Originally Posted by NATO
If you think about it though, the pump is mechanically designed to operate at a particular speed with no restriction on its output, if you clamp or restrict it in any way you are forcing it to work against this which will hurt it in the long term.
The manual I found online
There's a description in that manual on how to reduce airflow by bleeding off excess pressure with another outlet, have a quick skim over it.
Diaphragms are cheap enough to replace when they eventually wear out, but they last a fair while. I don't like to have an open outlet because its too noisy. If I'm not using all my outlets, I pop a piece of airline tubing onto it with a check valve inserted back to front.
If you put a 4 way splitter on a single outlet, then block one of them, then the air is just pushed through 3 instead of four outlets. Which is more than the original one outlet. I may very well be using false logic (I'm known for that) but it makes sense on my head. Lol!
My large air pump is electromagnetic, and WAY more powerful than I need. Until I can get hold of some of the little clamps, or the valves with the little taps on them, I have tied loose knots in the lines that go into tanks with fish that don't appreciate the turbulence (like my ember tetras). The outlets I don't need, I have blocked off with check valves.