Will VFD AND MINIMUM FLOW FEEDBACK CONTROL WORK
Will VFD AND MINIMUM FLOW FEEDBACK CONTROL WORK
(OP)
I have a water sump with a sump pump. The flowrate into the sump is variable. The pump has a VFD. There is a feed back loop with a FCV in it(this is to maintain min flow for the pump).
There are 3 signals going to the FIC, which controls the FCV. They are the sump LCV (tied to the VFD), the pressure transmitter and the flow meter in the discharge line upstream of the feed back loop.
Do you see any problem with this design as far as control is concerned?
Thanks.
There are 3 signals going to the FIC, which controls the FCV. They are the sump LCV (tied to the VFD), the pressure transmitter and the flow meter in the discharge line upstream of the feed back loop.
Do you see any problem with this design as far as control is concerned?
Thanks.





RE: Will VFD AND MINIMUM FLOW FEEDBACK CONTROL WORK
If you have molten sulfur or something similar, ok then use a minimum flow.
"I think it would be a good idea."
- Mahatma Gandhi (1869-1948),
when asked about Western civilization
RE: Will VFD AND MINIMUM FLOW FEEDBACK CONTROL WORK
So then you come on with max speed at highest sump level. As the sump level drops, maybe you'll get less flow and can back down on rpm and head needed until flow goes to some minmum, then turn off and let the sump fill again.
There, that sounds better.
"I think it would be a good idea."
- Mahatma Gandhi (1869-1948),
when asked about Western civilization
RE: Will VFD AND MINIMUM FLOW FEEDBACK CONTROL WORK
RE: Will VFD AND MINIMUM FLOW FEEDBACK CONTROL WORK
So, now its when flow into the downstream goes to zero the rpms are down to whatever you need for min flow and the recycle valve's opening up.
"I think it would be a good idea."
- Mahatma Gandhi (1869-1948),
when asked about Western civilization
RE: Will VFD AND MINIMUM FLOW FEEDBACK CONTROL WORK
RE: Will VFD AND MINIMUM FLOW FEEDBACK CONTROL WORK
I use this next one, since many times I don't have FI;
Alternate methods would have the VFD vary the sig from HI rpm to LO rpm based on hi to lo suction pressure (NPSHR). It provides some measure of cavitation protection. If you have a discharge PI, that could act as a high pressure override in to the discharge line. With the LC opening the recycle valve, or the FI opening the recycle valve. Either one could work. Would you rather control off of the level or the downstream flow?
Always another way to skin the cat.
"I think it would be a good idea."
- Mahatma Gandhi (1869-1948),
when asked about Western civilization
RE: Will VFD AND MINIMUM FLOW FEEDBACK CONTROL WORK
RE: Will VFD AND MINIMUM FLOW FEEDBACK CONTROL WORK
"I think it would be a good idea."
- Mahatma Gandhi (1869-1948),
when asked about Western civilization