# Wiring VFD to float switches



## varmit (Apr 19, 2009)

To maintain the tank level between two levels would only require the drive to be wired in "3 wire" control mode- the same as if it were a starter, with with a greater than low level closing the "stop" input and a high level switch closing the "run/start" command momentarily. The speed reference, in this scenario, would be a drive preset, based on trial and error, to determine the pump speed that would work for the application.

If you wanted to maintain a certain level, you would need some sort of analog transmitter wired to the drive to vary the motor/pump speed based on level or weight, for the drive speed reference.


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## MDShunk (Jan 7, 2007)

I'd probably go with a level transmitter, rather than a float switch. The level transmitter, in a tank application, would typically be a pressure transducer installed low in the tank. Analog input from the level transmitter to the VFD.


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## Cow (Jan 16, 2008)

varmit said:


> To maintain the tank level between two levels would only require the drive to be wired in "3 wire" control mode- the same as if it were a starter, with with a greater than low level closing the "stop" input and a high level switch closing the "run/start" command momentarily. The speed reference, in this scenario, would be a drive preset, based on trial and error, to determine the pump speed that would work for the application.
> 
> If you wanted to maintain a certain level, you would need some sort of analog transmitter wired to the drive to vary the motor/pump speed based on level or weight, for the drive speed reference.


I've done similar but used the floats to fire ice cube relays with a separate control power source. Then it's just a two wire input for the drive. I almost wired them the way you mentioned but I was afraid if I used the drives 24v directly, one day the floats may get damaged and I didn't want to take a chance it would short the drives 24v control power.


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## JRaef (Mar 23, 2009)

If all you have is two float switches, you are wasting your money on a VFD. Just run it across the line.

If you want a variable resonse because of the variable flow coming off the wash plant, do like Varmint said. Use a level transmitter as an analog signal to a PID loop in the VFD and set up a Set Point of the level to maintain. I've done this dozens of times on wash plant recovery tanks, it works great. Program your set point to be at the minimum level at which your pump does NOT suck air with a vortex. Then you might have to tweak the gain on the PID loop to make sure it keeps up with the maximum rate at which the walk plant flow can increase, which generally is not that fast. You will not likely need the D function in the PID loop, so don't worry about it.

A couple of words of advice. 

If you are not very familiar with using PID loops for control, get a drive that has very simple to use setup procedures and a good text display. I recommend an AB PF7x family or an ABB ACS 550, both make that really easy to implement. The cheaper the drive, the harder it will be. And stay AWAY from Schneider and Siemens drives for this, they are the WORST for setting up PID loops in my experience, even for seasoned vets.

Use an ultrasonic level transmitter, it's the most reliable for this. Make a still well out of a piece of 4" drain pipe and aim the transmitter into it to prevent having the turbulence screw you up. Good programmers can do it without the still well, but it's too much of a PITA if you ask me just to avoid a $10 piece of pipe and a couple of brackets.

Lastly, make sure your pump is capable of pumping the maximum volume at the necessary head to keep up with the maximum flow of the wash plant. Trust me, the pump guys screw this up a LOT and will ask you to "tweak the VFD output to make it pump more", which if anyone should know will not work, it should be them. But they often get excited about looking like they will save money for their user by selling them a smaller pump. The worst one I encountered was when the PID loop was pegged at maximum drive speed, the tank was still gushing over and washing away the base. I was blamed for the VFD programming, yet the motor was at full speed! Turned out they had yanked out a 400HP pump and replaced it with a 100Hp pump per the pump suppliers recommendation, then I just got the contract to supply and install the VFD. I pointed out the folly of thinking a 100HP pump could keep up, the pump guy insisted that I over speed his pump, that would take care of it. If you don't know, centrifugal pumps use power at the CUBE of the speed change, whereas the motor HP only goes up by the same ratio as the speed change. So if you run a pump at just 20% over speed, the pump power *required* goes up to 172% of the original motor rating, but yor motor is only developing 120% power, so you end up overloading it by 52%.... So to do the work of a 400HP pump, I would have had to run that small pump at something like 120Hz, which would have needed a 400HP motor. I had them put the old pump and motor back in and used a 400HP VFD, which only used the HP it needed at low flow but had the maximum capacity if they needed it. They sued the pump supplier over the additional costs, who settled out of court...


