There are a good many "tips and tricks" employed by hydraulic systems engineers...
Hammering valves onto seats...
Grinding the edges of valves to make them spill in a slightly different way...
Packing springs...
Dangerous little short-cuts that get the job done...
Stuffing a piece of wire in a choke to avoid re-drilling a hole or to stop crap blocking the orifice in a dirty system.
There are no equations or formulae that can explain how or why they work, they just do. You will struggle to find published data on these "actions" as putting them into print tends to leave the author open to all sorts of lawsuits.
From experience, they work... actually they work very well. Just make sure the can't come out!!!
Adrian