cavitation?

[NaCl_H2O]

Ok experts, here is a challenge! On my new setup I have MAG7s being used for my closed loops. The inlet comes from the tank at about 12" from the water surface (The tank is 29" tall), the pump sits on a shelf about 18" from the water surface, and the pump outlet runs over the top of the tank. The inlet PVC diameter from the tank is 1", reducing down to 1/2" for the pump inlet size. Pump outlet is also 1/2". Actually, I have two MAG7s connected to the 1" outlet from the tank, but have them on a timer so I can run only one at a time.

When I first started the closed loops, I had horrible "Micro Bubbles", which have improved somewhat. Not sure if this is due entirely to only running one pump at a time, or pump "Break in", or some minor plumbing changes I made.

Currently, the micro bubbles only occur when the pump starts, for about 1-2 seconds, but that's enough microbubbles to last until the next pump cycle starts :(

I am asuming the bubbles are coming from cavitation of the impellers. The MAG5s on my other tank (same setup) are not creating micro bubbles.

A fluids engineer told me that cavitation is caused because ... "the inlet of the pump has dropped below the vapor pressure of the fluid at its operating temperature. Generally one increases the pump inlet pressure by adding fluid head, like putting the pump at the bottom of the tank or in a well that's deeper than the tank" OK ... :?

Ideas I am kicking around include the following - please give me your thoughts on any or all of these"

1) Major re-plumbing job to drop the pumps lower and increase inlet head pressure as the fluids guy recommended (Definately not a desirable option!)
2) Buy different/better pumps - actually, I am not getting the flow (GPH) I expected from the MAG7s - I have some MAG12s for another purpose and think they are far superior to the MAG5/7 style pumps. Or can someone suggest another/better external pump with a 1/2" inlet/Outlet that may not be as prone to cavitate?
3) Buy a wavemaker with "Soft Start" - would thix fix the cavitation problem?
4) Keep the lights off so I can't see the microbubbles :-D

BTW - I really don't think I have any "air leaks" in the plumbing

As always, thanks for any advice you can offer!

[NaCl_H2O]

Pump cycles are currently set at 30mins. I did leave out one detail - I am using modular pipe (segmented bendable stuff) at the end of the returns, some of which is out of the water. But even if that was "leaking air", I would expect constant microbubbles, not just during pump startup?

[matt]

I bet it's the pumps and/or the possible leaking of air into the circuit through the loc-line. Also, I'm not sure if you have a true closed loop if you have two pumps plumbed to the same circuit, with one not on at a given time. I'm trying to imagine what happens to the water in the line of the pump that's off. Does some of it get drawn towards the pump that kicks on, as the flow in that line creates some sort of suction in the line of the idle pump? I'd have to see a drawing, and even then I probably wouldn't know. What happens when you turn both pumps on at the same time?

But, forgetting about that stuff for now, in general mag pumps are not built well, and with the constant on-off you'll probably have some problems. Why don't you get one big reliable pump with 1" in/out and oscellate it between the two returns? The pan world non-pressure 1200gph sounds perfect for this. BTW, mags are notorious leakers, and if you have a drain to the pump located 12" below the water surface and one of those pumps springs a leak you're looking at a MAJOR disaster.

[NaCl_H2O]

Matt, thanks for the info! Ok, so I have a semi-closed loop ;) I thought about that too, but there doesn't appear to be any suction from the other side/pump, probably due to the height of the returns and plumbing.

Now back to "leaky" MAGs!!!! I am not at all pleased with the MAG5/7s I bought, but the MAG12 seems to be a much better built pump - have you also experienced problems with the MAG12 and above models?

For a "Switching Device", would a SCWD have any chance of working at a reasonable frequency at 1200GPH? Or is the Ocensmotions more of what you were thinking about?

[RobertG]

I would consider the squid on a mag 12, it is not the best pump. However I ran one for years with no issues. I currently have a mag24 running & have the same issues. It seems to surge for some reason. Take the pump & submerge it. Doing this will eliminate the thought the bubbles are coming from a leak on the pump. Tim Marvin has a mag12 on a squid currently. With no problems.

Do you have check valves on these lines? If not I would get some quick, you could have a big mess one day coming home. Unless you have lots of room for water storage when power drops.

I am taking the mag 24 off & adding Dolphin 4700, hopefully this will do away with the bubbles for me.

