Troubleshooting sponge filter

[Jim Sinclair]

Thank you for those detailed instructions. They were so descriptive that even I, with very poor visualization ability, was able to follow them and recognize what I was looking at when I opened up the pump.

But when I opened it I could not see anything wrong with the diaphragm or flapper or anything else.

I took it to my favorite LFS. The guy there spent about 20 minutes examining it and checking the different parts and exclaiming about what excellent condition the pump is in considering it's an old one that came with an old Craigslist aquarium. He said the diaphragm and flapper are in pristine condition.

After removing and examining all the components, he put it back together and plugged it in. We could feel air blowing out of it.

Then I thought perhaps the problem is not in the filter (which is working very well with a different pump), or in the pump (which appears to be in great shape), but with the airline tubing, which is not only old and stiff but has also been chewed on by cats. Maybe there were tiny micro-punctures in the tube which reduced the air pressure coming out the other end.

With this possibility in mind, I came home and unhooked the brand new
airline tubing from the brand new pump, connected it to the old pump which had just received a clean bill of health from the LFS guy, and plugged it in.

And nothing happened. The filter works fine with the new pump and not at all with the old pump, with the same tube used on both trials.

Do you have any other ideas that might make it possible to salvage this pump?

Diaphragms can be repaired cheaply and easily. You simply buy a replacement diaphragm for that specific pump and swap it over.

Turn the air pump off and unplug it.

Turn the pump over and look at the bottom of it. On the bottom of the pump should be 4 or 6 small screws that hold the case together. Undo these screws and separate the top and bottom halves of the pump case.

Inside the pump will be a coil (a couple of thin metal plates with some copper wire wrapped around it. DO NOT TOUCH THIS because it will be hot and if there is power going to the pump you will get zapped.

Inside the pump will be a metal L shaped arm with a magnet on the end. The magnet will be next to the coil. This L shaped arm is attached to the rubber diaphragm. You need to remove the L shaped arm and diaphragm together. They are sometimes held to the case by a screw and sometimes the metal arms simply pushes into a rubber grommet.

Once you have removed the arm and diaphragm you separate them from each other. Check the diaphragm for holes, tears, splits. Take the diaphragm to a pet shop and get a new one that is the same height, thickness and diameter as the old one. Check the diaphragm for squishiness too. Sometimes the rubber is harder or softer than it should be and they don't work properly. I usually buy a couple of diaphragms just in case one is dodgy.

Put the new diaphragm on the L shaped arm.

The diaphragm fits onto the air chamber. The air chamber has a couple of small thin rubber flutter/ flapper valves that sometimes get holes in and this will also stop the pump from pumping air. Check the valves for holes. If they have any you will need to replace them. They can be bought from the pet shop.

Once the air chamber has been checked (and repaired if necessary), put the air chamber and diaphragm back together and put the L shaped arm back into its spot. Plug the pump in and turn it on. Connect some airline to the pump outlet and see if it works. If it does, then turn the pump off, replace the base and screw it back together and away you go.

Diaphragms can be repaired cheaply and easily. You simply buy a replacement diaphragm for that specific pump and swap it over.

Turn the air pump off and unplug it.

Turn the pump over and look at the bottom of it. On the bottom of the pump should be 4 or 6 small screws that hold the case together. Undo these screws and separate the top and bottom halves of the pump case.

Inside the pump will be a coil (a couple of thin metal plates with some copper wire wrapped around it. DO NOT TOUCH THIS because it will be hot and if there is power going to the pump you will get zapped.

Inside the pump will be a metal L shaped arm with a magnet on the end. The magnet will be next to the coil. This L shaped arm is attached to the rubber diaphragm. You need to remove the L shaped arm and diaphragm together. They are sometimes held to the case by a screw and sometimes the metal arms simply pushes into a rubber grommet.

Once you have removed the arm and diaphragm you separate them from each other. Check the diaphragm for holes, tears, splits. Take the diaphragm to a pet shop and get a new one that is the same height, thickness and diameter as the old one. Check the diaphragm for squishiness too. Sometimes the rubber is harder or softer than it should be and they don't work properly. I usually buy a couple of diaphragms just in case one is dodgy.

Put the new diaphragm on the L shaped arm.

The diaphragm fits onto the air chamber. The air chamber has a couple of small thin rubber flutter/ flapper valves that sometimes get holes in and this will also stop the pump from pumping air. Check the valves for holes. If they have any you will need to replace them. They can be bought from the pet shop.

Once the air chamber has been checked (and repaired if necessary), put the air chamber and diaphragm back together and put the L shaped arm back into its spot. Plug the pump in and turn it on. Connect some airline to the pump outlet and see if it works. If it does, then turn the pump off, replace the base and screw it back together and away you go.

 

[AmandaN]

Palmer Aquatics just did a pretty good hour long livestream talking about sponge filters in details. Maybe it will help you to understand.

 

[Colin_T]

Did they change the diaphragm in the pump?
Diaphragms can be the right size and shape but sometimes they are too hard or soft for the particular pump. If you use a diaphragm that is too hard or too soft for that specific pump, it will run but not have any air pressure, (it won't be able to pump air to the bottom of a tank).

If the diaphragm is attached too tight or too loose to the arm, it won't pump air properly.

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The air chamber has 2 flapper/ flutter valves in it, one on each side of the air chamber. Did they check both sides of the air chamber?

Did they change the flapper/ flutter valves?
These can look good but still let air leak through when they get old.

If the air chamber and diaphragm look good, try putting a new air chamber and diaphragm in.

I use to test air pumps at the shop after I changed things in them, just to make sure they worked so customers didn't go home and have to come back again.

If everything has been replaced and it still can't pump air, the only other reason would be a drop in power going to the coil. If there is not enough power in the coil, the metal L shaped arm won't move fast enough and you won't get any air when the airline is in the water. However, the coils are normally pretty reliable because it is a non moving part and consists of copper wire wrapped around an iron rod.

If there is a power drop in the pump there is nothing much you can do about it. If you know an electrician, you can get them to check the electrical side of the pump but if you don't know one, don't bother getting it tested because it will cost you more to have it tested by a sparky than it would cost to replace the pump.