Pump Performance Testing

The pump used in the CORSAIR Hydro XD7 is the Xylem D5, which has a history of reliable and good performance backing it. But as with every product we receive, it was put through the full test suite. To test a D5 pump, I typically use a reference D5 top from XSPC (XSPC D5 bay reservoir) and the pump separately after disassembly. This is to decouple the pump's performance from the pump top's performance as part of the reservoir, which is tested separately. However, this time, disassembly was not easy, so I went with the Hydro XD7 as-is. Given this is a PWM pump, the first thing to test is its RPM response. To do so, I used the pump in a simple loop of reservoir-in to reservoir-out, with PWM control and RPM monitoring from an Aqua Computer aquaero 6 XT I also compared to the CORSAIR Commander Pro for consistency.


There have been a few years of inconsistency when it comes to PWM control with the Xylem D5 pump, especially as a result of it not conforming with Intel PWM spec 1.3. A few manufacturers took it upon themselves to work around it, and a few others claimed to be working with Xylem to resolve this issue once and for all. This latest iteration thankfully addresses all the previous issues, and we see a nice linear pump speed response with the PWM signal. As generally expected with PWM duty cycle control in the PC DIY sector, there is an increased range of control at the lower end and a full-speed operation when no PWM signal is provided relative to the older D5 PWM pumps. The rated RPM for this pump is 4800 RPM with a ~20%–100% PWM duty cycle, which the measured numbers match very well.

In order to see how the pump performs, I used it in the same loop as before, but with a Dwyer 490-1 wet-wet manometer to measure pump head in PSI and a King rotameter to measure average flow rate in gallons per minute (GPM). This P-Q curve for a pump provides extremely useful information as it shows the average flow rate in a loop when any flow restriction is added from blocks and radiators, under others. To produce an ideal but realistic data set, the P-Q curves below are thus for the pumps in a closed loop with minimal flow restriction.


Be sure to click on the thumbnail twice to be taken to a higher resolution image for a better look at the various entry points. I have included other pumps developed within the few last years, including the Xylem DDC at full throttle in the CORSAIR Hydro XD3. A lot of the more budget-oriented pumps introduced recently aim to match the Xylem D5 Vario in Position #3, which corresponds to the D5 PWM at 70% PWM duty cycle. As such, I have included that setting as well, in addition to 100% PWM. The Alphacool VPP755 is a newer "D5-replacement" sold by Alphacool with a different design but a similar housing as the Xylem D5, and it outperforms the D5 PWM pump in the CORSAIR Hydro XD7 with the XSPC top ever so slightly while having a considerably less favorable history of operating reliably. The rest of the lot are hovering around the lower end with only the XSPC X2O 420 in the XSPC Ion and Topsflo TDC doing better, but those pumps might as well be EOL given their lack of availability in the PC DIY space in 2022.