Hi Rick, sorry for the long delay in relpying.
My experince has shown that sprayers designed with diaphragm pumps do the least harm to microbiology in compost teas. This is through oberservations using direct microscopy.
In theory, centrifugal pumps do the least harm...this is provided the liquid is going through the pump a very limited number of times. In the real world, we know this is NOT the case when using a sprayer. Sprayers run until the job is done or we're out of compost tea.
The problem with centrifugal pumps is the impeller. As it spins, it can 'slice and dice' the biology. I believe this happens to a much lesser extent with diaphragm pumps within the valve system. I like the fact that (for example) the UDOR Kappa 43/GR has a GPM of 12.5...we can get reasonable volume of liquid out with a reduced RPM at less than 150 PSI. Reduced RPM's mean less opening and closing of the valves. I believe this is the reason we're seeing better results with diaphragm pumps.
With any sprayer, my suggestion is to leave the pump off until it's time to spray.
It makes me a little nuts that 'compost tea sprayers' are being marketed with fundumantal design flaws by people that have never sprayed compost tea. Please, let's have BIG strainers that are properly sized, accessible plumbing for cleaning...and how about aeration systems that work without the pump being on all day. There's several other design details that all add up to better results....and results are what we're being paid for.
I hope this helps Rick.