Csv in a dairy

[Dairy Guy]

I have a dairy with roughly 2000 head of cattle and am looking to install a csv. My current setup is a 7.5hp 3 phase motor pumping into a 1500 gallon air volume controlled tank through a 3" steel line with a 40/60 pressure switch. I know the standing water level is around 130' but I don't know much more than that. The pump was last pulled around 20 years ago by a company that no longer exists and I wasn't even at this dairy at that time.  My current pressure tank is in  dire need of replacing which is the main reason for me looking into a different setup being as pressure tanks are so costly and a csv system doesn't require such a large tank. So my questions are: can I install a csv with the limited information I have? A dairy is a 24/7 operation and I am relatively certain that at no point will the demand be less than 5gpm which will cause the pump to constantly run with absolutely no rest, will that be an issue? I understand that by limiting the gpm the amperage is also reduced however a pump that normally pumps say 50gpm being reduced to 10 gpm wont see a 1/5th reduction in amperage correct? So I can expect to see an increase in my electrical bill? A csv will cause higher pressures between the csv and the pump, could that be an issue with a pump and pipes as old as mine? Lastly assuming my system is a good candidate for a csv what size bladder tank and what model csv would I need? The inlet into my current tank is 3" but the outlet is only 2". My pump guy is pushing for a vfd but I still have most of the same concerns with that and it's a more costly system that isn't very reliable. Any help would be greatly appreciated. Thank you.

[Cary Austin]

Hi Dairy Guy
We have done lots of dairies with CSV's in the last 25 years.  Many of them were installed to replace VFD's, as they are so expensive and give so many problems.  But most CSV's just replace huge pressure tanks in systems like this.  Yes the flow will only be about 1/5 of max when the amps are about 50% of max.  This is exactly the same thing as happens with VFD's.  Just VFD salesmen will show you the 50% reduction in amps and tell you they are saving you 50% in energy cost, when they are actually increasing the cost to pump each gallon of water by as much as 500%.  However, if the pump isn't too much over sized, and is running close to a 7.5 HP load most of the time anyway, the added energy cost for the times it is pumping at low flow won't increase the bill by much.

When there are lots of variation in flow a 2 pump system can save considerable energy.  If you have another well on the property, a 2HP +- could be the primary pump that runs 24/7, and the 7.5 HP would only come on when more than 20-25 GPM was needed.  This reduces energy and takes a lot of wear and tear off the big pump.  Many times the Dairy owners house well is just teed into the line and used as the primary pump.  Turning the pressure switch on the small pump up to 45/65 makes it comes on before the large pump with a 40/60 switch.  If less than 25 GPM is being used, the 2HP is the only pump running, and maybe only drawing a 1HP load if the CSV is restricting the flow to match small demands.  If the 2HP pump quits, the 7.5 HP will automatically come on and supply the house and Dairy as needed, drawing a little more power until you get the small pump repaired and back to running.  Either of these pumps, as nearly all pumps, are made for "continuous duty".  Meaning they are made to run 24/7, and will actually last longer running 24/7 than when cycling on and off all the time.

But even if you do not have a smaller well or water supply to handle the lower flow rates, the energy for running a 7.5 HP won't go up much if at all.  Many times just eliminating the multiple on/off high amperage starts every day will lower the electric bill.  But even if the electric bill goes up some, it will be more than off set by what you are saving on pressure tanks and by making the pump last much longer.

With a single 7.5HP pump you will need a CSV3B2T and an 86 gallon size tank.  With a 2 pump system I would put a CSV1A on the small pump and a 44 gallon size tank at each well instead of one 86 gallon tank.