Quiet Liquid Cooled Gaming PC Build Guide

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This is a followup in two parts to the question of pump noise first raised by the screeching noise exhibited by the EK-SBAY DDC 3.2 PWM in dry testing. The first part explores the cause of that noise; the second part presents acoustic measurements for the pump in wet operation, and compares it to the Swiftech MCP655 PWM Pump used in the build guide.


I solved the mystery of that screeching noise. It took 15 mins; should have done it before.

1. Power up the EK-SBAY DDC 3.2 PWM pump/reservoir again to confirm nasty noise
2. Powered down and removed the pump; 4 screws. The backside turned out to be just a press fitted cover which came off with barely any prying. Front has the pump paddle impeller fitted on the motor shaft and an O-ring pressed up against the reservoir.
3. Powered the pump motor up bare and heard no screeching whatsoever. Listened to it w/PWM control over the whole speed range; no audible sign of bearing issues.
4. Put the pump back in the reservoir, tightened screws firmly but gently. Power it back up: Nasty screeching noise is back.
5. With pump still running, I loosened one screw about one turn and the screeching almost disappeared. Tightened screw, screeching is completely back. Loosen screw, screech is way less.
6. Turned all the screws back to completely tight, then backed off about a half turn loose for all the screws: Now there is no screeching at all!

So the screeching is an acoustic resonance in the reservoir that is excited by vibration in the motor. The only question now is whether the level of vibration in this pump motor is higher than normal. If it is normal behavior, absolutely everyone would complain, so it is unlikely. I think the shaft in this pump motor is probably a bit bent — I could see a fair bit of wobble running it bare while holding it in my hand.

Finally, having examined the electric motor & the pump attached to the shaft, I can't see any reason why the pump would be at risk for damage if run without water. It's just an electric motor with a specialized impeller. Ditto all the pumps used in watercooling, assuming the basic design is the same.

Later, on the same day...

Prompted by more forum comments, I took the pump off again and took another, closer look, and I now understand why running the pump at full speed for long periods could damage the bearing.

The pump, removed from the housing, without the cover over the coil and magnet assembly. The blue portion is the impeller. It wobbles because it is on a unipivot ceramic ball bearing. Magnetic power keeps it in place.

When it is running normally, the metallic cavity in which the impeller sits is immersed in liquid. This includes the bearing, which is lubricated and cooled by the flowing liquid. I could not see any evidence of damage on the ceramic ball but the plastic portion in the impeller that the ball fits into may have been damaged; it is difficult to see clearly.

POSTSCRIPT TWO - 27 Jan 2015:

EK-SBAY DDC 3.2 PWM vs XSPC Reservoir + Swiftech MCP655 PWM Pump

It took a while, but the extra compression fittings and tubing need to test the EK-SBAY DDC 3.2 PWM reservoir/pump in realistic conditions finally came in yesterday. This morning, I spent a couple of hours setting up a simple loop with a new 240mm radiator, filling the loop with water, and running the EK-SBAY DDC 3.2 PWM reservoir/pump.

As I suspected, there was no untoward bearing damage that could be discerned by listening. It pumped the water without issue.

So let's get it out there now: To say I have egg on my face is not enough; I'm also eating crow and humble pie. My sincere apologies to EK, VisionTek and/or Laing for any negative effects of my original report on the acoustics of this pump.

Not only is the EK-SBAY DDC 3.2 PWM much quieter than I first reported, when working in a liquid loop, it is probably quieter than the XSPC Reservoir + Swiftech MCP655 PWM pump. The margin very small, but it seems to be there.

The reported PWM control range of the Laing DDC 3.2 PWM is as reported earlier. RPM actually doesn't change when set manually between 100% and 55% speed on SpeedFan. Between 55% and 20% was the effective speed range, with quite linear steps for each 5% change. Sitting atop a soft piece of foam to damp vibrations, the sound pressure levels measured were quite low.


Compare this with the measured SPL obtained for the Swiftech MCP655 PWM Pump in XSPC Reservoir used for the PC built here. At every speed, the DDC 3.2 PWM measured 2~3 dBA lower.

Swiftech MCP655 PWM Pump in XSPC Reservoir

Now keep in mind that the MCP655 PWM Pump was measured while running DRY, though it had no trace of the resonance that marked the EK-SBAY DDC 3.2 PWM, and as far as I can recall, its sonic character did not change when liquid was coursing through it. The RPM reported for the Swiftech may not be quite accurate either; it was taken from Martin's review because the RPM could not be read from my sample. Still, let's not discount the possibility that running wet, it might measure lower than the 18 [email protected] recorded dry. A true side-by-side acoustic test of the two pumps will have to wait till both can be isolated from any other noise sources.

Suffice it to say that...

1) The EK-SBAY DDC 3.2 PWM in normal wet operation is probably a touch quieter than the Swiftech MCP655 PWM Pump in XSPC Reservoir. In the vast majority of applications, however, fan noise is likely to be higher, and thus the small difference between these pumps would be insignificant.

2) Ignoring any differences in pump performance (ie, pressure, velocity, etc) the two pumps are likely to be equally proficient in cooling SPCR's first liquid cooled gaming PC.

3) Both of these pumps should be used with mechanical decoupling if low noise operation is a must. This probably applies to all water pumps currently available for PC cooling.

My thanks again to VisionTek, EK and FrozenCPU for generously supplying the various parts for this postscript.

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