The vineyard I work at has a tow-behind air blast sprayer for applying fungicides, insecticides, etc. to the vines. It uses a 3-cylinder piston pump run off a tractor PTO to pressurize the water, and the manual calls for a SAE 30 motor oil of at least SG? spec. What oil will be most appropriate for this application? Spins at less than 500 RPM, generates about 300 PSI, not much heat but a lot of moisture present.