Since we already have all the VFDs that would be tough to explain to the board but I'm looking at it. One of our issues is power sometimes fluctuates and the VFDs don't allow the pumps to run in that situation which supposedly saves them from possible damage. We do have two independent pumps that handle tennis and pickleball and those don't have VFDs so possibly those are using CSVs and they do run when the power is flakey but the courts need to be watered. I'll check.
Since one of my concerns was having the jockey running when I thought it should be idle I'm a bit relieved that you think it should run 24/7. WorthFlorida mentioned that as well.
Actually the system works very well, I'm just trying to understand how the pumps decide which runs and whether the pressure should always be around 70 or if it's ok if it's running at 65 for a while. The heads seem happy. I looked at station 2 (with the jockey) around 8pm yesterday and the jockey was happily churning out its 100gpm while some other pumps were running elsewhere, then later it was stopped and the 30hp pump was putting out 330gpm. Something told the jockey to shut off.
Since pumps kick on when the pressure drops below 50, if two pumps are on and it's running at 65 no other pumps will run so it stays there until more zones come on or turn off. I find it fascinating. I need a new hobby.
The idea of using a VFD to vary the pump speed and flow to maintain a set constant pressure is a fantastic thing. I was fascinated with VFD's 30-40 years ago when I was selling and installing them. I still keep up with the new trends in VFD's, as they have been telling me the next generation is going to solve all the problems of the last generation about every 18 months for the last 30 years. Lol!
What I learned 30+ years ago is that using a valve to vary pump flow to maintain a set constant pressure can work even better. The hard part for most people to understand is that restricting the pumps flow with a valve decreases the amp draw or energy use almost exactly the same as when using a VFD to vary the speed.
Most likely it is the VFD's that are having problems with the quality of the power in the area, not the pumps. Most regular squirrel cage induction motors are fairly robust, and can handle quite a bit of variation in voltage and even phase unbalance. Regular across the line magnetic motor starters are just as robust, tolerable to voltage variations, and have some motor protection built in. They will also just snap the pump back on after a power outage, be it a blink or a long outage. The VFD is what shuts the pump down and then must be turned back on more like a computer after a power outage.
There are lots of ways VFD's on multiple pumps can be configured, which in itself is one of the problems. The easiest way to make multiple VFD's work together is simple staggering the set points. The jockey or pump #1 set at 65 PSI. Pump #2 set at 60 PSI. Pump #3 set at 55 PSI, and so on. In this way the highest pressure pump is the first to come on and the only one running until you use more water than pump #1 can supply. Then the pressure drops from 65 to 60 PSI and pump #2 starts contributing as much as needed to maintain 60 PSI. When more water is used than two pumps can keep up with the pressure falls from 60 to 55 PSI where pump #3 comes on and does what it can. This is exactly the same simple, dependable control set up we use with Cycle Stop Valves. None of the pumps are wired together in any way. If pump #2 quits, #3 just comes on to take over.
VFD's can also be wired together to do things like alternate which pumps comes on first or how many pumps are needed. Many of these systems also shut the jockey pump down when any of the larger main pumps are running.
Sometimes the biggest problem of VFD control is handling the no flow situations. There are always leaks in the system. If those leaks are less than the minimum safe flow of the pump the VFD will ramp it up and down continually. This is true even if there is a pressure tank in the system, as there is usually not enough band width to utilize much water from a tank.
A Cycle Stop Valve controlled pump can work at much lower flow rates than a VFD controlled pump. Plus, the CSV system can utilize the entire draw down of any size pressure tank as it works with a standard pressure switch. For these reasons many times a Cycle Stop Valve and pressure tank will be utilized on the jockey pump of a VFD controlled multi-pump system to solve the ramping problem. After seeing how the CSV works many people will then swap out the VFD controls on the other pumps to make the system more reliable and less expensive to maintain. However, many people never realize all their pumps could have the benefits of CSV control and just continue to replace pumps and VFD's as they cause problems or go out.
It is fascinating. Many people have careers making pump control systems as complicated and expensive as possible. Another thing I have learned in my many years of studying pumps and pump controls is this. The simpler the pumps and controls the less expensive it is to maintain and the more likely water is to come out of the faucet or sprinkler when needed.