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## Go_snow (Jan 15, 2014)

Wow thanks for all the help fella's. Every one of the responses helped. I don't need a constant level on the tank, just an emergency shut off/pump start. I should be able to tweak the VFD frequency to get it close enough where the pump won't turn off often at all. 
So an easy way/cheap way to do it would be use the 24 volt out of the VFD through a side mount float http://www.gemssensors.com/Products...eered-Plastic/LS-7-Series-Type-5-Level-Switch on the top of the tank to the start side of the VFD. And then the similar float at the bottom to the stop side?
I have one more question. I will be using a very small dosing pump that will administer flocculant into the slurry pump outflow. If I would like this unit to shut off when the other VFD does, could I just Jump a line from the Start of one VFD to the start of the Other and same with the Stop? Thanks again for all the help. -AJ


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## glen1971 (Oct 10, 2012)

Go_snow said:


> I have one more question. I will be using a very small dosing pump that will administer flocculant into the slurry pump outflow. If I would like this unit to shut off when the other VFD does, could I just Jump a line from the Start of one VFD to the start of the Other and same with the Stop? Thanks again for all the help. -AJ


Use the programmable relays in the drive and drive a separate relay to stop/start other pumps as needed...Mixing controls between 2 or more drives without relays won't work...


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## wendon (Sep 27, 2010)

Why not use two floats and have the top float run at a higher speed? Maybe I'm not understanding the application.


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## Go_snow (Jan 15, 2014)

glen1971 said:


> Use the programmable relays in the drive and drive a separate relay to stop/start other pumps as needed...Mixing controls between 2 or more drives without relays won't work...


Ok. Does the first part sound correct though?


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## Go_snow (Jan 15, 2014)

glen1971 said:


> Use the programmable relays in the drive and drive a separate relay to stop/start other pumps as needed...Mixing controls between 2 or more drives without relays won't work...


Also what I meant was if another VFD receives a 24 volt monetary current, won't it start too? Meaning you have a 24 volt current going out to the float switch. When the switch closes, it sends the 24 volts back. If that line were spliced and sent one 24 volt to one VFD and one to another, it wouldn't start both?


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## sparkywannabee (Jan 29, 2013)

http://www.tesensors.com/us/products/hyde-park-sc-sm-vc-vm-xx
these are great, super easy to program both levels, should be perfect for your application.


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## Go_snow (Jan 15, 2014)

sparkywannabee said:


> http://www.tesensors.com/us/products/hyde-park-sc-sm-vc-vm-xx
> these are great, super easy to program both levels, should be perfect for your application.


Any suggestions as to which model I would need? We are dealing with about a 4 foot high to low level. I'm new to this kind of stuff so my apologies for the ignorance. I am guessing these units have a 24 volt power supply then when the water is in the high level, it closes the switch and sends 24 volts to one (Start side of VFD) and when it hits low level it closes the switch and sends 24 volts to another line (Stop of VFD). Thanks again A.J.


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## sparkywannabee (Jan 29, 2013)

You'll have to do some research and find the right sensor for your application, you can do that best since its your project, just make sure it can handle the environment its in. Also, you can run multiple pumps of the same drive, just make sure the drive HP is a little more than all the pumps combined. Signal to drive enable and signal to start, should be home free. Keep us updated.


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## erics37 (May 7, 2009)

Cow said:


> I've done similar but used the floats to fire ice cube relays with a separate control power source. Then it's just a two wire input for the drive. I almost wired them the way you mentioned but I was afraid if I used the drives 24v directly, one day the floats may get damaged and I didn't want to take a chance it would short the drives 24v control power.


While using the drive's built-in control power would work, I never do it that way. I always use the field device to switch a relay, and run the drive control through that. It adds one more point of failure, but it also isolates the drive I/O in case something down the line spazzes out. If a little ice cube relay blows out it's quick and easy to replace.


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## erics37 (May 7, 2009)

Go_snow said:


> Also what I meant was if another VFD receives a 24 volt monetary current, won't it start too? Meaning you have a 24 volt current going out to the float switch. When the switch closes, it sends the 24 volts back. If that line were spliced and sent one 24 volt to one VFD and one to another, it wouldn't start both?


I would have a separate power supply and run that through the float switch contact. That would operate a 2 or 3-pole relay or whatever, then you could route all of your drive start/stop inputs through the relay.