Good Luck!

[::pete::]

OceansMotions Squirt instead of the SCWD.

http://www.oceansmotions.com/nano1.jpg

.... more plumbing :D

[Bigreefer]

If you are paying that much for a Squirt, why noy just go for a Tunze 6100?

[RobertG]

If you are paying that much for a Squirt, why noy just go for a Tunze 6100?

I agree, the tunze is great! the 6100's move 3200GPH.

[matt]

I think the price difference is pretty significant. But, if you add up the cost of the nice pump and the oceansmotion it might approach the tunze. The oceanmotion is an oscellator, though, which means you get excellent water movement characteristics. Buying a couple of tunzes with a controller to vary the flow is very expensive. The other thing is that a "real" pump like an iwaki or equal plus the oceansmotions will probably last much longer than the tunze devices. At least they sure look to be built much better than the tunze stuff.

[NaCl_H2O]

Ok, y'all have me moving towards spending more money, again! ... does this ever end :-D Guess I am now paying for trying to shave a little original project cost, will I ever learn!

Trying to figure the right combination of pumps, etc. to get the flow rate I "Really" want.

Is anybody using the OcenaMotions Squirt?

How worried do I need to be about exceding it's 1000-1300 GPH "Lock Up" rating? On my 215, If I use a single pump, the PanWorld 100PXX (1270GPH) is probably the minimum needed for the closed loop.

Is www.oceansmotions the only source to buy their units?

I see another trip to HomeDepot's PVC aisle in my future ...

[::pete::]

Is www.oceansmotions the only source to buy their units?

That is the only place to buy OM. Wkopplin has an 8way and you might want to look into that or a 4 way.

8 way has 8 outputs .... :-D

[TAXMAN]

Ok. I have worked in the Balance feild for many years and have worked on a lot of water pump systems. It sounds like your Impeller is cavitating at start up. " Moving faster than the water can move " Which WILL cause the Micro bubbles that is caused by water being turned into a vapor which is Oxygen. Once the water flow is up to speed with the impeller, the bubbles stop.
You can try to lower the pump into the deepest part of the tank which will put more Inlet pressure due to the debth and may help it but I doubt it. You really arent going to get much of a pressure change in less than a foot of distance. Try removing the inlet pipes and then start it to see what happens. It may solve the probelm or make it a little better. If you restrict the output, it may just make it worse. As stated above, I have some MJ1200's that due the same thing from time to time when the filter gets dirty and restricts the input flow.

[NaCl_H2O]

OK, I bit the bullet ($$) today and ordered new stuff to rework my closed loops.

I'm not going to get the huge flow rate (30X+) some others have reported, but I already have a Hot Tub I can use outside ;) ;)

Ordered two PanWorld 100PXX pumps (1270 GPH) for the 215, two PW 40PX (480 GPH) for the 140, and a PW 30PX (258 GPH) for the FOWLR. Four OW Squirts for the 215 & 140, and a SCWD for the FOWLR. With the Sump return, High end (215/SPS) should be 20X-30X, 140/Softies should be around 20X, and FOWLR around 15X.

Anybody want to buy some slightly used MAG5 and MAG7 pumps :-D

[::pete::]

possibly ... what are you looking to get for them

[NaCl_H2O]

possibly ... what are you looking to get for them

I'll probably use one or two elsewhere, but have 4 MAG7s and four MAG5s. Paid $57.95 & $51.95 - I'll let them go for $35 & $30 each?

It will be a week or so until I take them out & replace.

[matt]

I think you'll be really happy you did this once the sticker shock wears off. The pan world pumps are very well made, and I bet the oceans motions thing is too. Remember, this stuff is pushing alot of water around 24/7, and reliability is everything.

Smile!

[NaCl_H2O]

I think you'll be really happy you did this once the sticker shock wears off. The pan world pumps are very well made, and I bet the oceans motions thing is too. Remember, this stuff is pushing alot of water around 24/7, and reliability is everything.

Smile!

Everything else I did on my new system has been high quality, this was one area I tried to save a little money, and I am going to pay twice! Once again I have learned - DO IT RIGHT THE FIRST TIME!

I have a PW 200PXX (1750 GPH) as my sump return pump, and love it - great product! I am sure the others will be just as impressive.

BTW - I spoke w/Paul regading the OM Squirt - great guy, and very helpful. He really cares about his products & customers.