Noisy Closed Loop...

[reverendmaynard]

Hey guys,

I just finished my closed loop and installed it on the tank on Sunday afternoon. It works well for adding flow, but it is awfully loud and there are occasional bubbles. There must be a leak in the plumbing somewhere (or maybe cavitation?), but I can't seem to find it and would like some ideas on how to diagnose the problem.

The pump is a Quiet One 6000 plumbed with 1.5" pvc. The intake and output connections on the pump are 1" threaded, so I used a 1" threaded to 1.5" slip bushing, screwed on as tight as possible by hand, with a single wrap of teflon tape. The tank is not drilled, so both the intake and outputs are over the back. The intake has a T with a threaded plug at the highest point, for priming. The output side is a "circular" manifold with 8 Ts for outlets, 2 of which are plugged. All plumbing that is not submerged is glued, except for the down pipes that come off the manifold and down into the water on the output side. The pump is located behind the tank, with the bottom of the pump level with the bottom of the tank.

So, if I run the pump with the output-side ball valve wide open, there's a constant sound of air in the pump, and copious microbubbles. Turning the ball valve to half way open quiets it down considerably, with the sound of air in the pump only every second or two, and fairly large bubbles (1mm or so), also every second or two. Occasionally (15min to an hour apart) it'll get a little louder for a few seconds and a stream of microbubbles will come out. Using a hose for a stethoscope-like device, the noise is definitely coming from the impeller chamber of the pump, and I was unable to locate any sounds of leakage any where in the plumbing. There's also a ball valve on the intake side, which I leave wide open, but when I accidently left it closed, there was no flow at all, and no noise, which leads me to believe (perhaps wrongly) that if there's aleak on the input side, it's on the other side of the ball valve from the pump. There is a very tiny leak (just a drop of water that never seems to get big enough to drip off) on the output side, I think from the threaded fitting on the pump, but I don't see how that could get air in the impeller chamber.

Can anyone give me some advice on how to locate the problem and fix it? Could it just be a matter of air trapped in the system that will eventually work itself out? Could I have cavitation?

TIA

 

[Aquaduck]

You've got an air leak on the inlet side. No doubt about it. Check every joint, seal, gasket on the plumbing coming out of the tank up to the pump inlet. I would be very suspicous of the cap on the top of the T. My closed loop was drawing air in through the gasket there. A bead of silicone spread around it stopped the air from getting in and still let me undo the cap. Another thing you may need to do is provide the pump with a larger inlet. I would go to 1.5" pipe and reduce it right near the pump inlet.

 

[reverendmaynard]

I'm already using 1.5" pipe. It's not reduced until the threaded bushing that connects to the pump. I tested the cap by putting a bead of water all the way around it. It didn't change anything, and the water stayed on there for at least an hour.

 

[Pyrojon]

It's possible that you have an air inlet somewhere on the input side but I don't think so, see below.

Your setup sounds fine but you could eliminate the possibility of air getting in through your fill cap by eliminating it. Just plumb from the tank over the top and straight to the pump. Prime it by directing a powerhead at either the input or output side to push water into the plumbing.


The reason I think you may not have air in the system is this, I have the exact same problem as you describe.

I recently setup a closed loop with a blueline 40x pump (1200gph model), with 1.5" on the input and 1" on the output. The pump has 1" input and output. Just like you I have 1.5" all the way to the pump with only a reducer on the threads itself. I have a gate valve on the input side, and it's plumbed through the back of the tank, not over the top.

When I open the gate valve completly I get a horrible cavitation noise in the impeller housing but no air in the system. I can eliminate the noise by closing the valve to about 50%. (Note the valve is on the input side, not the output side.) I still get decent flow but I would rather not have to close the valve at all.


I'm particularly dissapointed to read your story because I just purchased a Quite One 6000 hoping that this would fix my problem. Apparently it's not going to.

 

[reverendmaynard]

I have PM'd Melev to see if he will chime in, hopefully he can help us.

Everything's all glued up, so eliminating the fill cap really isn't an option without reworking the whole thing. I'm confident I have eliminated that as the problem anyway, as I was able to apply a bead of water all the way around the area where the plug threads in and it stayed there and didn't change the behavior of the system at all.

That's really weird that you stop the noise by closing an intake-side valve. I thought cavitation was from inadequate delivery of water to the intake, which you would think would get worse by restricting that side. Maybe we've both overplumbed the intake, actually causing it to be harder for the pump to draw water, rather than easier as we planned (like drinking from a 1.5" diameter straw may be harder than drinking from a .25" straw?). I'm going to try messing with both valves to see if there's an equilibrium point I can reach that will quiet it and allow close to 100% flow. If that doesn't work, I'll have to bust out the silicone and start applying it to every possible seam.