Your drive should also have relay output options that you can configure to actuate open or closed whenever your drive starts or stops and so forth. Use that to drive a relay, run a control circuit for the dosing pump through that.

You can wire a lot of that stuff directly to the drive, and it will probably work, I just prefer to keep the drive wiring close.


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## Go_snow (Jan 15, 2014)

erics37 said:


> While using the drive's built-in control power would work, I never do it that way. I always use the field device to switch a relay, and run the drive control through that. It adds one more point of failure, but it also isolates the drive I/O in case something down the line spazzes out. If a little ice cube relay blows out it's quick and easy to replace.


Thanks again guys. I picked up a ultrasonic pump out sensor. Basically when the water level is past the Near point, it closes a switch to one line. When the water level is pumped out and drops past the far point, it opens another line. This setup would effectively run my VFD as is. 

After hearing multiple suggestions of ice cube relays, I think I will go this route. Again, a new territory for me and I have never dealt with the actual correct wiring of an Ice cube relay. Could you possibly give me a little wiring advice on this. Sorry for my ignorance and this is greatly appreciated (I have a different profession title each day, but it allows me to always know how to fix things when they go wrong. From our concrete plant to trucks to aggregate plant, I have managed to save a lot of money and grow great knowledge doing it this way). Thanks again! A.J.


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## glen1971 (Oct 10, 2012)

Go_snow said:


> After hearing multiple suggestions of ice cube relays, I think I will go this route. Again, a new territory for me and* I have never dealt with the actual correct wiring of an Ice cube relay. Could you possibly give me a little wiring advice on this. *Sorry for my ignorance and this is greatly appreciated (I have a different profession title each day, but it allows me to always know how to fix things when they go wrong. From our concrete plant to trucks to aggregate plant, I have managed to save a lot of money and grow great knowledge doing it this way). Thanks again! A.J.


Each relay will come with a wiring diagram on the side of it.. 2 words of advice.. Don't go with the cheapest one on the market - you get what you pay for... Also don't find a "great deal" on one and end up with the only one in the county.. Find something that is common in your plant/supply houses...


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## sparkywannabee (Jan 29, 2013)

If you really want to make this a fun learning project, build a panel, add a Micrologix1000 plc, if you have RSlogix software, else i think AB makes a low end plc that comes with free software. Add a couple of motor starters in your panel and wire the coils to your plc outputs, your sensor signals to your inputs. This way you can add or modify in the future, no need to use any 60's relay technology. Maybe JRaef will get you an employee discount if you ask him nicely.


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## JRaef (Mar 23, 2009)

Go_snow said:


> Thanks again guys. I picked up a ultrasonic pump out sensor. Basically when the water level is past the Near point, it closes a switch to one line. When the water level is pumped out and drops past the far point, it opens another line. This setup would effectively run my VFD as is.
> ...


I still don't get the need for a VFD here.


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## oliquir (Jan 13, 2011)

sparkywannabee said:


> If you really want to make this a fun learning project, build a panel, add a Micrologix1000 plc, if you have RSlogix software, else i think AB makes a low end plc that comes with free software. Add a couple of motor starters in your panel and wire the coils to your plc outputs, your sensor signals to your inputs. This way you can add or modify in the future, no need to use any 60's relay technology. Maybe JRaef will get you an employee discount if you ask him nicely.


ab plc are the most expensive plc, just get a click plc or teco smart relay they are some models under 100$ all with free software


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## sparkywannabee (Jan 29, 2013)

JRaef said:


> I still don't get the need for a VFD here.


I think he wants to choke pump output by lowering motor frequency, probably should use VFD rated motor, regular motor might be ok if it runs for a shorter duration or if its a submersible deal. If nothing else a VFD will provide soft start and stop.


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## JRaef (Mar 23, 2009)

oliquir said:


> ab plc are the most expensive plc, just get a click plc or teco smart relay they are some models under 100$ all with free software


As is the Micro 810 ($85 LIST) which is of equal capability, and the software is free too.


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## Go_snow (Jan 15, 2014)

JRaef said:


> I still don't get the need for a VFD here.


Because I have a 600 GPM Slurry pump that will be fed off of a 600 gallon tank. The amount of wash water will vary depending on the time of the year and there is no need to pump at 600 GPM for 1 minute only to turn the pump off and fill all the way again. Instead with a VFD I will be adjusting the speed depending on the output and only have the pump turn off once or twice throughout the day instead of every other minute. Also, multiple starts and stops is hard on a motor instead of running slowly all day.


