I have a sand filter that ran at 28 psi all last summer when clean, and would increase to 32-33 psi when dirty and flow would essentially stop until I backwashed. Then it came back down to 28ish, and flow would be back to normal. During the off season, I plumbed in a saltwater chlorinator between the filter and returns (no heater installed), and now when I opened up my pool and started up my pool pump, the pressure has increased to 45 psi. The filter is clean, I think, because the flow is pretty normal out of the returns.
I am worried, because the max working pressure on my sand filter is 50 psi, so I'm worried this is a bomb waiting to explode. Any idea of why the pressure would be so high after winterization, plumbing in the new SW chlorinator, and opening for this season? My first thought was the plumbing changed, but I dont see much more resistance in flow than how it was previously plumbed, that would make it go up by 20 psi.