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W/C pump back pressure?

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Senior Member
Nov 25, 2001
Niagara Falls, Ontario, Canada
Hi guys,

I was just wondering what pumps would handle/if pumps would handle a little to a lot of backpressure without damage. What I am thinking is, that I might like to try a restrictor valve in circuit to tune the flow rate, I am not sure that "all the flow you can get" is going to be the optimum in every situation. (Unless you have the happy accident of matching your block and secondary cooling VERY well)


Oh, an the top of the mornin' to ya, it just turned St Paddy's here, have a good one,

Road Warrior
What you could do is put a T adapter inline before the waterblock and a line looping back to the resevoir. On the loopback line put an adjustable valve. This would give you the ability to control 50% to 100% waterflow to the block.
If it's a magdrive pump like Eheim or Danner, the backpressure shouldn't hurt it, but watch out for overheating. The impeller still turns without any waterflow at all because it isn't in that close of contact to the side walls in the pump chamber. It would be much like covering a blower fan inlet with your hand. The impeller still turns, and probably speeds up, but the lack of flow won't stop it from turning. Some of the larger Danner's even have adjustable flow built into their pump heads.

You can test it simply enough by just using a vice-grip on one of your hoses....a cheap test to check what it does to pump temps (and water temps) before you blow buck$ on valves and stuff.

Have a good'n!

*edit* if the impeller makes a rattling sound, STOP. Some pumps may depend on water to act as a "hydraulic bearing" which would support the impeller somewhat and help cool the core...Rattling noise=BAD.
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Throttling a discharge valve (on a centrifigal) pump will not hurt the pump. Decreasing flow rate by throttling the discharge valve will increase something called "NPSH" (Net Positive Suction Head) at the suction at the suction of the pump. More NPSH is good so from this respect there is no problem. As was stated above, decreasing the flow rate too much will eventually damage the typical (much larger) centrifigal pump. However, I do not know if the amount of heat generated in these tiny pumps will matter. I suspect it will not.

The suggestion above to use a bypass loop to adjust flow rate is an excellent solution and will provide excellent flow control. It is a practice that is frequently used in much larger applications. A bypass loop has a downside because the total flow the pump and motor sees is not really being reduced. The amount of electrical energy the pump uses ends up in the fluid as heat. Since the motor has to do more mechanical work at greater flow rates more heat energy ends up in the fluid. In large systems this does not typically matter that much. In these very tiny systems the pump heat can become a significant percentage of the CPU heat so the total heat load on the system is significantly increased when the flow rate through the pump increases.

In summary, throttling the discharge means less pump heat is put into the system but has some very small risk of damaging the pump if the flow is reduced too much (almost to zero). Using a bypass loop will give better control of the actual flow and not risk damaging the pump but now you also have to remove more pump heat in addition to the CPU heat.

If it was me, I would simply throttle the discharge from the pump. I do not think, but I am not 100% sure, that these pumps/motors are sufficiently powerful to create enough heat (even at shutoff head) to damage them. I bet an email to Eheim would answer this question for sure.
Thanks guys,

I think I might have had a far more awesome idea though. If I go overkill on the pump spec, instead of using just a tpiece as a bypass, I might build an oversized (probably need to be about as big as a coffee mug, the main chamber) water adapted, Ranque Hilsch vortex tube in there with flow control on the "warm" output (that's the bypass), then it might be possible to get your water temp just before the CPU at a degree or two below ambient in a sealed radiator system with no refrigeration or bongs.
Road Warrior