eheim air pump low pressure

[ScareCrow]

Hi All,

I've got a second hand eheim 400 air pump that to me seems to output quite low pressure. I've got two hygger piezo air pumps that came with air stones. I've tried to power the air stones using the eheim pump and nothing comes out, where as the hygger air pumps run them fine.
I've taken the eheim pump apart and nothing seems out of place, the diaphragms seem supple still and it's not producing much noise like air pumps do when the diaphragms need replacing.
Is this normal? I can't find any pressure specs for the eheim but notice it does normally come with an eheim diffuser so I'm wondering if this is less restrictive compared to the normal air stones.

Thanks in advance.

 

[JohnCooke]

I have the same airpump. If you connect it up to 1 or 2 airlines, without airstones, and put the airlines in the water, is it producing bubbles? [Do ensure you have non-return valves fitted before trying this!]

 

[ScareCrow]

I have the same airpump. If you connect it up to 1 or 2 airlines, without airstones, and put the airlines in the water, is it producing bubbles? [Do ensure you have non-return valves fitted before trying this!]

Yeah air comes out of both outlets fine and I forgot to mention both flow rate controls also work as expected.

 

[Maf 2500]

How old are the airstones? Might be partially clogged, and the Eheim not producing enough pressure to overcome this. When I researched the piezo air pumps a while back I was very surprised by the very high air pressure compared to low air volume pumped in this design.

 

[ScareCrow]

The air stones are brand new.
I was thinking that the piezo air pumps may produce more pressure than the eheim but I couldn't find any specs on pressure output for the eheim so not sure. Surprised it can't push air through the air stones though. I even tried connecting both outputs to a single stone but nothing.

 

[Maf 2500]

How deep are the airstones? have you tried holding them just under the water surface? Would make a difference if it is pressure related.

Might be worth measuring the volume of air output by the Eheim, which would likely be seriously reduced if it is faulty. (Time how long it takes to fill a submerged container of known volume)

 

[ScareCrow]

Just under the surface it will fizz slightly any deeper and there's no output at all.
Good idea about the volume output, I'll test and see how it compares to the specs.