1 vfd / 1 soft start
1 vfd / 1 soft start
(OP)
Hi, I am having a little trouble with my system. I have 2 300hp motor's powering 2 1,000 gpm pumps. Pump 1 has a vfd drive and pump 2 has a soft start. My system flow is constantly changing but pressure must reamin the same. Pump 1 will run on the vfd fine, and when it reaches 100% pump 2 will kick on and take over the flow. Pump 1 will then ramp down and take over the remainder......my problem is that when the system flow is at 1050-1150 it is in the middle of both pumps and excesive cycling occures on pump 2.
How can i narrow this margin? Would lowering the max. output on pump 1 vfd help?
How can i narrow this margin? Would lowering the max. output on pump 1 vfd help?





RE: 1 vfd / 1 soft start
Solutions / workarounds.
1.) Don't operate at that problematic range.
2.) Remove the VFD and add discharge pressure control valves.
3.) Keep the VFD and add a recirculation line to pump 2 back to the suction manifold to increase the suction pressure of both units, lessening the load and discharge pressure of pump 2 while enabling a more balanced discharge pressure to be produced by pump 1.
4.) Junk the VFD and add a recirculation line from discharge manifold to suction manifold that includes a pressure control valve, which is adjusting flow from discharge manifold to suction manifold to control the pressure in the discharge manifold's to whatever pressure you need to flow downstream.