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Pump and Reservoir

You can’t go wrong with a Laing D5, and especially a D5 Vario with a speed control knob on the end. The Alphacool VPP655 is just that and I have no complaints here at all. The D5 is actively cooled by the coolant making it not susceptible to overheating, although it does add ~15-20 W of heat to the coolant as well.

The reservoir/pump top is an Alphacool Repack single D5 pump, dual 5.25″ Bay Station. It comes packaged very well with foam pieces around the item itself which in turn has a thin foam sheet to protect it as well. In terms of accessories, you get a 2.5 mm Allen key and 8 small screws with a 2.5 mm Hex head to help install it. It will take up 2 5.25″ bays so you best make sure your case has those to spare.

The reservoir itself is mostly all plexi with a front face plate that is black to contrast with the clear acrylic, and has markings to keep note of coolant levels. This has the same disadvantages of all D5 bay reservoirs in that the inlet to the pump is at the 50% level mark and so that is the minimum amount of coolant you must have to feed the pump with coolant, and not air. The return line from the loop comes in around 25% and so there is just a quarter volume of fluid available as contingency here. The pump top is built-in, and the volute cut into the plexi itself with the outlet port from the res/pump combo at the top above the return port as seen from the back. No extra ports here, and I would have liked to see some lighting options to view the coolant level in low ambient light. More importantly, there is no vibration dampening on the reservoir and so there may be vibration noises transferred from the pump to the reservoir to your case. There is a dedicated fill port however:

Unscrew the plug from the front and you can pull it out slightly to reveal a hole which can be used to pass coolant through and into the reservoir. While this sounds good in theory, in practice that small hole makes it hard to use. You would be better off buying a fill bottle or syringe to help push coolant through that small hole and not making a mess outside.

Both return and pump inlets have baffles to help with turbulence and shake off air bubbles, but you should still expect to have to bleed air longer than loops with a taller, cylinder style reservoir.

To install the pump, all you have to do is use the provided Allen key, take off the 8 screws holding the pump clamp on the back, push the pump in place with the gasket already present and screw the clamp back on:

No sleeving on the pump cables, as with most rebranded Laing D5 pumps, so keep that in mind.


The Alphacool VPP655 installed in the Bay Station was connected to a very simple loop consisting of it and just tubing and fittings connecting the outlet port to the inlet port directly, and distilled water used for testing. The pump was powered on via the full size MOLEX connector for power and RPM readout was done using an Aquacomputer Aquaero 6 XT. After air was bled, noise measurements were taken 6″ away in an anechoic chamber at 19 dBA ambient noise levels.

The D5 is fairly quiet, even at the ~4800 RPM that it spins at Setting 5. I recommend running the pump at the highest setting that is tolerable noise wise.

To get a better idea of how the pump performs, I assembled the same loop as before except with a Dwyer 490-1 wet-wet manometer with the high pressure and low pressure ports between the inlet and outlet of the pump to measured the pressure drop across it (the loop had a valve to help increase/decrease liquid flow restriction easily) and a King Instruments rotameter helped measure the average flow rate. The pump was fed 12 VDC constantly here. In order to provide context, I did the same with the Topsflow TDC, the XSPC X2O 420 pump which comes as part of res/pump units and also an EK SPC-60 pump. I set the D5 at Setting 5, and 3 (you will soon see why), and the X2O 420 only takes 12 VDC directly from the PSU for a total of 5 P-Q curves including the Topsflo TDC which was also set at 12 V.

Generally speaking, you would like to see a pump have a good balance of pressure head and flow rate. The higher both are, the better of course. The Laing D5 has great max flowrate but at the expense of slightly lower head compared to the Laing DDC. As such the D5 is recommended for a lot of low-medium restriction loops and, being quieter and cooler than the DDC along with proven long term reliability, is one of the most popular pumps in this industry. This is also why it is my standard pump for comparison here and why I am happy to see this pump in the Alphacool kit.

In order to test how good the Alphacool top was, the same P-Q tests were performed except with the same D5 pump with different D5 pump tops:

The Alphacool D5 top in the Repack Bay Station is right up there with other competitors, and does a commendable job throughout.

So overall, both the pump and the pump top are really good and the bay reservoir is a compromise.

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