Recommendations for a VFD controlled by water table on well pump against 130 psi head

I'v got a 3/4" sounding tube down a 147 ft. well with a 4" submersible 5 hp 230v Franklin 3ph multistage pump. Finally found a pressure transducer that will go down the tube. I want to control the pump with a VFD that is controlled by the drop in the water table. Has anyone any recommendations? What is your opinion about slowing that pump down against a 130 psi head? We have to pump uphill to two 10,00 gallon open tanks.

Paul

Both the Yaskawa and Hitachi drives have this ability. I dont think the Franklin, grundfos, or Pentek drives have this ability. Both brand H and Y can be set up to run to meet demand up to full flow, until the well draws down to a specified level and then pump no more than what will maintain that water level in the well.

A couple of weeks ago, I set up a Hitachi running a 10 hp sump pump in a wet well. Instead of the float switch turning the pump on and off, it speeds the pump up or slows it down. We're using a $25 float switch instead of a $500 submersible pressure transducer. One supplier quoted me $4300 for a VFD in an outdoor enclosure with a submersible pressure transducer. We installed the Hitachi in the customers existing enclosure and used the existing float switch, turning the pump into a two speed pump. No starting torque either. My cost for materials was under $800.

You can do what you are asking, and as long as you have minimum flow, it won't hurt the pump at all......but it's really an overcomplicated system for what you are doing.

What is the yield of the well? How much water do you use from the storage tanks...in gallons per day?

You could save yourself a lot of money, energy and headaches if you just get the right pump for the job.

They have been doing that in sump pits for sewage pumps for a long time. Many people have tried it on irrigation wells in my area without much success. When a well pumps down, the water cascading down from the upper perforations gives an erroneous signal to the transducer.

You also have to set the minimum speed of the pump to maintain the minimum flow needed to cool the motor. If the minimum flow to cool the motor is more than the well can produce, then the well will still be pumped dry.

This can also be done using a Cycle Sensor to control a standard full speed pump. The Cycle Sensor looks for amp draw and is sensitive enough to detect a low pumping level. At low level and low amps, the Cycle Sensor shuts the pump off, then it can be set to restart the pump from 1 to 500 minutes after the well has recuperated.

High and low probes in the well also work very well.

It would be best to choose a pump that is matched to the maximum output of the well. But if the pump is oversized, a simple ball valve can throttle the pump to match the well output.

Thanks for the reply. Do you know of a a small float switch/water sensor that will go down my 3/4" PVC tobe?

BW Controls make the simplest and more reliable liquid level controls in my opinion....the electrodes MIGHT fit in your tube.....the aren't heavy, and I would worry the wire would cling to the side of the inside of the pipe. The normal method would be to tape them to the drop pipe during the pump install. Did you have any idea as to your water usage? Probably can do a lot better on price, but look at http://www.deanbennett.com/bw-lh-systems.htm

Thanks for all the help from you guys. I tried to talk the owner into a soft start system only but someone got him excited about VFD's. I was worried about the Minimum Stable Continuous Flow all along. He might want to try the complicated way as an experiment.
I'll let you know how it works out.
Paul

By the way, we have already down-sized the pump from a 7 1/2 hp one that was in there at first. Yes. It might be a good idea to go smaller. We used to pump in the high 20 GPM range and now we run at 17GPM.

Paul

Well a 3HP, 18GS30 would pump exactly 17 GPM from 147’ and 130 PSI. You can even put a 3HP pump end on the existing 5 HP motor. The only problem is you probably have single-phase power, and the VFD is converting single phase to three phase, because the VFD needs a three phase motor to work with. This is also how they lock you into keeping the VFD, even after you have decided you don’t need or want it, because without the VFD you would have to purchase a new single-phase motor.

No more often than a cistern fill pump will be cycling on and off, a soft starter is not at all necessary. And if it you want a soft start anyway, using the longest length of the smallest wire recommend works like a resistor, which makes a soft starter by limiting the starting current and torque. With a 3HP single-phase set at 147’, using 190’ of #12 wire makes a good soft starter all by itself.

BTW the minimum cooling flow required for a 5HP motor in 6” casing is 13 GPM. So a VFD is limited in that it can only vary the flow from 17 to 13 GPM. But varying the flow is not needed if the well makes 17 GPM, the pump needs to produce 17 GPM. Give me the model number for the pump you have, and I can tell you the maximum hertz or speed to set it at so it can only produce 17 GPM. Then you won’t need a transducer at all, just a float switch in the cistern to turn the pump on and off as needed.

If you have even one more problem with the VFD pump system, you would be better off cutting your losses now by changing out the system to a 3HP with a standard single phase control box. The VFD is doing absolutely no good in this application, and is turning your well into a 147’ deep money pit.