Help! Return Pump Problem!

[cemyth]

Sorry in advance for this long post but I have a problem that I just can't seem to fix and I have pulled most my hair out over. :headwally:

My mag 12 return pump no matter what I do to increase flow keeps getting cavitation. The only way I can stop the cavitation is to close a ball valve about 13" above the pump half way to create backpressure. The only problem with this is it hinders the flow to just about 330 GPH in the DT. (I figured this out by how fast it filled a 1 gallon container.) I would like to be more at 5x the tank volume or 500 GPH. I original started with a mag 9.5 but that was even less flow and more cavitation. When I tried the mag 12 it was better flow and less cavitation. Should I go with a mag 18?

This is my setup right now. (See Image Figure 2) My sump chambers are: (Skimmer---Return---Fuge). My return pump is "œT" to feed the fuge chamber and (2) TLF reactors. (See Image Figure 1) The flow in the fuge chamber is only about 150 GPH. Should this be more? I have tried it at 300 GPH but the pump had more cavitation, it slowed the flow to the DT and it overall seemed like too much flow in the fuge.

I know that cavitation is created by more output than input from the pump but how do you stop that in a submersible? I have tried to fill the sump all the way to the top with water and that seemed to do nothing. My thought was it would create more pressure on the pump. Right now the pump is in 10 1/2" of water.

I have tried 3 different pipe diameters starting with 3/4" and working my way up to the recommended 1 1/2" diameter. The only difference from the others is the 1 1/2" piping is reduced right at the end to a 1" bulkhead that is drilled into the DT.


As of now I have about 330 GPH returning to the DT, about 100-150 GPH in the fuge and 50-100 GPH on each reactor. Will this work or am I missing or doing something wrong?

 

[seapug]

seems to me the problem isn't with your return pump or plumbing, the problem is with your drains. Can you show or explain your drains from the display?

 

[cemyth]

Sure can.
My drains are really simple. I am using a glass-holes 1500GPH overflow with two pipe drains 1 1/2". They both just go right into the skimmer chamber with a 7" filter sock.

http://www.glass-holes.com/1500-gph-Overlfow-Box-Complete-Kit-gh1500kit.htm?categoryId=-1

 

[cemyth]

I don't know if these will help but here are a few other images.

View attachment 190232

 

[seapug]

Are the drains burping and surging? The reason I ask is once the circulation loop is started, water will drain from the display at the exact same rate it is being pumped into the tank-- unless something is impeding the flow of water through the drains. If the drains are burping and surging and the water level in the display is fluctuating, you have some sort of airlock occurring in the drain plumbing.

 

[cemyth]

Wow! I do have burping and surging sounds coming from the overflow. Thought that was loud but normal. I don’t notice any fluctuation in the water level in the display. What is going on there and how do I fix it?

 

[seapug]

That's the likely source of your problem. It's caused by a cycle of pressure buildup and release in your drains from an insufficient air/water mixture in the drain plumbing.
Short of reconfiguring to a full siphon Herbie/Bean Animal style drain, it's usually fixed by a combination of letting more air into the drain and angling the drain outlets at the surface of the water in the sump so air and water can freely exit. It takes some finessing, but you can usually fix the problem with some experimentation.

Start by pulling the vinyl tubes out of the drain bulkheads shown in the photo above. That will allow more air to enter the drain and sometimes stops the surging. If this does stop the surging, cut the vinyl tubes much shorter and insert them so they don't extend deep into the PVC fitting. That will usually solve the surging problem in the drain. If the problem returns after putting the vinyl tube back in or removing the tube does not solve the problem, drill multiple small (1/8") holes in the fitting near the existing tube until the surging stops. Do this while the tank is running and you'll know when you've hit the "sweet spot". This will "open" the drain and allow more air to enter the plumbing to prevent the partial siphoning, yet still keep the drain relatively quiet.


Once that problem is solved you still may have a lot of splashing and burping in the sump if your drains are a straight vertical drop to the sump. To fix that problem, start by adding an angled outlet at the end of the drain pipe that extends just under the surface of the water in the sump. This will allow water and air to exit the drain without having to build up enough pressure to push the water out of a submerged vertical drain. If your drain outlets are hard PVC, make sure they don't extend more than an inch or so under the surface then slip a 45 degree elbow over the end of the pipe. If you are using flexible hose, you can make something like the picture below. The slight angle created by the elbow fitting allows water and air to exit without a pressure buildup in the hose. Don't laugh, it actually solved the problem on my tank:

 

[cemyth]

I will give these solutions a try when I get home tonight. It has been frustrating trying to figure this out and all along I had no idea it was the drain causing the problem. Hopefully this will stop the pump from cavitation and get a little more flow. If I have any problems I will let you know. Thank you very much!

 

[MarkGP]

From your picture, the skimmer compartment in the sump is 10.5" high. Where is the water level when your pump is running. Does the level go down when you open up the ball valve more to let more flow into the display? If so you might just need to add more water.

 

[cemyth]

From your picture, the skimmer compartment in the sump is 10.5" high. Where is the water level when your pump is running. Does the level go down when you open up the ball valve more to let more flow into the display? If so you might just need to add more water.

Mark"¦When I open the valve all the way up the water level does go down. I have tried adding more water when doing this but with the same results. (Pump cavitation)
The skimmer and return chambers have the same amount of water in them. This only changes when there is evaporation and it only affects the return chamber.

Unfortunately I have experimented with opening the valve all the way and adding water but with no change.

Hopefully the solutions seapug suggested will work.

 

[MarkGP]

Have you tried adding water until the cavitation stops? I run that same gl*******s kit on my 125 and I don't get any surging or noise and I have a bigger return pump.

