Ag Irrigation pump work

[avocadofarmer]

Howdy,

Great forum here...lots of things I should know more about.

I'm currently in the midst of a project here on the farm.  I've currently got a well that sits about 200 feet in a valley below my farm.  I pump from this well with a 40HP motor on a VFD up to the trees at a rate of about 150 GPM @170 PSI.  For lots of reasons, I'm having a big tank installed at the top of the property that I will use as storage and also for ease of irrigation management.  As luck would have it, there are nearly 200 trees around this tank that are irrigated with micro sprinklers (.16 GPM each) that will not have sufficient head pressure from the elevation difference of the tank.  For these trees, I will need a booster pump.  Something in the 40 GPM / 40 PSI range.

I spoke with my well driller/pump guys and they admitted that the smallest pump setup they deal with would be overkill for this small of a flow, but it could be done.  This is would be a 'wet well' on a 3 Phase VFD.  Talked about other options, but they really like the wet well pumps due in no small part to their significantly longer warranty period vs above ground pumps.  Total estimated bill, $6k.  I've been looking around trying to find another way.  Looked at Grundfos CM / CME pumps.  Even the CME with the VFD setup was 2500 or so, which looked a whole lot better than $6K.  Even better still is the Grundfos CM-10.  Really simple pump that I think just turns itself on and off with a pressure switch.  Which brings me to this site and my question...If I have my tank plumbed directly to the pump plumbed to a Hunter irrigation control valve, would I be served well with a CSV?  I anticipate controlling this irrigation block by simply directing the hunter sprinkler valve to open, having the pump turn on and then shutting the valve when the time is up.  Is this a decent and practical way of doing this? 

What are your thoughts about the CM pump? 

Thanks in advance...

Matt 

[Cary Austin]

Hi Matt
Sorry you have already fallen for the VFD hype.  You spent way more than was needed for that 40HP and the VFD.  Anytime you lower the speed of that pump, you are using more energy per gallon of water produced, no matter what they tell you about a VFD saving energy.  When you start having problems with that VFD you can easily switch it out and start using a CSV.  The CSV will lower the amp draw of the motor almost exactly the same as the VFD.  But the CSV will cost much less, and make the pump last many times longer than when controlled by a VFD.

The same thing applies for the 40 GPM pump you need.  A VFD will just be expensive and a complete waste of your money.  VFD's are designed to make you think they are saving energy, so you won't mind the added expense up front and the frequent expenses keeping the pump and controls working.

If you are running these zones from a sprinkler clock, you don't need any kind of control.  You can use a pump like the Goulds Gator GT15, which I see for $277.  The sprinkler clock will turn on the pump when the zone valves open, and turns off the pump the same time it closes the zone valves.  This would be simple, inexpensive, energy efficient, and will last a long time.  You can use this pump like this for zones up to 40 GPM and down to as little as about 1 GPM.  But the same as with a VFD, the closer you use the pump to its design point of 40 GPM, the more water you get per kilowatt.

If you don't have a sprinkler clock and/or want the pump to start when you open a garden hose, then a small pressure tank, pressure switch, and a CSV will make it all automatic for you.  You would need to use a pump with a little more head available than the Gator to work with a pressure switch.

You can also put a submersible pump in the storage tank if you wish.  Something like the Grundfos 40S15-5 would work very well.  Then you can make this pump vary the flow and come on and off automatically like with a VFD, by simply using a CSV with a small pressure tank and a pressure switch.  I see these pumps on the internet for about $1,000.  Then the CSV12540-1 would cost you about 63 bucks, a pressure switch maybe 15, and a 20 gallon size pressure tank about $100.  This would be much less expensive than any VFD, would make the pump last longer than with a VFD, would vary the flow rate as needed like a VFD, and save just as much energy as a VFD.

But if you are listening to the pump guys, they are going to sell you what they make the most money on and doesn't last very long.  That way they get to sell you another one very soon.

