Thanks for your report. There have been various changes to fluid systems over the last 6 months, and there was a bug with fluid being passed across multibodies which was fixed. This may have fixed this issue.

Otherwise, there is resistance caused by most fluid parts such as valves and this is just how the fluid system works in Stormworks.

For water cannons, it is best to put a pump after any pivots / valves, pushing water straight into the nozzle.