you are correct Kevin in using the term 'circuits'-hydraulics in the sense of mobile hydraulic power use circuit patterns to route the fluid(oil) in and out of elements(pumps,valves,cylinders and motors) and then back to the tank. Spools are the actual ground and polished control rod parts of the valve that slide in and out of the valve body casting that make the fluid directional changes that control the flow. For my money I'd cap off the fittings on the unused valve ports so there is no possibility of a spool move creating a mess,or otherwise,contamination getting INTO the system.If you are going to place another oder for fittings get a few extra caps and 90's while you are at it that will fit your system hose sizes-put em in a drawer..never know when u might need em..cheaper than separate shipping and waiting on fittings FWIW
