thewellguy:
In our small municiple systems, we'd usually have two pumps operate on pressure switches with bladder tanks for storage. I am wondering if I can use the reduced size tanks afforded by VFD's, by using one VFD as a lead pump and another pump controlled regularly.
Steve:
Say my usual demand is less than 30 gpm. I was thinking of have two identical pumps, with different controls. If I have a 30 gpm VFD pump set at 60 psi, then it would be adequate most of the time. As demand increases past 30 gpm (say 40 gpm), the pressure would decrease and start the second pump (at maybe 50 psi). The second pump would immediately start producing ~40 gpm, at the lower pressure, and the pressure would increase back to 60 psi as the VFD slowed down. Then, as the demand decreased, the VFD would eventually turn off, and the other pump would increase the pressure until it cut out.
Is that right? Is that really the way these work? The VFD isn't like cruise control - it won't bleed the pressure off and not allow the other pump to raise it to 70 psi, would it? Is this system recommended? I am trying to have a reliable system, while keeping costs down.