Originally Posted by Gregcoyote
I have the same Iwaki pumps I started with. I put hot tub style strainers on the intakes so they couldn't ingest anything that wouldn't go thru the impeller. I have never back flushed the pumps or done any maintenance on them except keeping the cooling fans unobstructed. Guess I'm lucky, but it turned me into a Iwaki fan.
Certainly didn't mean to say you bought cheap valves. I meant that as recommendation to not buy a flapper style valve over the plunger type. No insult meant.
I also have strainers on the pumps
But its still good to back wash them every now and then it dislodges any slim you get on the impeller or in the pipes
Plunger or flapper valve they all fail
I have plunger type air non return valves and they have also failed in the past
Air pump non return valves also restrict air flow please don't tell me they don't
Unless the diameter of the pipe you install the valve in isn't changed in anyway then its kind of obvious they will restrict flow to some extent