Mag drive started rattling

[mrmaroon]

I have a Mag5 and I recently put a ball valve un to help regulate flow. The thing rattles now depending on how far open the valve is. And the impeller is not loose. It rattles the most when the ball valve is about half open and does not rattle if it is all of the way open or barely open.
Any ideas?

 

[toddpolish]

have you turned it on and off during your process?

 

[mrmaroon]

yes, several times.

 

[toddpolish]

hopefully someone else can help us out here...I've found that with my Mag9.5 I have heard a noise. but only briefly do I hear it rattle somewhat
if I run it for like a second or two without water flowing through it already, it has made some sort of noise.
I can't tell whether it's this or because I've turned it on and off a bunch of times.
However mine hasn't been a problem since I noticed it a couple weeks ago. it fixed itself...I guess. I dunno...
anyone out there that can explain this.
????????????????

 

[scotts]

Question for you, did you put the ball valve on the inlet or the outlet of the pump. You always put the valve on the outlet of the pump. I will try and help you later, but I am having a bad day. I am not familar with the insides of your pump. Can you post a picture?
Scott

 

[toddpolish]

my ball valve is on the outlet of the pump. the pump is NOT submersed. no, I don't have any pix of this...

 

[gatorcsm]

Is your ball valve fully open? Is there any head on the inlet to the pump (that is driving head or pressure) ? How many inches from the water line in the sump to the pump inlet?
Have you looked at the impeller? Have you run it dry for any period of time? Possible that it has worn down the impeller end(s)...
Try throttling the flow down a little bit. What scotts was getting at, is that the pump could be cavitating (water reaching saturation and essentially due to the low pressure, boiling)
Saturation is the formation and subsequent collapse of air bubbles. That can damage the pump, or if it has ever had this happen, caused air binding, damaging the impeller.

 

[mrmaroon]

The inlet is free except for a prefilter. The only time it doesnt rattle is when it is wide open. It has never been run dry. The water lines ias 2-3 inches abouv inlet. I would love to run it full open so it doesnt rattle but then I can't maintain my water level. I have looked at the impeller and I do not notice any damage.

 

[broomer5]

MrMaroon
Couple things I noticed here with your situation.
You say you have to thottle back on the ball valve to maintain the level in your display tank ?
What sort of overflow are you using ?
Is it internal or external overflow ?
If external - is it a DIY or store bought ?
What's the distance from the Mag5 to your return spraybar ~ how much head pressure do you estimate you have ?
Here's a couple ideas I have at the moment.
Magdrive pumps are unique in the fact that they have a magnetic drive. There are two magnets seperated by a wall.
When the pump is allowed to pump "unrestricted" without a ball valve in place, and there is not excessive head pressure on the discharge side of the pump - the pump runs efficiently.
The one magnet ( motor ) drives the other magnet ( impeller shaft ) and the impeller spins freely. Life is good.
If we try to make this pump push water too high up to the tank - it works less efficiently as well. In your case - you may not have excessive head pressure from the return's vertical rise - but when you close off the ball valve - you introduce a lot of backpressure.
Centrifugal pumps do not like backpressure.
Two things can happen when too much backpressure.
1) Discharge Cavitation - this can happen when the backpressure it too high - and is a different type of cavitation than suction cavitation.
The principle is the same - but the expansion and collapse of air bubbles occurs after the impeller - and can cause a lot of noise and rattling.
The cure for this is to increase the ball valve size and increase the return line size.
2) The high backpressure is causing the magnets to uncouple.
When the backpressure excessively high due to the closing off of the ball valve - the water being pumped has no place to go.
It trys to get through the reduced opening in the ball valve - but the flow is so restricted - that the pressure builds up in the pump.
If the pressure builds up inside the pump, and since liquids are basically noncompressible ( for the most part ) .......... the liquid acts against the spinning impeller ( that is driven by tow magnets ) and it's possible for the magnets to uncouple.
The driving magnet on the motor continues to spin. It doesn't care what's going on inside the pump's impeller chamber or the discharge backpressure. It just spins as the electric motor spins.
The receiving magnet on the impeller shaft on the other hand - does care what's going on inside the impeller chamber. If the backpressure get's too high, the receiving magnet may get out of sync.
You know how magnets are ...... positive and negative poles.
Well if the inner magnet get's out of sinc - it has to catch up and get "coupled" again with the driving magnet.
This can also create noise, rattling or otherwise make for a inefficient pump set up.
Are either of these the reason your pump is acting the way it is ? I can't say for sure.
It's possible - but how likely I can't really say.
My biggest concern is your overflow on a 55 gallon tank - that can not keep up with a Mag5.
If your vertical head is around 3-4 feet - that pump will only push around 300-400 gph or so.
Can you describe your overfow, head pressure and more details of the entire set up ???

 

[mrmaroon]

It is an external overflow 3/4''. Not a DIY. Looks just like the rest that you buy at LFS. The pump is definately stronger than the overflow (which is why I put on the ball valve after suggestions from the board).
The sump sits directly under the tank. It goes up about 4 feet to get into the tank through 3/4'' PVC.
I think that if I could tank out one of the 90 degree elbows (there are two) on the drain line, I could speed up the rate of the drain and run the return faster.
Need to think about that one for a while and stop by the plumbinbg store.

 

[scotts]

I have to agree with broomer5, it sounds like when you are throttling back the flow you are exceeding the head pressure of the pump.
Todd, you said that your pump makes noise. Is this a constant noise or only when you turn it on?
Scott

 

[crashlk]

You may want to change to a flow diverter (mixing) valve configuration instead of just a ball valve restriction.
If you divert some of the flow back into the sump, then you can control the flow back to the tank and not create any additional backpressure. Put a Tee inline and use the ball valve to control the diverted water.
This will solve your problem, if you are running a sump configuration. I have used this method with filters and UV's in the past.
Hope it helps

 

[gatorcsm]

that's a good idea crashlk. Seems like it would work for him pretty well.

 

[mrmaroon]

That is a great idea! Hopefully I can do it Friday. Otherwise I am out of the country next week and hopefully my Mag will be ok for a while!