What I’ve heard from the Soil Food Web people is to use diaphragm pumps and also to consider the plumbing. Avoid sharp 90° turns. They can really kill biology I’ve heard. It’s mainly about velocity and impact. Larger tubing, sweeping bends, large nozzles, larger pump running slowly, etc. so that the solution is moving slower should be helpful. The main reason to keep pressure lower if I understand correctly is to keep velocity down. But if you’re spraying 30′ high on a tree, high pressure is not as bad because the velocity is reduced by the time it reaches the tree… I haven’t done microscope testing on sprayers myself but some people talk about seeing half or more of the larger microorganisms being damaged in a poor sprayer setup.