5 replies to this topic

[chrisp]

hi marke

[chrisp]

hi marke

question regards VSD

question regards VSD

sorry this posting giving probs am canterbury farmer possible to ring you?

[marke]

Hello chrisp

Yes, no problem,
Phone number is new zealand 0274 363 067 Before 11PM or after 8AM should be OK.

Best regards,
Mark.

[chrisp]

Hello chrisp

Yes, no problem,
Phone number is new zealand 0274 363 067 Before 11PM or after 8AM should be OK.

Best regards,
Mark.

cheers...wrote out a long question only to have it disapear will try this again otherwise will ring next week

cheers...wrote out a long question only to have it disapear will try this again otherwise will ring next week

ok here goes,
would like advice on best tank fill practice
Have 230kw pump/motor danfoss VSD
I fill mainline pump goes sleep at 400kpa takes 30 min to lower to 100kpa pump ramps up 30hrtz ,pressurises mainline again then goes sleep.does this for 30hrs till house tank fills via 3/4 alkathene off last hydrant
Could i be damaging pump/motor?

[marke]

Hi Chrisp

Got it through OK this time!!

The problem that you will have is that the flow rate through the 3/4 alkathene pipe will be very low relative to the pump capacity that there is probably little else that you can do in reality.
Iassume that there is a ball *beep* in the tank on the end of the alkathene pipe and this is controlling the flow into the tank.

In terms of damaging the pump and the motor, my first comment is that you will not be damaging the drive, so take that out of the equation, but it is important that with submersible pumps, (I assume that thsi is a submersible) that you must operate the pump such that it is actually pumping. If you run the pump at too low a speed, you wil damage the seals and possibly bearings.
The normal recommendation is that the pump must get up to "pumping speed" in less than two seconds.
The motor should not be adversly affected by this operation provided that there is plenty of cooling for the motor.

If the minimum speed setting of the drive was too low, it would not be up to pressure within the pump and leakage could occur. If the drive is reliably going to sleep, then I would assume that the minimum speed is high enough to "pump".
My suggestion would be to ensure that the sleep delay is kept to a minimum so that the time operating at minimum speed is restricted.
I would suggest that a 3 second sleep delay would be as high as I would go unless there was some other issue that caused other problems.
My other concern is the time taken to accelerate from zero speed and the time taken to decellerate from minimum speed back to zero speed. These accel and decell times betwen zero and minimum speed should be less than 2 seconds, especially as this unit will be doing a lot of cycles during the tank fill period. (once again, assuming a submersible pump!)

While this is not an ideal situation from the pumps perspecitve, it is commonly done. If you are concerned, I would contact the pump supplier and get their input also.

Best regards,
Mark.

[chrisp]

Hi Chrisp

Got it through OK this time!!

The problem that you will have is that the flow rate through the 3/4 alkathene pipe will be very low relative to the pump capacity that there is probably little else that you can do in reality.
Iassume that there is a ball *beep* in the tank on the end of the alkathene pipe and this is controlling the flow into the tank.

In terms of damaging the pump and the motor, my first comment is that you will not be damaging the drive, so take that out of the equation, but it is important that with submersible pumps, (I assume that thsi is a submersible) that you must operate the pump such that it is actually pumping. If you run the pump at too low a speed, you wil damage the seals and possibly bearings.
The normal recommendation is that the pump must get up to "pumping speed" in less than two seconds.
The motor should not be adversly affected by this operation provided that there is plenty of cooling for the motor.

If the minimum speed setting of the drive was too low, it would not be up to pressure within the pump and leakage could occur. If the drive is reliably going to sleep, then I would assume that the minimum speed is high enough to "pump".
My suggestion would be to ensure that the sleep delay is kept to a minimum so that the time operating at minimum speed is restricted.
I would suggest that a 3 second sleep delay would be as high as I would go unless there was some other issue that caused other problems.
My other concern is the time taken to accelerate from zero speed and the time taken to decellerate from minimum speed back to zero speed. These accel and decell times betwen zero and minimum speed should be less than 2 seconds, especially as this unit will be doing a lot of cycles during the tank fill period. (once again, assuming a submersible pump!)

While this is not an ideal situation from the pumps perspecitve, it is commonly done. If you are concerned, I would contact the pump supplier and get their input also.

Best regards,
Mark.

cheers Marke will ring you about this