Air in Pump when Backwashing Sand Filter

[curtis1031]

Hi friends,
I am fresh to the pool system. When I do normal filtering mode, it works fine (small air bubbles underneath pump lid and remain same size). I assume there is no leakage from entry side (o-ring and water inlet pipe). However, I found a headache on getting air in pump when I do backwashing my sand filter. Just wondering why the problem comes from and how to check/fix?
Thanks for every answer.

[Denniswiseman]

What happens when you vacuum, because if you have a suction side air leak it shows up more when vacuuming

[curtis1031]

Thanks. I haven't yet tried vacuuming. Can I ask what's the reason? Mine is an in ground pool and water surface is above the pump and possibly above filter. When it's operating the water level is half way above the skimmer entry.

[Denniswiseman]

Thanks. I haven't yet tried vacuuming. Can I ask what's the reason? Mine is an in ground pool and water surface is above the pump and possibly above filter. When it's operating the water level is half way above the skimmer entry.

The idea is to find out if you have a suction side air leak
Irrespective on where your equipment is situated you can still suck in air (probably around the pump)
I had a suction side air leak that was on a pump seal when vacuuming

[curtis1031]

Does it mean a air leakage from pump suction side? But how to explain when doing filter (which still suck water from pump) there is no air bubble? Thanks

[Denniswiseman]

It all depends on the extra load being put on the pump
All pools are different, just try vacuuming and see if there is any difference