If you haven't opened up that pump yet, you might want to wait 'til I get this resolved so you can return it if necessary.

 

[Pyrojon]

<a href=showthread.php?s=&postid=7637840#post7637840 target=_blank>Originally posted</a> by reverendmaynard


That's really weird that you stop the noise by closing an intake-side valve. I thought cavitation was from inadequate delivery of water to the intake, which you would think would get worse by restricting that side. Maybe we've both overplumbed the intake, actually causing it to be harder for the pump to draw water, rather than easier as we planned (like drinking from a 1.5" diameter straw may be harder than drinking from a .25" straw?). I'm going to try messing with both valves to see if there's an equilibrium point I can reach that will quiet it and allow close to 100% flow. If that doesn't work, I'll have to bust out the silicone and start applying it to every possible seam.

I find it really weird as well that giving the pump more water would cause cavitation, and worse, taking water away eliminates it. That's why I'm thinking that maybe it's not cavitation. I just can't think of anything else that it might be. It sure sounds like cavitation and there are no bubbles coming from my closed loop.

Try leaving your output side fully open and only closing the input side a bit to quiet the noise. If the pump is only designed to have a 1" input you can't be restricting the input till you close that valve to more then 50% and therefore it seems that you shouldn't effect the output flow much till that point. My output seems to be effected when I close the gate valve a bit, but not a whole lot so I may just live with it.

I just received the pump yesterday and I havn't set it up yet but the current pump is still pretty close to 100% when I close my input down by about 50% so I may just plumb this new one in (it's going to be a second pump, not a replacement.) and live with the slight reduction of flow. Maybe I can come up with a way to open those valves at certain times to give a little bit more flow.


Keep me posted on your progress because I'm definatly interested.
Btw, we are not the only two people having this problem, I have seen a couple other threads that are similar, though this is the first I have heard of any pump other then the Blueline (Pan World, etc...) experiencing it.

Jon

 

[melev]

Here's a thought: All new plumbing takes 14 days to slime over, and once this has occured, air bubbles cease being a problem.

You state that your INput side is larger than the pumps intake, which sounds good. What about the strainer inside the tank? Is it restricting the flow too much? Could you remove the strainer temporarily?

Odds are you've tried this, but when I had a noisy pump situation, I'd unplug it for 10 to 15 seconds, then restart it up and it would run silently. Typically the only time I had a noise issue was when the power company staggered the power for a few seconds, which was enough to cause some air to get trapped apparently.

I'm subscribed to this thread, so as you both work on the problem I'll see if I can help.

 

[reverendmaynard]

I thought that the pipe sliming thing might be the source of my airbubbles, as there are air bubbles all over the outsides of the pipes that are in the water. It just makes it harder to tell if I've got a leak or if this is cavitation or something.

Pump has been plugged/unplugged quite a few times, both with rapid stops/restarts and with prolonged off periods (up to 1/2 hour). I've even tried tilting and shaking the pump, both on and off, to see if there's air stuck in a high point or something, though I doubt air can get stuck in the impeller chamber for this long.

Yes, both sides of the plumbing are done with 1.5", downsized only for the 1" threads on the pump. My strainer is 1.5" pvc with 112 1/4" holes drilled in it. I have tried removing it, with no change.

I'm going to try tuning the ball valves a little more tonight. If that doesn't work, I'll try setting it up in my tub with enough water to at least submerge the pump, which will also cover the horizontal run of the intake plumbing. If that stops it, I'll know it's a leak. If not, it still could be a leak in the un-submerged part, but would seem to point more strongly towards cavitation. This will be a PITA, so I'll probably wait at least 'til the weekend for that, to give the pipes more time to slime.

I'll also try to take some pics, in case there's something about the setup that's not right.

Thanks everyone!

 

[reverendmaynard]

Here's a pic of the plumbing attached to the pump, up to the unions.

 

[melev]

It might be that you have 1.5" plumbing on both sides. I think you need 1.5" on the intake and 1" on the output. (I realize you have 1/2" outlets to add some restriction though) This is one of those things that you have to deal with on a case-by-case basis due to the type of pump you've selected.

The bathtub test should help, but you really need to test it with saltwater.

Wait a minute. You have the water basically falling into the pump, and pushing out the side... maybe it would work better if it was entering the pump at a 90 degree angle like mine was on the 29g, and then pushed straight up to the tank again.

