VFD with conventional pressure switch

[edwards1800]

Related to this thread-
Can I use a VFD set at 60 psi, and a backup well (set to cut in at 50 psi, and shut off at 70 psi) on the same system?

 

[thewellguy]

Need more info on the set up. How many pumps, how are you controlling Ect

 

[SteveWag]

Yes, you can, but the VFD will shut down as the backup well goes from 60 to 70 PSI. If the backup produces more water(say twice as much) than the VFD well it should work. But if the VFD well is the larger of the two, and the pressure drops to 50 PSI (why, because of demand?) and starts the backup, as the backup gets to 59-61 PSI you would loose your main source.

Steve Wagner

 

[edwards1800]

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.

 

[thewellguy]

Edwards,

If sounds like you have a pretty good handle on it. I have set up systems like this before. I would run pump one off a pressure transducer just like you suggested. The second pump could have an across the line starter and run off a pressure switch.

There are two manufactures that have systems set up for applications like this. The drives come with software already programed for an application like this. Berkley and yaskowa that incopterate this into one unit. There may be others taht I am not aware off.

I would strongly suggest that you consult with a well pump installer in your area about the programming. No disrespect to the othr trades, But I have yet to meet an electrician that understands submersible applications.