If you do this the right way with a CSV, you should never have to spend another dime on your pump systems.  And I am afraid your pump guys know this already, so guess what they are going to tell you? 

[avocadofarmer]

Hi Cary,

Thank you for the informational reply.  So these pumps have some sort of internal pressure sensor turns the pump on or off depending on the position of the downstream sprinkler valve?  Also, would a Grundfos CM10-1 in 3 phase be better/more efficient than the gator?  I've got 3 phase power (that I have pulled 1500 ft!!) so I think a 3 phase pump would be more efficient?  Due to the length of the pull, wire size is also important...I need to keep an eye on amps. (no more than 10a on a 3 phase, not sure how many amps would be lost in a step down transformer)

Seeing as how the flow of this irrigation block will never vary, I can understand why a VFD is totally unnecessary.  I'm still trying to figure out how I would get by without it on my big pump though.  By adjusting the Hz I can get the pressure to exactly where I need it without over pressurizing the system and (I assume?) wasting energy. 

I'm going to be drilling another well in a few months and I can imagine the well drillers will want to use another VFD.  This project will be slightly different, however, in the sense that this well will only be used to fill a 30,000 gal storage tank.  I can see how it would be best to just pump at one set rate into this tank instead of having all of the complicatedness of a VFD.  Does the soft start/stop and other pump saving computer tricks that come with a VFD make it useful?  Better to use the smallest wire available down the borehole to cause startup voltage drop as a soft start mechanism?

In regards to my existing VFD setup...I had this well installed in 2012 and have already replaced TWO VFD controllers.  All of the sudden they make a big scary sound when I turn the power on and blow all of the fuses.  Only solution is to replace the whole thing.  Luckily they've been under warranty.   

Thanks for the help, this has definitely changed my mind about the almighty VFD!

[Cary Austin]

Thank you for the informational reply.  So these pumps have some sort of internal pressure sensor turns the pump on or off depending on the position of the downstream sprinkler valve?  Also, would a Grundfos CM10-1 in 3 phase be better/more efficient than the gator?  I've got 3 phase power (that I have pulled 1500 ft!!) so I think a 3 phase pump would be more efficient?  Due to the length of the pull, wire size is also important...I need to keep an eye on amps. (no more than 10a on a 3 phase, not sure how many amps would be lost in a step down transformer)

Stay away from anything that has an “internal pressure sensor or VFD”.  You can get the Gator in 3 phase as well.  It will even be a little less expensive.  You just need to use a regular contactor type starter instead of a VFD.  3 phase motors are a little bit more efficient, but not very much.   However, in your case the smaller wire size is a bonus with the 3 phase motor.

Seeing as how the flow of this irrigation block will never vary, I can understand why a VFD is totally unnecessary.  I'm still trying to figure out how I would get by without it on my big pump though.  By adjusting the Hz I can get the pressure to exactly where I need it without over pressurizing the system and (I assume?) wasting energy. 

Anytime you vary the speed below 60 hertz with a VFD, you are spending more on electricity per gallon pumped.  But sometimes varying the flow can be beneficial enough to the system that the added power cost is worth it.  What many people do not understand is that the amps or power consumption of the pump will drop almost exactly the same way by simply restricting the pumps flow with a valve.  The CSV will hold a steady set pressure just like a VFD, and the amps will still drop like with a VFD, even though the RPM of the pump never changes.  With a CSV you would just be using a simple, inexpensive, long-lasting, mechanical valve, instead of a complicated, expensive, short-lived, computerized VFD.  The pressure will stay exactly where you need it by simply adjusting the one adjustment bolt on the CSV.  The pressure adjustment of the CSV you need is from 15 to 150 PSI.  If you set the CSV to hold say 80 PSI, the CSV will hold a steady 80 PSI no matter if the flow required is a little or a lot.

