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General Liquid/Water Cooling Discussion For discussion about Full Cooling System kits, or general cooling topics. Keep specific cooling items like pumps, radiators, etc... in their specific forums.

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Unread 10-02-2002, 07:52 AM   #26
gmat
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Quote:
Originally posted by myv65
Are you certain it's cavitation? It could also be simple vibration of the pump. Two things you can do to verify.
(snip)
Good points, i had already verified though
It's mounted on 1cm of noise-killing material, and decoupled with neoprene foam layers from the case which itself is fully padded in noise-insulating material... No vibration, sir, i'm positive about that, sir.
Ah and it is the noise it makes in the sink when i cut the flow manually.

Quote:

Increasing pressure) You can put a water column open to atmosphere [...] (snip)
I like my closed, stealth black cube. Besides i'm in closed loop, and i dont want water to get in contact with ambient air (bacterias etc...). Oh and lugging the cube to LANs is a must, as well.

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If you really want to get funky,
Now that pleases me Let's see:

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[...] Be warned, though, that overpressurizing an accumulator will cause fittings to blow.
I like that ! Sounds *fun* to me. (quite like this: "-Do not cross the streams. -Why? -It would be Bad.")
More serioulsy. I suppose that one places the accumulator just before the pump inlet, right ?
Where could i find this kind of gizmo ? Pet shop ? (i imagine the stares i'll get when i'll ask for this kind of thing. Oh well, such is life)
I have a small airtrap. Is it a problem ? (yes it has tight o-rings on both ends. i'm more concerned with the residual air pocket inside the trap)

Quote:

Decreasing velocity) You can open the suction line as you have proposed.
So you say it would work. Porting the "suction cup" would not be too hard, considering it's only made of plastic.
The outcome would be a decrease in pump efficiency, i suppose, as the design is based on incoming water velocity and tight impeller housing design. What i would not want is losing efficiency and keeping that cavitation noise...
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Unread 10-02-2002, 04:17 PM   #27
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"Don't cross the streams." Now that was a classic scene.

Anyway, where you locate an accumulator does not matter. It has no effect on system flow rate or relative pressure drop. All it does is allow you to artificially increase the absolute pressure everywhere in the system.

I've never considered one for water cooling. We always used them on our hydraulic power skids as a means to absorb pressure spikes and to keep supply pressure fairly constant under varying loads when using pressure compensated pumps. It's common to have big ones on homes with wells and in the States you can buy them at any home improvement store. What you'd be seeking is considerably smaller. I am unaware of a ready-made one, so you'd probably have to make your own.

What you would need is a short length of PVC pipe with solvent-welded end caps. At the bottom, you'd have to make a connection to a T in your tubing. Since no flow goes through the line, the size is irrelevant. On the top end cap, you'd need a normal tire air valve (Schrader - spelling???). Alternatively, you could have a second port connected to a pressure gauge.

You fill the pipe partially with water, then pressurize the air space to a few psi (1/3 to 1/2 bar). That's all there is to it. As temperatures change, the pressure will also change a little. This should be no concern so long as the system remains air tight. At some point, you'll likely need to "pump it up" to maintain your cavitation-free operation. Just don't run much higher than you need to as this raises the pressure on all your fittings.

[edit start]
So long as you already have an airtrap, you could simply pressurize it. It would still function as before, but also gives you ready-to-use accumulator if you add a tire valve. Good luck.
[edit end]

Last edited by myv65; 10-02-2002 at 05:46 PM.
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Unread 10-03-2002, 07:38 AM   #28
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I "port" all the pumps I buy ,paying special attention to the suction side, some were pretty good already and didn't show much improvement, others gained up to 25% extra head (though that was an extreme case)
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Unread 10-03-2002, 08:22 AM   #29
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Quote:
Originally posted by Volenti
I "port" all the pumps I buy ,paying special attention to the suction side, some were pretty good already and didn't show much improvement, others gained up to 25% extra head (though that was an extreme case)
I might ask you for some tips on that...

M2-MDQ-SC has a similar inlet, with 3 ports. I don't think much could be done to it, as it holds the ceramic shaft, but I guess I could hack around it, a little bit.

I'll take a pic and get back to you.
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Unread 10-03-2002, 08:30 AM   #30
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As long as the topic of cavitation came up, it's worth noting that you can have cavitation only within the pump or in the tubing leading up to the pump. If it's the former, then porting, raising overall pressure, or reducing flow rate will all help. If it's the latter, you'll be able to see a fine stream of bubbles in the tubing leading to the pump suction. In this instance, porting the pump will have no effect. Lowering flow rate or raising overall system pressure are the only options. I've never seen a case where a closed system had cavitation occuring ahead of the pump but see it frequently in open systems that have odd suction resistances.
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Unread 10-03-2002, 04:36 PM   #31
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speaking of cavitation, this helped me to understand things a little bit more...
http://www.mcnallyinstitute.com/01-html/1-3.html
http://www.mcnallyinstitute.com/index.html
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Unread 11-05-2002, 01:00 PM   #32
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Pfew! It took me an hour to track this thread!

Here are some pics of my pump housing:
Attached Images
File Type: jpg pump housing pics 1 of 2.jpg (51.9 KB, 63 views)
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Unread 11-05-2002, 01:01 PM   #33
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And more:
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Unread 11-05-2002, 01:07 PM   #34
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And more (attached, this time!)
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File Type: jpg pump housing pics 2 of 2.jpg (50.4 KB, 59 views)
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Unread 11-05-2002, 01:10 PM   #35
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So what do You think Volenti? Can I, should I mod this?

I'm thinking about temporarily gluing a plate on top of the impeller (with a hole in it!). This would prevent the water from recirculating within the pump.
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Unread 11-05-2002, 03:46 PM   #36
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BigBen:

Personally, I wouldnt mod that. Looks great as it is. Unless you want the pump to be self-priming?
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Unread 11-05-2002, 05:50 PM   #37
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Yes it looks good. Does it cavitate (under heavy charge = COMPLETE watercooling circuit in closed loop) ? If so you could consider porting it.
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Unread 11-05-2002, 06:09 PM   #38
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There is an air issue, but I'm not sure where it's from yet, because I've only tested with thin-walled 1/2 vinyl tubing, which promptly collapsed.

So I picked up 3/4 braided.

I also didn't get any hose clamps yet.

Now all I have to do is convert the rest of the stuff to 3/4
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Unread 11-05-2002, 08:54 PM   #39
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Ahh, very interesting, nice to see the impeller design of a fixed rotation pump.

It doesn't need any "modding" as such, if you wanted to do something you could round the edges slightly on the output (from the inside of the impeller chamber, and mabie look at the intake, which from the pics looks to be a little restrictive, but it's difficult to tell for sure.

looks like it'll pump like a champ.
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Unread 11-06-2002, 02:04 AM   #40
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WoW!, nice!, what pump is that BB?...
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Unread 11-06-2002, 09:06 AM   #41
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It's a Little Giant 2-MDQ-SC. ~550 gph @ 0 head, shut-off at 14.4 feet.

I've figured out that its most efficient at 250 gph, at which point the head is about 11 feet.

Picked it up at a flea market for $40...

I checked out the little giant website, and this is the closest I found to it: 2-MD-SC specs

I might try to swap some parts for the model 3, if I can get them cheap.
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