I'm having a discussion about the pressure in a flexible line. The concern is there is a rigid connector joining two flexible lines of the same diameter but the connecting piece is $40$ % smaller than the two transfer lines. The pump output is variable and at maximum flow rates, the pressure preceding the rigid connector may prove to exceed the capacity of the flexible line, not to mention added stress on the pump itself. I'm told if the pump output is within the tolerance for the pipework, then there is no inherent danger of failure of the flexible pipe, but it is still inefficient at least.
I have expressed concern but been told it's not a problem, yet there is observable dilation of the flexible line prior to the connector. I have little knowledge or qualification in this field so I find myself unable to present a cogent argument backed up with empirical data. If someone could show me a formula to calculate the disparity in the pressure on either side of the connector or how the restriction could cause peaks in pressure prior to the connection it could prove useful.