I'm going to be drilling another well in a few months and I can imagine the well drillers will want to use another VFD.  This project will be slightly different, however, in the sense that this well will only be used to fill a 30,000 gal storage tank.  I can see how it would be best to just pump at one set rate into this tank instead of having all of the complicatedness of a VFD.  Does the soft start/stop and other pump saving computer tricks that come with a VFD make it useful?  Better to use the smallest wire available down the borehole to cause startup voltage drop as a soft start mechanism?

I see you have already read that using the longest length of the smallest possible size wire will act like a soft starter.  It does a good job without any added expense.   But also a CSV makes the pump start and stop at 5 GPM.  This gives a mechanical soft start and soft stop to the pump system.  Starting the pump against an almost closed CSV gives the same reduced amps and torque as with a VFD. 

A VFD accomplishes soft start in a different way.  The VFD slowly ramps up the speed of the pump to produce a soft start.  The bearings in a submersible pump and motor are water lubricated.  It takes a certain minimum RPM to produce the water to lubricate the bearings.  The longer you slowly ramp up the speed of the pump, the longer these bearing run in a dry, un-lubricated condition.   And as you said there really is no need to vary the pump speed when you are simply filling a storage tank.

Besides the mechanical soft start/soft stop of the CSV, which eliminates water hammer, automatic operation is another good reason to use a CSV, even when just filling a storage tank.  With the CSV, small pressure tank, and a pressure switch, you can simply open a valve at the storage tank, and the pump will automatically start and fill the tank.  Then when you shut the valve at the storage tank, the CSV will let the little pressure tank slowly refill, and the pressure switch will automatically shut off the pump.  This way the storage tank can be as far away from the pump as needed, and no wires or radios are needed to send a signal to the pump to start and/or stop.

In regards to my existing VFD setup...I had this well installed in 2012 and have already replaced TWO VFD controllers.  All of the sudden they make a big scary sound when I turn the power on and blow all of the fuses.  Only solution is to replace the whole thing.  Luckily they've been under warranty.

Yeah you are lucky they have been under warranty.  But make no mistake about it, the first time the VFD quits after the warranty is out, they will make back enough money from you to cover the warranty replacements and then some.  This is the story I hear everyday.  In their infinite wisdom, many utility companies and some government agencies are paying incentives for people to install VFD’s.   They want you to think they are helping the American public save energy.  However, after the warranty is out, you will be paying more to keep a VFD working than you would ever save in energy costs, especially since there are no energy savings.  There is no repair of a VFD.  The only solution is to keep replacing them as they go out.  If these utilities are not getting kick-backs under the table from the VFD manufacturers, which I think they are, then they should be.  This is one of the biggest hoaxes being played on the American people today.

Thanks for the help, this has definitely changed my mind about the almighty VFD!

You would think slowing the RPM of a pump with a VFD would reduce the energy consumption, but it actually increases energy use.  You would also think restricting the output of a full speed pump with a valve would make the pumps work harder, which is the opposite of the truth.  Using a VFD to slow the RPM of a pump actually uses more energy and shortens the life of a pump/motor.  Using a CSV to restrict the output of a pump reduces the amp draw of a motor the same as reducing the RPM.  However, the CSV will extend the life of the pump/motor, and there are no short-lived and expensive electronics to be continually replacing.  Both of these things are counter intuitive, which is why it is hard to comprehend, and also makes it easy for VFD manufacturers to pull the wool over our eyes.

When the VFD on your 40HP goes out again, get a regular magnetic starter and a CSV.   Then the next time you have a problem with this pump your descendents can worry about it, because you and I will have been dead and gone for a long time.

[avocadofarmer]

Wow, thanks for the info! 

Oddly enough, I have another well that was put in place by the same well drillers and I believe they used a CSV at that location.  The well is smaller, but there is a 5gal pressure tank at the head and I turn it on just by opening the valve.  I've always wondered how important it is to open/close that valve really, really slow?   