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## varmit (Apr 19, 2009)

JRaef said:


> I still don't get the need for a VFD here.


I think that he sets the drive/motor speed by guesstimation to try to maintain some average level in the tank.


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## Go_snow (Jan 15, 2014)

varmit said:


> I think that he sets the drive/motor speed by guesstimation to try to maintain some average level in the tank.


Yep! Also when the need for water increases (dry season), I can change the VFD. I need safety shutoff's for the decrease in water when the plant has no material running through it (water flow to tank decreases greatly as displacement from material isn't there). This is what the shutoff and start are for. 

On another note, I'm new to these Logic Controllers. Can someone tell me if I'm understanding these correctly? Basically you have a 24 Volt power supply to the Logic controller (say the 810). A terminal receives a 24 Volt signal on the 810 and you tell it what other terminals you want it to open and send 24 volts out of ?


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## rick480volt (Aug 23, 2011)

We set our rock quarry pumps on a timer in the winter for 1 hour on and 3 off. In the warmer months we have a 3 float system, figure it out with 2 pumps. And we raise the floats in the winter. Our floats sit in an aluminum pole that we can raise or lower if need be.
I don't see any reason to have a VFD on a pump motor.


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## sparkywannabee (Jan 29, 2013)

oliquir said:


> ab plc are the most expensive plc, just get a click plc or teco smart relay they are some models under 100$ all with free software


Anytime somebody else is paying for it, you always buy AB.


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## sparkywannabee (Jan 29, 2013)

Go_snow said:


> Because I have a 600 GPM Slurry pump that will be fed off of a 600 gallon tank. The amount of wash water will vary depending on the time of the year and there is no need to pump at 600 GPM for 1 minute only to turn the pump off and fill all the way again. Instead with a VFD I will be adjusting the speed depending on the output and only have the pump turn off once or twice throughout the day instead of every other minute. Also, multiple starts and stops is hard on a motor instead of running slowly all day.


600GPM on a 2 HP motor, thats a pretty healthy pump, are you sure about your numbers.


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## Go_snow (Jan 15, 2014)

sparkywannabee said:


> 600GPM on a 2 HP motor, thats a pretty healthy pump, are you sure about your numbers.


Dosing pump is 2 hp and run off one vfd. 5x5x14 rubber lined slurry pump is 15 hp run off another vfd. Sorry for the confusion! I wish I could find a 2hp 600 gpm pump!


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## Go_snow (Jan 15, 2014)

And this project is for my company. So money is very important and one of the reasons I am taking the time to do the entire project instead of hiring out


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## Jack30802 (Jul 6, 2013)

Turk has a easy controller relay size probe system works great


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## oliquir (Jan 13, 2011)

if you want to maintain level just buy an analog ultrasonic level and adjust setpoint in vfd and vfd will automatically adjust output frequency 
(just use pid function in vfd) . a lot easier than floats with plc or relays...
ive done this a lot of time with tanks


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## Go_snow (Jan 15, 2014)

oliquir said:


> if you want to maintain level just buy an analog ultrasonic level and adjust setpoint in vfd and vfd will automatically adjust output frequency
> (just use pid function in vfd) . a lot easier than floats with plc or relays...
> ive done this a lot of time with tanks


After much thought, I've decided to go this Route. What ultrasonic level would you suggest? Also I will be wiring this to a Altivar VFD so hopefully that won't give me too much nightmare. Thanks


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## oliquir (Jan 13, 2011)

i have sucessfully used those cheap ones with 4-20ma output for water level
http://www.automationdirect.com/adc...m_Maximum_Sensing_Distance_(UK_-z-_SU_Series)

it depend on your tank size for exact model


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## Go_snow (Jan 15, 2014)

oliquir said:


> i have sucessfully used those cheap ones with 4-20ma output for water level
> http://www.automationdirect.com/adc...m_Maximum_Sensing_Distance_(UK_-z-_SU_Series)
> 
> it depend on your tank size for exact model


Sorry to keep bugging you on this. Being my PID experience I'm struggling. I have a 4 foot tall water tank. I called and talked with tech service and they directed me to the Liquid Level Sensing (more like 400 dollars). Could you point me in the direction of the one you would use given I only am dealing with a 4 foot tall tank (1 foot is not useable as the pump would cavitate). Thanks in advance!


