Backyard Aquaponics
A place to discuss aquaponics

About 6 weeks ago I got a 1,800 gph pond pump which did really well for the first 3 weeks. Then it began slowing down and is has been pumping about half as much as it once was. I have taken the whole thing apart hoping to find a leaf or something clogging it, but found nothing . The impeller freely spins a 360 degree angle but will not turn farther than that... maybe that has something to do with it?
I blasted the pipe leading to the grow bed with a hose hoping that might unclog some debris but that did nothing either. When we first got the pump it was silent but now you can hear the motor running if you lean in near the water.
The pump runs continuously but one night it was accidentally unplugged and so it remained off for a good 12 hours. The next morning I discovered it was off and when I plugged it back in it was working stronger than the previous day. It seemed to be pumping slightly more than usually for a day or so after its break, then died back down.
Any ideas on what is wrong and how I can fix it?
Thanks

Could be a couple of things, the impeller shaft getting a bit stuck so not spinning well, or perhaps the impeller spinning on it's shaft.. Can be diagnose both of these problems...

Hi Delilah:

Your pump had two sponge filters on it - did you remove those or are they still on there? The inlet pipe can get clogged as well as the outlet pipe, and those filters would easily strangle the pump's flow if they are on there and clogged.

BTW this morning I had to clean out my aquarium system's pipe. It gets slow after awhile because of crud getting into the pump and slowing the flow. Today I got that cleaned and a huge plug of black goo was squirted out of the hose. Crud can build up in pipes, and especially in rubber hoses for some reason (I had the same slowing issue when using garden hose before).

shutting it off probably caused a backflush of any water that was in the pipes to go back through the pump into the tank, .. so it was stronger for a bit..especially if there's a anywhere inline?

I did removed those filters (by the way, thanks for the help with that )
Strange thing is there is no gunk anywhere in the pump or tubing. I spoke with a fellow at a pond supply store who reckons it might be a manufacturing error having something to do with the impeller.

The pumps I've had make a loud noise before dying, it gets louder before they stop. Kind of a scratchy vibration noise.

Funny you say that, I have noticed it getting louder a scratchy vibration is exactly what it sounds like.

Hi Delilah,





If your pump ran really well for the first three weeks I would suggest that it’s not a manufacturing error. I don’t know which brand of pump you are running, but of all the brands that I have sold over the years, none have offered warranties on the impellor. I have replaced impellors for customers on the distributor’s authority when a customer has returned with a faulty impellor within a few days of purchase. Normally if there is a manufacturing fault, it is evident from the outset, or within a couple of days.

Are you throttling the flow of your pump?... ie: is your pump bigger than what you need and you are slowing the flow to the GB using a tap?... Restricting water flow in this way can cause cavitation, which damages the impellor.

If you need to reduce the flow to your GB you can put a tee in the main line between the pump and the GB, with a line from the tee returning to the FT, put a valve in this return line and use this to regulate the flow at your GB, the more you open it, the less flow you will get at the GB. This will eliminate the back pressure on your impellor and stop cavitation.

Another possibility is an air lock in the pump, this will cause it to be noisy and have reduced flow. This causes cavitation and can also cause the impellor to heat up, damaging it. With the pump running, try jiggling it around and tipping it over slightly in all directions, if it is an air lock the pump will quieten and pick up flow when the air lock is removed. If air locks are your problem, when replacing a pump after cleaning etc, it’s a good idea to run the pump in position first without the line connected (if possible), then reconnect the line to the pump while it’s still underwater, preferably while it’s running.

If you have a standard pond type submersible pump, remove the impellor, hold the magnet end of the impellor firmly, then turn the actual impellor blades with your other hand, they should turn almost full circle (about 320º) then stop. It should turn freely back and forth through this 320º, you shouldn’t be able to spin it completely around, otherwise your impellor is damaged.

Cheers.

I have 2 6000lph barracudas pumps that have done the same thing. Been pulled right apart and while there was an improvement not anywhere near like original flow.
Was a bit of buildup around the shaft before I cleaned them but spins freely.
Not really noisy however.

Well I'm pretty sure now that the problem is in pipe that leads to the grow bed. I switched the original pump with a diffrent pump and now the new pump is going slower too. So now rather than a problem with the pump I think it's with the pipe that leads the water to the grow bed. I used a garden hose to blast the pipe in hopes of dislodging some gunk and then reconnected it to the pump. That seemed to make it stronger... not perfect but better. rather than going half it's original strength its probably going three quarters as much now. I guess I will just buy a new tube (they only cost a few dollars) but I'll have to figure out how to keep it from gettig clogged again.

What is the diameter of your pipework from the pump? I've posted elsewhere about using larger diameter pipe:
"I've forgotton nearly all my chemical engineering, but I'll try to give a basic outline of pipe size.
All pipes have pressure losses due to friction. Larger pipes have less pipe surface when compared to cross sectional area, so for any given length of pipe, a larger pipe with have less pressure drop due to friction than a smaller pipe. All fittings, valves, bends etc also reduce pressure, and again, the larger the pipe the lower the pressure drop.
Correctly sizing pipes is important because the pump you use must be able to pump the water to the correct height at the required volume. It is easier to add pressure loss with a valve than it is to try and reduce pressure loss.
There is some evidence that running pumps with a constricted outlet (eg undersized pipes) will damage it in the long term, but this is better left to people in the industry."
Try this site to see the effect of pipe diameter on pressure drop:
http://www.huntermac.com.au/popuppages/ ... pvc_12.pdf

Smaller pipes also get blocked or crudded up more easily.

Thanks for all that info, really helpful The pipe I was using was a 1" diameter pipe however it had gotten a build up on algae on the walls. The new one I got is 1" but works a lot better, I'm guessing because of the clean walls. so now my pump is working the original speed it was when I first bought it

I tend to upsize plumbing from the pump for most of my systems. I've found that a tiny pump that tends to really slow down when hooked to 1/2" plumbing will keep going much better with 1" plumbing and I've plumbed many pumps that have 1" outlets to 1 1/2" pipe for the first leg of their journey.