As the pump is rated at 1070 rpm, the belt gearing looks like the motor is approx 1400, you could quite easily slow it down to reduce the power required, so if it was to go to 600 rpm then the required power would be 3 (ish) kw it would be slower building up BUT the advantage would be it will be considerably quieter. And last for ever.
two stage pumps are slightly easier on the required motor torque also.
You might have to fit an unloader solenoid on a timer to the feed pipe to help it get to speed if on single phase for first 30 seconds or so and then that would close allowing the pump to then get loaded as normal.
No dont lighten it, it needs that flywheel to do its work as said just unload it with a solenoid valve or what you can do is have the engine movable- ie self tensioning capable, then you can start it with no load as per ride on mowers and use the belts as a clutch.After thinking about it a bit, it seems to me that the initial inertia is down in part to the heavy flywheel / pulley wheel. I wonder if its possible to fit a lighter one, or hack some weight off the one thats on it. With an unloader valve and new bearings a petrol engine might turn it.
mine was a 20hp twin lister diesel direct drive to a 90cfm v twin pump that was no joke when cold[/QUOTE]with them unloaded or not.
I bet it was !! that sounds like a candidate for a fan heater on it for and hour before cranking time !![/QUOTE]yes in winter I had to . was nearly a heart attack jobmine was a 20hp twin lister diesel direct drive to a 90cfm v twin pump that was no joke when cold