screws holding the pump on it's thread. Eventually, there's a possibility that the screws will get loose due to pump vibrations with you don't screw it tight.
The small ceramic pumps I think can be modded to have additional 3rd tachometer wire. I think this was first designed to have the 3rd wire in it as there's another small hole where the 3rd tachometer wire comes out in the pump enclosure. I'm tempted to solder a 3rd wire in it but not sure on how to open the pump cover. I might cracked the pump cover so I'll wait for someone to try this first before I'll do this kind of modding.
I think the main problem with this Alphacool set up is not the pump but the reservoir. The reservoir is poorly made. The inlet & outlet ports are too close to the sides of the reservoir though I don't think this is that big of a problem or can be solve as there's really very little space in between each pumps. The pump faceplate is also poorly painted on the back. I tried removing the reservoir faceplate in an attempt to try to paint the back of it but ended up pealing off the paint as the faceplate is not just held with screws but also glued in placed. The Alphacool logo in front of the faceplate is not evenly placed. I tried moving it straight a little bet with my thumb & ended up peeling the logo sticker. This is more of aesthetics problems but if you're into making it look so perfect & neat, this particular reservoir is not for you.
The biggest problems with the reservoir is how they glued the acrylic reservoir in placed as will as the pump volute cut. The acrylic reservoir enclosure are not glued in detail. I saw parts with bubbles in it or even a small gaps. This can be a source of future leaks. I have hard time putting the pump inside the 5.25 inch drive bay of my CM Storm Scout as the back portion of the acrylic cover is glued about 0.1 cm off to the right side hitting the side of the drive bay on a very tight fit.
Improving the pump volute cut & making sure that the impeller doesn't rub against the acrylic reservoir will most probably solve the noise problem. The o ring just doesn't cut it.
Alphacool should look very closely on the quality of built of their product, either aesthetics or performance.