On my other well (40 HP and VFD) I need about 170 PSI at the well head to move water up the hill and into my storage tank.  If I turn the VFD up to 60 Hz the pump will extract nearly 200 GPM from the well (3" well manifold, 4" main line going the distance).  Is there a CSV large enough to handle this flow and pressure? 

It seems to me that choking down the pressure at the well head to reduce the flow would cause a large spike in pressure between the pump and the 'choking down' point, but from reading what you've written and other things I am going to reconsider!

Thank you for the helpful and money saving information!  Next time my VFD fails I'm going to change course.

[Cary Austin]

  Oddly enough, I have another well that was put in place by the same well drillers and I believe they used a CSV at that location.  The well is smaller, but there is a 5gal pressure tank at the head and I turn it on just by opening the valve.  I've always wondered how important it is to open/close that valve really, really slow?

I heard the same thing from city in Georgia a few years ago.  They had a bunch of wells feeding an island community.  Most of the wells had VFD controls on them.  They had replaced those VFD’s so often they had no problem showing my salesman to every location.  But there were about 5 wells they could not find.  Turns out those 5 wells had been controlled with CSV’s for as long as the others had been on VFD’s.  The 5 wells with CSV’s had never given a problem, so in all these years no one had even been back to the locations.  When they finally found those 5 wells, they were still running fine with the CSV controls.  Sure made it easy to talk them into replacing about 50 VFD’s on that well field. 

  On my other well (40 HP and VFD) I need about 170 PSI at the well head to move water up the hill and into my storage tank.  If I turn the VFD up to 60 Hz the pump will extract nearly 200 GPM from the well (3" well manifold, 4" main line going the distance).  Is there a CSV large enough to handle this flow and pressure? 

A 200 GPM pump only needs a 3” CSV.  The standard B series CSV comes standard with a 15 to 150 pressure adjustment. ($1,078 your cost)  But it can be easily be adapted with a different spring for adjustment from 150 to 300 PSI. ($1,284.50 your cost) We also have a 3” valve in the R series that can handle pump pressures up to 720 PSI. ($1,767.50 your cost)

The problem with these high pressures is needing a small pressure tank rated for 175 PSI or higher.  But even one of these high pressure little tanks would only cost you about $3,000.  Add to that a high pressure switch for about 300 bucks, and the 170 PSI pump you have now can have CSV controls for automatic operation for less than $5,000.  I’ll bet the VFD cost a lot more than that.

  It seems to me that choking down the pressure at the well head to reduce the flow would cause a large spike in pressure between the pump and the 'choking down' point, but from reading what you've written and other things I am going to reconsider!

The CSV does cause higher pressure on the pipes before the CSV.  That is how it works.  It makes the pump think it is in a deeper well, so it produces less flow when needed.  I am guessing a pump that operates at 170 PSI will probably have backpressure before the CSV of maybe 250 PSI.  But that 250 PSI should only be seen on a 6” long nipple between the pump and the CSV.  Everything after the CSV will be held at a steady 170 PSI.

I have some CSV's in North Carolina that operate at 400 PSI.

  Thank you for the helpful and money saving information!  Next time my VFD fails I'm going to change course.

You will be glad you did.  Let me know if you have more questions.

[Cary Austin]

  Oddly enough, I have another well that was put in place by the same well drillers and I believe they used a CSV at that location.  The well is smaller, but there is a 5gal pressure tank at the head and I turn it on just by opening the valve.  I've always wondered how important it is to open/close that valve really, really slow?

I forgot to answer this one.  The valve at the storage tank can be opened or closed fairly quickly.  The CSV reacts very fast and will open or close as fast as you open or close the valve at the storage tank.  However, you have to give the CSV a second or two to react.  So if you slam a ¼ turn ball valve as fast as you can you will get ahead of the CSV and the pump will bounce on and off.  Just give yourself a count of 2 when you close the valve and the CSV will be easily able to keep up.  If you have a gate valve instead, you can spin it as fast as you want and you can never get ahead of the CSV.