Well aren't I a dummy. When I start brewing with my Elektra, the brew pressure needle initially bounces around in the 3-5 bar range and the machine is quite noisy, before the needle settles at 9 bar and the machine quiets down. Turns out I didn't know how to adjust the pressure reduction valve, so the line pressure was (apparently) too low. I turned the pressure up and now the bouncing needle/noisy pump only lasts for a second. I guess I will try turning the pressure up more and adding a pressure gauge to the line so I can actually see what I'm doing. The supply line is 3/8" poly which seems sufficient, and it will be hard to use anything larger. Hopefully I didn't damage the pump, but I have a spare Procon pump anyway.

The Pump Pressure gauge 'should' measure the water line static pressure when the pump is not engaged. ⅜-inch water inlet pipe should be fine.