Pump + Pressure Xducer + VFD = FUN ?
Pump + Pressure Xducer + VFD = FUN ?
(OP)
I want to run a 5hp 3ph pump (230V 60Hz) at about 4hp using 1ph 230V. I also want to set it up so it maintains the water pressure at various flows at a fairly steady 70psi.
I plan to use a 0~10V pressure transducer to feed the VFD analog in. I expect to set the pressure thru button pushing up or down to reach the desired pressure. Once that's set it shouldn't be messed with.
A problem is, once all consumption stops the VFD knows nothing of this and will happily keep the water boiling at 70psi. To detect this I plan to have a check valve follow the pump. I will periodically reduce the pump speed a minuet amount and check the pressure on the down stream side of the check-valve. If the pressure doesn't drop with pump speed there cannot be any consumption occurring and I can stop the pump. If there is a pressure drop when I've slowed the pump then consumption is still occurring and I run the pump speed back up. I can do this perhaps once every 5 seconds.
I will also use a 7.5hp VFD to cover for the single phase supply.
See any problems with this grand plan?
I plan to use a 0~10V pressure transducer to feed the VFD analog in. I expect to set the pressure thru button pushing up or down to reach the desired pressure. Once that's set it shouldn't be messed with.
A problem is, once all consumption stops the VFD knows nothing of this and will happily keep the water boiling at 70psi. To detect this I plan to have a check valve follow the pump. I will periodically reduce the pump speed a minuet amount and check the pressure on the down stream side of the check-valve. If the pressure doesn't drop with pump speed there cannot be any consumption occurring and I can stop the pump. If there is a pressure drop when I've slowed the pump then consumption is still occurring and I run the pump speed back up. I can do this perhaps once every 5 seconds.
I will also use a 7.5hp VFD to cover for the single phase supply.
See any problems with this grand plan?
Keith Cress
kcress - http://www.flaminsystems.com





RE: Pump + Pressure Xducer + VFD = FUN ?
Back in the day, I saw a 60 HP pump blow a piece of cast the size of a mans hand out of the pump casing with a VFD inadvertently running at a forbidden frequency. TWICE!!!
The mechanical guys can give you more information on mitigation strategies.
Yours
Bill
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Pump + Pressure Xducer + VFD = FUN ?
1. There are many VFDs in that size range that take 230V single-phase input and give 480V three-phase output if you haven't already selected the pump motor. It sounds like you may be working with an existing installation though.
2. Bill has a very important point. Your VFD should have the ability to avoid speeds that create resonance, all you need to do is find those frequencies and program them in. We typically run the pump (or fan) speed up slowly and find them, most often with a vibration monitor. An alternative is to put a vibration transmitter on the pump and program the controller to get the speed up or down a notch when high levels are sensed. If the speeds at which this occurs are consistent over time, the controller can memorize them as forbidden.
3. There is some lower flow that is above zero, at which you must stop the pump to prevent overheating and improper lubrication (pump manufacturer will usually provide this flow rate). We typically use either a flow switch or a flow transmitter downstream and make a stop decision based on flow. With a flow switch, you can hard-wire it to the stop input on the VFD and you don't need a smart controller -- but it sounds like you already have something programmable. Your check valve may not close until the flow reaches very close to zero and becomes dangerous. If it can be set to slam at a particular flow rate, it may work. I can't remember a check valve that could function as a flow switch, though. I usually don't get into valves that aren't automated.
Good luck with it!
Best to you,
Goober Dave
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RE: Pump + Pressure Xducer + VFD = FUN ?
RE: Pump + Pressure Xducer + VFD = FUN ?
Maybe a link in the forum403: HVAC/R engineering would attract some folks with direct experience of this kind of application?
RE: Pump + Pressure Xducer + VFD = FUN ?
RE: Pump + Pressure Xducer + VFD = FUN ?
Dave; !! I don't think I've ever seen a 230 ~ 460 boost VFD. Very good point about really LOW flow support. I really wanted to avoid flow measurement.. Hmmm.
jonr12; I'm not following your logic. I don't see how setting things for the minimum flow at 70psi is going to supply 70psi at full flow?
jonr12 & LionelHutz; What is "sleep mode"?
Keith Cress
kcress - http://www.flaminsystems.com
RE: Pump + Pressure Xducer + VFD = FUN ?
An example of sleep mode: http://www.danfoss.com/NR/rdonlyres/C9AB12C2-2370-...
It is also called hibernation mode in some drives.
It basically operates in closed loop control with a sensor providing the feedback and if the VFD runs at minimum frequency for a preset period of time, it stops but is still 'alive'. It will awaken once the fb signal passes a preset point that causes the VFD to run again.
I'm not sure about the 230v 1 ph to 480v 3ph, it is probably 230v 3 ph and change the motor connection to suit the lower voltage.
RE: Pump + Pressure Xducer + VFD = FUN ?
Best to you,
Goober Dave
Haven't see the forum policies? Do so now: Forum Policies
RE: Pump + Pressure Xducer + VFD = FUN ?
RE: Pump + Pressure Xducer + VFD = FUN ?
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Pump + Pressure Xducer + VFD = FUN ?