VFD Operated Lift Station Wet Well Size Question
VFD Operated Lift Station Wet Well Size Question
(OP)
I’m designing a wastewater lift station with VFD’s. I have not found any printed guidelines, etc. about sizing the minimum working volume for the wet well when VFD’s are used. We are flow matching to an extent, however, it would seem as though I would need a design basis for a minimum volume.
The state requires me to have a 15 minute cycle time for my pumps. The pumps can handle 4 minute cycle times. My idea was to get a variance from the state since I’m using VFD’s and then use a factor of safety of 2 and design around an 8 minute cycle time. This will reduce my wet well volume and still protect the pumps. Does that sound reasonable? The other question I have is what Q, should I design around? For constant speed pumps, we design around the total Q, however, this seems really conservative for stations with VFD’s.
Do you have any guidance or lessons learned that you can share?
Many Thanks.
Charles
The state requires me to have a 15 minute cycle time for my pumps. The pumps can handle 4 minute cycle times. My idea was to get a variance from the state since I’m using VFD’s and then use a factor of safety of 2 and design around an 8 minute cycle time. This will reduce my wet well volume and still protect the pumps. Does that sound reasonable? The other question I have is what Q, should I design around? For constant speed pumps, we design around the total Q, however, this seems really conservative for stations with VFD’s.
Do you have any guidance or lessons learned that you can share?
Many Thanks.
Charles





RE: VFD Operated Lift Station Wet Well Size Question
In general, the single pump peak flow approach is most suitable for stations that have relatively rapid flow increase or high headlosses. For such stations, parallel pumping is not as effective, because two pumps operating together yield only slightly higher flows than one pump. If the peak flow is to be achieved with multiple pumps in parallel, the pump station will need to be equipped with at least three pumps: two duty pumps that together provide peak flow and one standby pump for emergency backup. Parallel peak pumping is typically used for large pump stations with relatively flat system head curves. Such operation allow multiple pumps to deliver substantially more flow than a single pump. In addition, use of multiple pumps in parallel provides more flexibility.
You might want to review the Garr Jones book, Pumping Station Design.
http://nepis.epa.gov/Exe/ZyNET.exe/901U0X00.TXT?Zy...
RE: VFD Operated Lift Station Wet Well Size Question
Thanks.
Charles
RE: VFD Operated Lift Station Wet Well Size Question