The rubber impeller spinning in the housing lowers atmospheric pressure within the pump cavity and the pressure differential causes water to flow into the cavity. To be technical. Suction is completely different. I was actually awake during hydraulics 😂

I wasn't, I like suction, it's fun to say😁

The lines cannot be 'primed' unless you have some sort of bleed just before the inlet of the pump. An impeller pump is a PD pump or Positive displacement. The inlet is 'sealed' from the outlet so you cannot run water into the inlet due to the inlet being 'airlocked'.

This of course assumes that the impeller and housing are in good condition.

Also to answer the question about suction: Yes PD pumps do produce suction or a bravo style impeller would never see water.

I 100% agree with you.....i only did that to get the liquid up to the impeller quicker during cranking so it wasn't left up to the impeller to try and pull out of the drum it was in. When the boats in the water, the water line is above the seawater pump and when you start to crank the water will force its way in easier...even though the impeller is trying to suck it in at the same time. By using the bilge pump on startup i figure the impeller is working less hard and is less likely to get damaged trying to pull liquid into itself. Im probably overthinking it but i hate contorting myself to get the seapump out to change impellers so anything i can do to prolong its life between changes is good for my back!

Actually...this whole conversation reminded me of something. About 20 some odd years ago when i started working for the pump company i'm at right now...we tested a merc seawater pump just to get an idea of our mag-drive system could be used on a rubber vein impeller style pump. If memory serves me well i think we either had a 1.5 or a 2hp electric single phase 220v motor hooked to it. It didn't have enough starting torque to get it moving from a dead stop! Once it was given some help by hand it took off. Those pumps can do some decent volume of liquid and they generate some impressive pressure! Again if my memory is correct it did somewhere in the neighborhood of about 85-90' of head height which translates to just under 40psi! Im not sure how good the impeller was in the pump we tested so a new impeller and new housing may generate even more pressures!

OMG!!!! ROTFLMAO!!!

Need to watch more South Park.