I have a geothermal loop (1" PE) which I am running a set of pumps in series to attain my head height. I know from general rules of pump piping to leave 5-10 the diameter on the suction side to attain uniform velocity. But cannot find information on a min distance between pumps. I'd like to assume the same 5-10 times diameter. But with space considerations, I'd also like a simple nipple connection.