Question about my loop

[bob4933]

I want to clear this up...because there's some stuff in here that's pretty wrong.

Firstly, when your pump is cavitating, that just means it's sucking air, no more. Water is incompressible, so you won't be able to make bubbles out if it without there being air in the loop already...shy of supercavitation at least. This is bad because the pumps that we use for WC are largely based on ceramic bearings which rely on the fluid they are pumping to cool and lubricate the bearing. Run dry, the pump can fail quite quickly.

Secondly, the location of the pump in a closed loop generally won't matter...certainly not in the case of the pumps that we use in any common computer case. You're talking about the pump's head needing to overcome restriction because it's at a high point, but this is incorrect. Any fluid that it fights gravity to move up eventually gets a gravity assist back down, this is the nature of the closed loop.
If you have your res immediately before your pump (which it should be, and in this case is an inherent feature of the res/pump), it does not matter where in the loop your pump/res is located. Air naturally tries to work its way to high points (flow in the loop can move it from these points, it won't just sit at high points), so if you have your pump near a high point and the res is not immediately before it, then you can run into issues of sucking air through the pump...which, as I mentioned earlier, is bad.

Hopefully that clears some stuff up. Feel free to have reasoned discussion on this.

Sorry, but lots of schooling and practical application say other wise. Pumps cavitate due to pressure drops, not just air in the system. If you dont have enough pressure prior to your pump, you can cavitate your pump, regardless if there is air in the system or not. You're implying pumps can't cavitate if the system has no air, which is completely untrue. This is why valves can cavitate as well as pumps. Supercavitation has nothing to do with pumps also.


When I first posted, I wasn't thinking he had an attached reservoir, and his pump was ABOVE the cylinder reservoir he had installed, hence my relative alarm at his setup. With the reservoir attached, that kind of changes things, but pumps still operate most efficiently at the lowest point in the system. Location matters 100%, closed loop or not. Maybe not AS practically in this situation, as it is a relatively small system and he has an attached reservoir, but in general, it always matters to some degree.

Last, but not least, the more pump head you have, the higher your pumps output on a centrifugal pump. This means, more water faster which means a more efficient system.

 

[m0r7if3r]

Sorry, but lots of schooling and practical application say other wise. Pumps cavitate due to pressure drops, not just air in the system. If you dont have enough pressure prior to your pump, you can cavitate your pump, regardless if there is air in the system or not. You're implying pumps can't cavitate if the system has no air, which is completely untrue. This is why valves can cavitate as well as pumps. Supercavitation has nothing to do with pumps also.


When I first posted, I wasn't thinking he had an attached reservoir, and his pump was ABOVE the cylinder reservoir he had installed, hence my relative alarm at his setup. With the reservoir attached, that kind of changes things, but pumps still operate most efficiently at the lowest point in the system. Location matters 100%, closed loop or not. Maybe not AS practically in this situation, as it is a relatively small system and he has an attached reservoir, but in general, it always matters to some degree.

Last, but not least, the more pump head you have, the higher your pumps output on a centrifugal pump. This means, more water faster which means a more efficient system.

Maybe I need to brush up on cavitation...I thought that it was a necessary condition for cavitation that there be air present in the system?

Just so we're clear, there are two reses, one a pump/res. The loop order is res>pump>cpu>res>rad.

Addressing this as an aside, is head not the ability to overcome restriction, while "output", as it were, of the pump is the flow? Which is to say, isn't the head irrelevant in a restrictionless (ideal) setup, and thus only relevant because of the restriction introduced?

Regardless, however, I'm not sure that this really addresses the issues which OP is having. Further, I think that if having a pump in a bay-res caused issues, we'd be seeing a LOT more people with issues, as that type of setup is very common.

I stand by my conclusion that there is air getting trapped in the rad that cannot bleed due to how the radiator is oriented. Given, I am not sure of this, but I think that it's at least a good place to start. Can I presume, since you did not address it, that you agree?

 

[bob4933]

Maybe I need to brush up on cavitation...I thought that it was a necessary condition for cavitation that there be air present in the system?

Just so we're clear, there are two reses, one a pump/res. The loop order is res>pump>cpu>res>rad.

Addressing this as an aside, is head not the ability to overcome restriction, while "output", as it were, of the pump is the flow? Which is to say, isn't the head irrelevant in a restrictionless (ideal) setup, and thus only relevant because of the restriction introduced?

Regardless, however, I'm not sure that this really addresses the issues which OP is having. Further, I think that if having a pump in a bay-res caused issues, we'd be seeing a LOT more people with issues, as that type of setup is very common.

I stand by my conclusion that there is air getting trapped in the rad that cannot bleed due to how the radiator is oriented. Given, I am not sure of this, but I think that it's at least a good place to start. Can I presume, since you did not address it, that you agree?

No, not at all. I dont disagree that air is getting into the system, however, fundamentally, cavitation is when a pump operates below a certain pressure. Whether or not air is in the system or not doesnt matter, that only exacerbates the problem. If you pressurize air above the reservoir, that is actually ideal. We have some water tanks that operate on that principle!

Also, fundamentally, pump head is NOT the "Ability to overcome" it is simply a measure of output. If said output over comes a restriction to flow, terrific! Some systems actually have recirculations installed simply to allow flow in case the pump doesnt overcome said restriction.

In such a small and low pressure system, I know my head is elsewhere, and you are 100% correct about the radiators. As I mentioned before, I was under the impression he simply had a pump ABOVE the reservoir, which yes, will cause problems. I didnt realize he had an attached reservoir. I do recant some of my statements from earlier due to that misinformed judgement, but my thought process is still correct.

I know im applying a far too large principal on this, but its one of those "if its worth doing ,its worth doing right" kinda things for me is all.

 

[m0r7if3r]

No, not at all. I dont disagree that air is getting into the system, however, fundamentally, cavitation is when a pump operates below a certain pressure. Whether or not air is in the system or not doesnt matter, that only exacerbates the problem. If you pressurize air above the reservoir, that is actually ideal. We have some water tanks that operate on that principle!

Also, fundamentally, pump head is NOT the "Ability to overcome" it is simply a measure of output. If said output over comes a restriction to flow, terrific! Some systems actually have recirculations installed simply to allow flow in case the pump doesnt overcome said restriction.

In such a small and low pressure system, I know my head is elsewhere, and you are 100% correct about the radiators. As I mentioned before, I was under the impression he simply had a pump ABOVE the reservoir, which yes, will cause problems. I didnt realize he had an attached reservoir. I do recant some of my statements from earlier due to that misinformed judgement, but my thought process is still correct.

I know im applying a far too large principal on this, but its one of those "if its worth doing ,its worth doing right" kinda things for me is all.

Ah...interesting...having now done my research on cavitation (I did a bit of reading last night and a bit more this morning) I feel like I have a much better grasp on it. It seems like the "bubbles" caused during cavitation do not have air in them, as I had assumed, but rather that they contain water vapor, correct?

Don't pumps operate on a PQ curve, just like fans? How about considering an extreme example comprised of a loop of 0 restriction, a loop of infinite restriction, a pump of infinite flow (but no head), and a pump of infinite head (but no flow). These parts are purely theoretical. If you attached the pump of infinite flow (PF) to the loop of zero restriction (L0), then you would have infinite flow. If you attached the pump of infinite head (PH) to L0, you would have no flow. If you attached PL to the loop of infinite restriction (LI), you would have no flow. If you attached PH to LI, you would still have no flow. Assuming this is correct, then the head is just a means to enable flow, right?

At this point I'm just assuming OP is gone and carrying on an interesting discussion of physics!