 

[reverendmaynard]

No, that's the intake on the front of the pump (running horizontal), output goes up. On the intake, after that union is a ball valve, a 90 going up to the top of the tank, a T with the primer cap going up and the T'd part going over the top of the tank, then a 90 to go back down, into the water. About 4" below the water line is the strainer, which extends down another 6-8".

I can silence the thing completely (I think) by shutting the output ball valve more, but flow starts to get severely impaired, to the point that my Hydor Flos don't rotate.

When you say "due to the type of pump you've selected", what do you mean? The fact that it's magnetic drive rather than direct? What would you recommend for a better pump that I can, hopefully, just screw my existing plumbing onto?

 

[melev]

What I meant by that was that with a Mag pump, you double the threaded outlets when you plumb them. With the Quiet One, that may not be the case. I've never owned that pump, so I don't know. Did the instructions state to do so?

Where the plumbing screws into the intake of the pump, what is the diameter of that part? It could be bottlenecking it enough to cause a problem.

 

[reverendmaynard]

The pump has 1"mpt fittings. I used a 1"fpt to 1.5" bushing there.

I just assumed that doubling it was better than not, and that it was the same type of pump as a mag drive, so I went with that recommendation. Don't know of any mfgrs recommendation. I'll see if I can find something on that.

 

[melev]

Be sure to post what you find out. You don't have the original instructions that came in the box?

 

[reverendmaynard]

They don't mention plumbing at all. The pump came with female threaded fittings with 3/4" hose barbs on them, if that means anything. I may try disconnecting all my intake plumbing and sticking one of those on there with a hose to see what happens, but as in Pyro's case, it seems counterintuitive to restrict the input side to correct this problem.

 

[Pyrojon]

Hi, Wow this thread got busy fast.

Melev,
My plumbing is exactly as you suggest above 1.5" in, 1" out. The input side has a gate valve, and the output side has nothing but a few bends over the top of the tank.

If I open the input gate valve all the way I get noise, if I close it about half way the noise is gone.

I am inputing through a 1.5" bulkhead through the back wall, about 7" up from the bottom of a 24" tall tank, not over the top, the output is over the top.

I have a screen on the input, but it's the standard 1.5" bulkhead screen and it's pretty clean so I don't think it's restricting, certainly not more then the gate valve is restricting.

Everything outside the water is glued and I don't have any bubble problem so I'm 99% sure the noise is not due to air in the pump.

I have turned it off and waited for bubbles to rise out.

It's been setup this way for two or three weeks so it should be pretty well slimy.

My QuietOne 6000 pump came with instructions in 6 different languages, all pretty much useless. I haven't yet setup my quiet one pump for the closed loop, I am having this problem with a blueline pump, the quiet one was purchased to fix this problem.

 

[melev]

I'm looking forward to seeing what results you have with the new pump, Pyrojon.

 

[reverendmaynard]

I have emailed pentair aquatics, the makers of quiet one, about the situation and included a link to this thread. I'll let you guys know their response, if any. I have a bad feeling it'll be "we don't recommend using our pumps in HOT applications" or something like that, but we'll see.

 

[reverendmaynard]

Well, I am pretty convinced my problem is caused by inadequate flow to the pump intake. Partially closing the valve on the intake side just made it worse. I have throttled back the output to the point where it's virtually silent, but I have no idea how much flow I am still getting. Substantially less than at full throttle for sure. I'm guessing around a 1000gph instead of the planned for 1500 or so.

Pyro, your situation is possibly the opposite of mine. You have 17" or so of water pressure pushing the water through your intake pipe, which is possibly faster than the pump requires it. Partially restricting the intake is only bringing it back to essentially 0 pressure. If that's the case, switching to the QO may be the way to go, since it pumps quite a bit more water. Mine, since it goes over the top, has negative pressure that the pump must overcome, which these types of pump really are not equipped for.

I guess I'd have to go to 2" intake plumbing to run the pump full throttle, although I worry that even that wouldn't be 100% effective. My other options would be an overflow (which I would then have to worry about whether it can keep up with the pump) or drilling the tank (a hugely difficult task in a tank that's setup with livestock and is only about 8" away from the wall.)

Does anyone know if there are pumps that are designed for pulling as well as pushing?

I've had no response from Pentair Aquatics yet.

 

[melev]

In a closed loop application, head loss is negligible. While I understand what you are saying, I don't think pulling it over the top is too restrictive since it almost operates like a siphon once it has begun.

I do feel the intake is restricted based on your comments, and hopefully the larger pipe will be the resolution.