 

[cemyth]

Have you tried adding water until the cavitation stops? I run that same gl*******s kit on my 125 and I don't get any surging or noise and I have a bigger return pump.

That I have. Filled the sump to the top and still cavitation.

 

[seapug]

I will give these solutions a try when I get home tonight. It has been frustrating trying to figure this out and all along I had no idea it was the drain causing the problem. Hopefully this will stop the pump from cavitation and get a little more flow. If I have any problems I will let you know. Thank you very much!

Sure! Hope it does the trick!

 

[jwilson]

Sorry but I'm not getting this - fixing drains will do nothing to solve cavitation.

If your dt isn't overflowing, then messing with the drains will only help solve the drain noise problem.

Pardon this question but are you sure the pump is cavitating? What is it that you are identifying as cavitation...bubbles in the return outlet flow?
Is it possibly just pumping water and bubbles that are already in the sump?
Is it possible that the pump has not run long enough and is pumping some air trapped in it before being immersed and turned on?
I doubt it's that you don't have enough NPSH (net positive suction head),i.e water pressure putting water into the pump, Unless you're creating a swirl that is drawing air into it from the surface above, (also not likely if you have 10" of water above it!) the only thing I can think of that could cause actual cavitation is that the inlet to the pump is too close to a wall/baffle and that is not allowing enough water flow into the pump.

 

[evsalty]

That I have. Filled the sump to the top and still cavitation.

This may be a stupid question but you did this while the pump was running correct?

I ask becasue if you did this and the pump still pumped out more water then it took in then where did the rest of the water go? If your tank can handle that much water then it sounds like it still needed more in the system to prevent this. If the drains themselves could not handle that much flow then you would have overflowed the DT. WHich makes me think even more that you filled it first then turned the pump on.

How high up is your overflow?

 

[cemyth]

Sorry but I'm not getting this - fixing drains will do nothing to solve cavitation.

If your dt isn't overflowing, then messing with the drains will only help solve the drain noise problem.

Pardon this question but are you sure the pump is cavitating? What is it that you are identifying as cavitation...bubbles in the return outlet flow?
Is it possibly just pumping water and bubbles that are already in the sump?
Is it possible that the pump has not run long enough and is pumping some air trapped in it before being immersed and turned on?
I doubt it's that you don't have enough NPSH (net positive suction head),i.e water pressure putting water into the pump, Unless you're creating a swirl that is drawing air into it from the surface above, (also not likely if you have 10" of water above it!) the only thing I can think of that could cause actual cavitation is that the inlet to the pump is too close to a wall/baffle and that is not allowing enough water flow into the pump.

There are very little to no bubbles in the DT when I have the valve turned half way off. I am identifying the cavitation by way the pump sounds when the valve is opened all the way. When it is fully open then I get micro-bubbles in the DT.

I am not sure that it is bubbles from the sump. I don't see any and the skimmer isn't running because I am just testing the system with plain water.

The pump has been running for a few days. I immersed the pump and turned it over several times to remove trapped air before turning it on.

I also doubt it is not having enough NPSH because the pump is submerged and there is no swirl from the water surface. The total water level of the return section is 10 1/2". This is not from the pump. From the inlet of the pump without being there I believe is about 8". I would have to check this tonight.

It could be because the return is close to the floor and the back wall. I will try and move it and see if that helps.

 

[cemyth]

This may be a stupid question but you did this while the pump was running correct?

I ask becasue if you did this and the pump still pumped out more water then it took in then where did the rest of the water go? If your tank can handle that much water then it sounds like it still needed more in the system to prevent this. If the drains themselves could not handle that much flow then you would have overflowed the DT. WHich makes me think even more that you filled it first then turned the pump on.

How high up is your overflow?

I did fill the sump to the top when the pump was running.

Not sure about the rest of your questions. My overflow is rated for 1500 GPH and I am only pumping in 330 GPH with the valve half closed. When it is fully opened the pump is very loud but will not pump more than the overflow will handle.

My overflow is at the top of my DT about a 1/2" away from the edge. You can see it in the image on post #4. It is right up against the top support. This was as close to the top as I could get it.

 

[MarkGP]

Sounds like it's not cavitation then. Cavitation is when the water level is too close to the pump inlet and the pump sucks in air from the surface of the water. There is no way that could be happening if the water level is 8" above a mag 12. So from what I gather you are getting micro bubbles in your DT and noise from the pump when you open up the valve to full open. The bubbles could be coming from the sump, perhaps the bubbles created in the sump where the drain water enters. Normally, the bubble trap removes them but not always. One of the downfalls of having the return next to the skimmer compartment. I've always been a big fan of skimmer-fuge-return sumps. Or you could have a pinhole in your return plumbing which is sucking air and creating the bubbles. For the noise, try moving the pump around in the return section. You should have a piece of flexible tubing between the pump and the pvc to absorb vibration. Mag pumps are notorious for vibrating. Also a ziploc bag filled with sand works as a great vibration damper under the pump. HTH!

 

[jwilson]

I agree with Mark, it doesn't sound like cavitation but vibration that's causing the noise. Since the bubbles are only showing up at full flow, I also agree with his thought that you are pulling in air from a tiny leak in your plumbing. My guess would be at one of the unions.
I'm not sure the best way to find it, maybe a spray bottle and looking for the bubbles to stop when water is applied. Hopefully some others have a suggestion.

 

[evsalty]

I am not sure that it is bubbles from the sump. I don't see any and the skimmer isn't running because I am just testing the system with plain water.

.

Use a flashlight and look thru the sides of the sump where the light is shinning. You might be supprised to see a lot of tiny bubbles. If you do this and still do not see any bubbles going into the pump then it could be a pinhole in the plumbing like said above.