The important PSI is not during the back wash, but after, when running normally.
When I got my house and first started running the pool/pump, normal pressure was about 14 to 15 PSI.
I have two returns, the main drain and the skimmer.
We had valves on the returns, so that is was possible to turn off one, the other or both.
With both on, 15 psi, with just one on, 8 psi.
When the pressure gauge hit about 22 psi, we could hardly hear the ventury air ports for some of the pool jets.
It was time to backwash, then the psi returned back to 14 to 15 psi.
Then our pump motor died and we replaced the pump with a Hayward Northstar (more pump than I need, I guess, but I like it).
The pressure gauge now reads for normal about 24.5 to 25 psi.
The Northstar is a stronger pump, with a faster flow rate, thus the greater pressure.
The pressure depends on the size of pipes, the length of the pipes and how many bends in the piping.
The pressure also depends on the filter used.
The pressure obviously depends on the pump.
