Is it normal to have air built up at the filter relief valve

[mkmscr]

So I have cleaned my DE filter a few times. Perfect article, thank you. However, since my last cleaning I seem to always have air built up at the filter pressure relief valve when I open it. Only takes about 3 seconds and air is replaced by water. Is it normal to have air built up at the filter relief valve or should it pretty much stay charged with water once the air is released? I don't have bubbles in my pump basket and I usually don't see bubbles from the returns (unless it's just starting up). Am I being paranoid by releasing air once a day from the relief valve? Is it normal to have air at the relief valve?

 

[Sminor]

That's common if you have a bad seal or tiny air leak somewhere in the system. Top of the filter is typically the high point so that where the air will go. Of it just started since last cleaning I check the seal on the filter. Lube it up again and make sure she is nice and tight.... Ha