Return line pipe diameter

[piranhaman00]

So the pump has 18ft head pressure. That means psi is 7.8. So on this chart I see floating around, I should assume low pressure or the green section? Around 660gph?

 

[KStatefan]

So the pump has 18ft head pressure. That means psi is 7.8. So on this chart I see floating around, I should assume low pressure or the green section? Around 660gph?

If that is max head then you will get no flow at that pressure.