How many pumps do I need for 20 meters of tube length? Which ones to get?

[Krzych]

Hi,

I am building external water cooling loop, with my PC placed in a different room than than rad/pump. Distance is around 9 meters in one direction, and both the pump on external unit and the PC are elevated by around 65 cm (highest points of the loop), so that gives total of 20 meters.

I've tried to run it today with my single pump, EK Quantum Kinetic TBE D5 PWM, and it went quite miserably since the CPU was reaching 60C in BIOS, so there was almost no flow to it.

Question now is whether a second pump would solve the problem or should get more than one, like of these dual-pump units for example, and if even that will be enough? Does second and third pump placement matter?

I could theoretically also reduce the length to around 12-13 meters by using a different room, but then the pump-res would be around 1 meter lower than now so it would no longer be the highest point of the loop and the water would need to go upwards more than now, not sure if that is better.

Here is the rest of components:

EK Velocity waterblock for CPU
Aquacomputer Kyrographics NEXT for both GPUs
16/10mm soft tubing
MO-RA3 360mm radiator

I am also using Alphacool HF quick release connectors, total of 4

Loop is parallel. I've run it normally before trying to go external so everything is otherwise functional. The pump seemed a bit weak from the start though since there were very obvious changes in the temperature of the components when increasing pump speed and it scaled up to 100% speed, so it seemed like one pump is not enough even without this excessive tube length, not sure if this is normal, this is my first build.

Thanks in advance

[Letgomyleghoe]

you should stop looking for a pc pump and rather get one thats meant to push that much water

[For Science!]

6 minutes ago, Krzych said:

 

I would have actually thought it should be enough. BIOS can be weird with temperatures, and would recommend you to actually check load and idle temperatures in the OS.

[Prodigy_Smit]

As @Letgomyleghoe said, I would look into getting an industrial or aquarium pump build to pump water that far.

[Krzych]

7 minutes ago, For Science! said:

I would have actually thought it should be enough. BIOS can be weird with temperatures, and would recommend you to actually check load and idle temperatures in the OS.

It is really not, it barely pumps any water to GPUs and almost nothing to CPU. The readings are correct, the CPU block was very hot to the touch and temp incresed by like 1C every 5 seconds and that's idle.

[bowrilla]

18 hours ago, Krzych said:

It is really not, it barely pumps any water to GPUs and almost nothing to CPU. The readings are correct, the CPU block was very hot to the touch and temp incresed by like 1C every 5 seconds and that's idle.

I think he meant that BIOS temps are weirdly high for some reason - not wrong but high. This indicates not representing true idle. A D5 pump was meant to be used in house heating systems pumping water up and down stories. Your parallel loop is also not helping.

[Krzych]

I've got a lot of help somewhere else, but so far the situation is that I've ordered dual D5 pump unit (EK-XTOP Revo Dual D5 PWM Serial) for a total of 3 pumps including my current one and I've also found a much better route for the loop, with 14 meters of strait patch and no elevation instead of 20 meters with 65 cm elevation on each side for a total of 1.3m and few 90 degree turns, very gently routed turns with soft tubes by still. Thats 3 times pump power, 70% the length and total elimination of elevation and turns, so it should be ok, hopefully.

[Dango]

Are you talking about 20M lift? On same level, 1m and 100m have no different for pump.

[Krzych]

10 hours ago, Dango said:

Are you talking about 20M lift? On same level, 1m and 100m have no different for pump.

Fortunately not  It was 20 meters total, around 18.3m was flat (on floor level) and then there was around 70 cm of elevation on each end both for PC and external unit, both connected with quick disconnects. There were also two wall corners on the way and I had to go through the wall on one end, so there were some turns. I made very gentle turns with tubes so there were no 90 degree fittings but still. 

 

Now I am going with a completely different route to a different room, 14 meters with only one gentle turn, not three, and everything will be on the same level. I've also done some testing and it seems like adding a third quick disconnect affects performance significantly even in a short in-case-like loop (I've got 10C CPU temp and 5C GPU temp increase by going from 2 to 3 quick disconnects), and there were 4 of these in this long loop so both external unit and PC were detachable. So this time I will make just the PC detachable and leave external unit without QDCs. So the route itself will be like 2 times easier, if not more, I will have 3 pumps instead of one and number of QDCs will be reduced from 4 to 2.

 

It was a pretty epic fail with the first one but guess this is what happens if your first ever custom loop is 20 meters long, with massive rad, 1.45V HEDT CPU and two 380W GPUs.

[AnonymousGuy]

Assuming you didn't do something dumb like run the CPU block in parallel with the GPU blocks....

 

You shouldn't use 3/8"/10mm tubing for long runs.  You should adapt 1/2" or 5/8" to 3/8" at the PC.  Here's some useful info for you showing resistance of various components, resistance of 10' of 1/2" tubing, and what a D5 vario is capable of: https://martinsliquidlab.wordpress.com/pump-planning-guide/comment-page-1/

 

Here is pressure curves of various pumps, in series the curves are additive.  IE the curve multiplies by 2 if you have 2 pumps in series.  PMP-450 is Koolance's branding of a D5 Vario.  The PMP-450S has different electronics for flowing more at 24V but is still a D5 shell.   The PMP-300 is I belive an LT pump and the 400 is the DDC...I could be wrong on those 2:

 

 

However flowrate is pressure...your loop has a fixed amount of resistance (pressure) and the pump type determines the flowrate.  Meaning you can look horizontally and see what your flowrate would be depending on the pump you use.

 

 

I use a PMP-600 @24V with 100ft of 5/8" hose and it moves a ton of water.  I don't have the exact figure but it's probably around 8mH20 based on my estimated flowrate.

 

Three D5 pumps in series is dangerous with a desktop loop because it can develop more pressure than you are prepared for.

 

I need to emphasize this point...with a single D5 pump it doesn't make so much pressure...you can get away without using hose clamps and loose compression fittings.  When you introduce 3 of them in series with a very restrictive loop you can very quickly run into hoses blowing off barbs, blocks with "flaky" orings starting to leak, etc.  I have been here and I have done this...and it was a mess.   The PMP-600 I mentioned earlier is on a separate loop with heat exchanger...my actual PC is running a single D5 pump on the other side of the exchanger.

 

People saying "look at aquarium pumps" are just fully wrong.  You don't need 10 gallons per minute with 20m of head pressure here.