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## Jlarson (Jun 28, 2009)

Take a look at Flowlines EchoPod sensors. In fact automation direct just started to sell them, makes them a lot easier to get a hold of. :thumbsup:


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## Jlarson (Jun 28, 2009)

Stay away from the Altivar (Alticrap) drives if this is your first time too, actually just stay away from them all together.


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## oliquir (Jan 13, 2011)

i use automation direct gs3 drive also. i think it is the easiest pid setup ive seen


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## Go_snow (Jan 15, 2014)

I think I'll be putting the altivar away for storage and using it for some non PID related process. So any other suggestions on VFD's for easy PID setup? Also oliquir, could you help me in figuring out what sensor I need for a 4 ft tall water holding tank. Thanks


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## oliquir (Jan 13, 2011)

the ones i listed before ( UK1D-E2 ) are ok up to 64 inch, there are also Flowline EchoPod dl10-00 wich are 4.1ft max but you also need usb adapter to program it.
i would try the uk1d-e2 and if it doesn't work well then you can return it or use it elsewhere


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## Go_snow (Jan 15, 2014)

oliquir said:


> the ones i listed before ( UK1D-E2 ) are ok up to 64 inch, there are also Flowline EchoPod dl10-00 wich are 4.1ft max but you also need usb adapter to program it.
> i would try the uk1d-e2 and if it doesn't work well then you can return it or use it elsewhere


Wonderful. That should work great. Another question as it sounds like you've been around this kind of thing before. Have you ever run across a sensor that can send a 4-20ma signal regarding the percent of solids in liquid? Basically the outflow from the pump will be floculated. It would be incredible if I could have a sensor that could measure suspended solids and then adjust flocculant pump rate via a VFD. Thanks fellas


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## kreddad (Oct 24, 2013)

sparkywannabee said:


> I think he wants to choke pump output by lowering motor frequency, probably should use VFD rated motor, regular motor might be ok if it runs for a shorter duration or if its a submersible deal. If nothing else a VFD will provide soft start and stop.


so in the cas just use softstarter. cost less $$$$$$


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## DIRT27 (Aug 25, 2010)

Go_snow said:


> Wonderful. That should work great. Another question as it sounds like you've been around this kind of thing before. Have you ever run across a sensor that can send a 4-20ma signal regarding the percent of solids in liquid? Basically the outflow from the pump will be floculated. It would be incredible if I could have a sensor that could measure suspended solids and then adjust flocculant pump rate via a VFD. Thanks fellas


Where I work we have a sludge transfer pump that we use a pressure transmitter on the output of the pump to determine the thickness of the sludge. It has a glycol filled doughnut that bolts to a pipe flange so the transmitter does not get plugged. The thicker the sludge the more pressure is applied to the transmitter. Something like this may work for your application, but when setting something like this in auto you may get in a situation where you are wasting flocculant because there are not enough solids to get the desire pressure. 

It is hard for me to understand the whole scope of the project and what your exact needs are. It looks like you could do a 2 speed motor starter or a lead and lag pump with 2 float switches. I would try to find someone that could help you design the process and understand you needs. 

The VFD setup would work if you need to try to keep the tank as close as possible to set point. I have never tuned a loop with a VFD in a stand alone system like you are describing, but I agree you do not need the derivative in the PID for your application. Let us know what you go with and how it works out.

I am interested in learning more about tuning the PID loop in this application. I have messed loops on a DCS system where you put the loop in manual make a change and measure results to get starting points, then fine tune from there. Is it similar with this set up where you need set up a labtop and track the level in the tank and adjust there?


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## Go_snow (Jan 15, 2014)

Just wanted to update my project status. Bought a used ACS500 15 hp vfd and an ultrasonic sensor 4 to 20 mA. I will be using the pfc setup of the VFD drive to control the level of the output. I wanted to make sure my wiring was correct for my 3 wire sensor so if anyone could confirm that would be great.
-(10) 24+ VDC to + of sensor
-(6) Analog common ground to - of sensor
-(5) AI2 PID input 4...20 to 4.....20 output of sensor.
-Jumper between (6) AGND and (11) GND
Also thinking of running a very small flocculant motor off of the same VFD that will mimic the large slurry pump. As the flow rate of pump increases due to PFC control, so will the flocculant pump rate (Install short circuit and overload protection). good idea?? Thanks, AJ


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