Well Pump with a Danfoss VLT 5000

[johnnyjb]

Good Morning,

Recently one of our good customers acquired a home up in the hills somewhere that has a pond, lots of irrigation, a home etc. Their water comes from a submersible well pump approx. 600 ft. under ground. Controlling this pump is a danfoss VLT 5000 that has not really been programmed properly so they currently use a toggle switch for start stop and it ramps to 52hz and it kind of works for them but they want to get away from using the toggle switch.

Currently I am going to install a pressure transducer so the drive can control frequency off the pressure, but my question is how and when to ramp the drive down.
Does the pump need to stay constantly running at low hz to avoid the water flowing back down and spinning the pump backwards? Or do i just ramp it to 0 when it has reached setpoint for a certain time period.

I have 0 experience with wells!

[71CHOPS]

The well should have a foot valve in the piping....Basically a check valve to keep the piping primed. So theoretically, just shut it down when not needed.

You should also be careful with your minimum HZ, and be sure the drive parameters match the motor specs. (Hp, amp draw, etc).

You'll have to determine what the system pressures "should be", and set min/max, etc.

Do they have a bladder type storage tank also?

[johnnyjb]

Okay I did not see a check valve looking device so i am going to have to check on that.

Luckily they had the motor tag left in the drive compartment and thankfully they did cause the parameters were nowhere near the motor specs.

Sounds good, yeah i will set max with all fixtures open and minimum with the smallest running. Not sure if thats the correct way but it makes the most sense to me?

They have a small bladder type expansion tank. Can't imagine it being used for storage much.

[71CHOPS]

The foot valve is in the well head casing.

Check your bladder tank pressure ratings. You'll likely just have to experiment.

You might want to get the pump curve chart to check rpm/flow rates, etc.

[johnnyjb]

Cool. Thank you for the information!

[heatingman]

Okay I did not see a check valve looking device so i am going to have to check on that.

Luckily they had the motor tag left in the drive compartment and thankfully they did cause the parameters were nowhere near the motor specs.

Sounds good, yeah i will set max with all fixtures open and minimum with the smallest running. Not sure if thats the correct way but it makes the most sense to me?

They have a small bladder type expansion tank. Can't imagine it being used for storage much.

Let max be 60 hrtz no need to derate. Pressure will dictate the speed.

For minimum you need to figure out min allowed by the pump manufacturer. If unknown safe bet would be 30 hrtz

Have the pump shut off during no flow via a pressure switch.


So lets say you want 50 psi constant

I would use an auxiliary control to act as both the pressure transducer and the set point control - could also use for start stop, but a known reliable mechanical pressure control would be a good idea.

I would use a Honeywell T775U with both a modulating output and an on/off output with compatible pressure transducer. And a square d or comparable mechanical pressure switch for a fail safe.

Set the control to 50 psi with a 5 psi throttle range to start, and fiddle from there. Set the on/off output differential to cut out at 7 above. Wont get to 7 above till you have no or low flow.

Set the mechanical pressure cut out at 15 psi above electronic control cut out.

Set the drive minimum to 30 hrtz unless pump allows less. Could also use min out function of the t775 expressed as % for this. 50 percent being 30 hertz

Set the tank pressure - empty to 2 to 3 psi below desired system pressure (disconnected from piping). This provides a cushion of water to both limit hammer at start and provides an off delay for pump restart. Bigger the tank, the more the restart delay.

The drive start/stop command would route through both the t775 on/off switch and the mechanical pressure control

If its a submersible pump, the check valve is built onto the nose of rhe pump. You wont see it, but it is there.

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