Putting two pumps in a loop.. pros and cons?

[ASFx]

Does anyone have any experience with putting two pumps in a loop to increase flow rate? I was wondering what the pros and cons are.

If the one pump happens to be a bit faster than the other, could it cause problems anywhere in the loop or with the slower pump?

Is there any optimal place to put a 2nd pump in the loop?

Some of you may have seen my setup in this topic here: http://www.ocforums.com/showthread.php?t=523558 and as you can see, i used quite a bit of tubing. I explained my reasons for doing that in the other thread. Although my temps dropped significantly (60-65C to 32-34C), Im now getting curious about just how much faster i would be able to pump the coolant through this loop.

Here are the two pumps that would be in the loop:

Koolance Reservoir/Pump RP-1000BK - http://www.koolance.com/shop/product_info.php?products_id=280
Swiftech MCP355 - http://www.swiftech.com/products/mcp355.asp

[meionm]

That koolance pump is mcp355. So if you add another mcp355 into loop, it will increase head and flow rate.


Addiing another pump will add extra heat to loop. Since you are running miles of tubing extra head and flow might be more beneficial.

[QuietIce]

You'll definitely see a difference in the loop by using two pumps and you've always got a fail-safe that way, kinda' like running RAID1. I'd go series with the MCP355s since their top end is ~2 GPM. That will increase pressure, which in turn will increase flow.

nikhsub1's the guy for info on double pumps - he's been doing them for awhile now and experiments with them more. I prefer to separate my pumps a little in the loop instead of putting them together but it's hard to tell your loop order to make any recommendations ... ;)

[billb]

Does anyone have any experience with putting two pumps in a loop to increase flow rate? I was wondering what the pros and cons are.
Koolance Reservoir/Pump RP-1000BK -
Swiftech MCP355 - Two pumps in series will give an increased flow. Two pumps in parallel will give increased pressure. You can't have both and the whole is less than the sum of the parts, i. e. 0.5 GPM + 1.0 GPM will not be 1.5 GPM.
The same with pressures. The calculations are complicated, but formulas are available.

Why not do something like this if you're looking for extra cooling?
With this setup there is:
No additional restriction on the existing loop
Only the restriction of the rad in the additional loop.
Controllable, you can shut off the second pump anytime extra cooling is not required.

It's an interesting setup for benchmarking. A nice "everyday" radiator with quiet fans and a 3 x 120 rad with 3-200 CFM fans that can be actuated whenever you need that extra cooling.

[johan851]

Two pumps in series will give an increased flow. Two pumps in parallel will give increased pressure.
Isn't it the other way around?

[BobcatDan]

Two pumps in series will give an increased flow. Two pumps in parallel will give increased pressure. You can't have both and the whole is less than the sum of the parts, i. e. 0.5 GPM + 1.0 GPM will not be 1.5 GPM.
The same with pressures. The calculations are complicated, but formulas are available..

True, but the other way round, series increases max head but you are essentially limited to the slowest pumps flow rate, parallel increases flow rate but without much extra head. Though, if it is a highly restrictive loop the extra head will increase flow rate, just not beyond the maximum of the slowest pump. Where parallel setup would increase the flow rate in a lower restriction setup, though I don't think it would double it.

Also, that is a very interesting idea, the secondary loop. If someone had enough extra room that could be very useful, though the heat load would have to be huge to actually use two 3x120 rads! If you could hook the pump and fans up to a water temp controlled relay, that would be sweet too.
Dan

[nikhsub1]

Series increases pressure (theoretically doubles pressure of 1 pump) while parallel increases max UNRESTRICTED flow rate (again theoretically doubles). There would really never be a reason in water cooling computers to run pumps in parallel. Series is the way to go IMO. It really makes little difference where in the loop the pumps are.

[Otter]

I agree with Nikhsub that series is the way to go, but two unmodified DDC3.1/mcp-350's in a low restriction loop might do better in parallel. Most people, of course, would get the 355 or mod the 350's.

If the one pump happens to be a bit faster than the other, could it cause problems anywhere in the loop or with the slower pump?
Yes. I've never tried it, but I've read that if you put dissimilar pumps in series, one is likely to burn out. Placing a block between the pumps is supposed to help with this. With two 355's, though, this wouldn't be a problem. You could put them next to each other.

Is there any optimal place to put a 2nd pump in the loop?
If the pumps are identical, I really don't think it matters. If you put them together right after your res or T you won't have to worry about bubbles increasing wear on the second pump.

[billb]

Isn't it the other way around?Duh! Yes.

[QuietIce]

If the pumps are identical, I really don't think it matters. If you put them together right after your res or T you won't have to worry about bubbles increasing wear on the second pump. I've always used the pump closest to the T-line to bleed the system, then start the other pump.

My personal preference is to separate them since no two pumps are exactly the same ...

[Otter]

True. I don't think the difference would be enough to matter if the pumps were the same version. But come to think of it, there's no guarantee that a new MCP355 is going to be the same as the DDC in the Koolance unit. Laing has made quite a few revisions since they started making 18w DDC's, and only some of them came with new version numbers.

On the side, I'm slightly shocked that Koolance would mess with anything as high quality as a Laing pump. What is that about? Cant they just use some cheap aquarium pump and put up a page about the myth of high head pumps?

[QuietIce]

On the side, I'm slightly shocked that Koolance would mess with anything as high quality as a Laing pump. What is that about? Cant they just use some cheap aquarium pump and put up a page about the myth of high head pumps? LOL!

[IYIENACE]

Adding my second pump/top increased my cpu temp 5c and dropped my gpu temp by 7c.
I'm in the process of swapping out a psu at the moment but after I should have a better idea of how consistent the temps are with mounting blocks.

[IYIENACE]

BTW my loop goes T-line>pump>cpu>pump>gpu>rad

[ASFx]

Thanks for the info. I plan to add the 2nd pump. I just have to look over everything and figure out the best place to put it. I will probably put it between the main loop and rad as billb suggested.