Hi Prahlad,



How I wish I had a blackboard and chalk !! Anyway not to bore the other members, I will keep it brief.

Motors driving hydraulic pumps face a load that is very low in inertia but capable of large step changes. Imagine a pump delivering 50lpm @ 100 Bar. This will translate to an electric input drive power of 10kW. Now I can simply shift a valve in a matter of 50ms to raise the pressure to 200 Bar. ( if 50ms looks fast, I can do it even faaaaster, if I had servo valve ) The new power level is at 20kW. Now you can imagine the kind of PID responses that are required, if you were to hold the rpm display constant. Fortunately the specifications of the rig take this into account and allow for a stabilization period of 100 to 200ms.

This is completely different from a motor driving a large flywheel (like those used in the impact presses). The inertia of the flywheel is so high, that it can "sink" quite large load changes.

The very high power:weight ratio of hydraulic systems is a boon. But it also has its own quirks.

Since you asked, here is the list of set speeds in one cycle :
speed[time in sec)]

Start - 600[5] - 1000[4] - 600[3] - ramp up 4100[5]- ramp dn 2300[2]- 600[1] - stop
And during the above the pressure also cycles in its own independent loop.

Regards

Raghu