CSV with VFD

[gsb]

Hi,
Is it possible to use a VFD and a CSV on the same system? The VFD would be used as pressure switch kind of..

Thanks

[Cary Austin]

Yeah, we do it all the time.  It is basically using the VFD as a soft start.  One way is to set the CSV to a lower pressure than the set point of the transducer.  The pump will run at full RPM and the CSV will control the pressure and flow.  When there is no demand, the bypass in the CSV will allow the pressure tank to fill to the PID set point, and the pump will "go to sleep". Then the setting of the "sleep mode" iin the VFD will determine how low the pressure and pressure tank goes before the pump "wakes up".

Another method is to do away with the pressure transducer, and use a regular pressure switch to control the VFD like it is just a soft starter.  Then the pressure switch and CSV settings are as they normally are.

Either way you are running the pump at full speed while the CSV reduces the flow and amps while maintaing a constant pressure.  Always running at full speed keeps the pump from running through any "critical speeds" that normally causes vibration when varying the pump speed.

[gsb]

Tanks for the help.
I am using a CSV1A and I have a Franklin Monodrive that is not presently connected. If I understand well I can use the mono for soft start and this is what I want to do. The pressure switch (that they call a censor but it is not, it is a low pressure switch) is adjusted at 60 psi which mean that the motor will start at 59 psi if I understand correctly. Presently the CSV1A is adjusted at 50 psi and I am using a standard 40-60 pressure switch and a control box to start the pump motor. If I want to use the Franklin what would be your settings recommendations for the Mono sensor and the CSV1A? I do not understand how I can use the mono which has only 1 psi deferential pressure between start and stop.

[Cary Austin]

With the 1 PSI differential pressure switch that comes with the Monodrive, we can’t let the pressure drop and use the water out of the tank before the pump starts.  But once it starts, the CSV will pull it down and keep it at 50, and not let it build to 60 and shut off as long as you are using water.  The 40/60 pressure switch would be much better.

However, you don’t need the Mono Drive for a soft start.  The CSV will do that for you.  We have learned that starting a pump against a CSV gives the same reduced amp start as when varying the motor speed.  Starting a pump against a CSV is like starting an unloaded motor.  Sometimes it even starts with fewer amps than when using a VFD.

Also ramping up the speed of a submersible is much harder on the thrust bearing than letting it start at full speed.  Any rotation below 30hz or half of full speed will not lubricate the thrust bearing and will grind it off.  It takes 30hz or half of full speed to get the hydroplane effect needed to make a Kingbury type thrust bearing work like it should.