Which Grundfos pump?

[ian morrison]

I am replacing a 2 hp McDonald deep well pump. It's a vineyard irrigation pump and has provided reliable irrigation water for years but is starting to go. I'm planning on replacing it with something similar. I'm looking at Grundfos pumps and would like to get some opinions on the SQ series as compared to the SP series. If I'm reading the charts correctly I can get as much water at about the same pressure from a 11/2 hp SQ pump as from a 2 hp SP pump. The two I'm considering are the:

Grundfos 51530115, Model 25s20-11, 25s-SP Series, 4" Multistage Submersible Well Pump (Complete with Pump, Motor and Motor Lead), 2 HP, 230 Volts

Grundfos 96160152, Model 15SQ15-290, SQ Series, 3" Submersible Well Pump, 1-1/2 HP, 240 Volts.

Would a 3-phase pump be advisable for the SP?


Thanks in advance

 

[Valveman]

Need to know the pumping depth and pressure you want? But the 15SQ is not similar to the 25S20-11. The 22SQ15-330 is much closer to the 25S20-11. The SQ pumps are tiny and spin 10,700 RPM to do the same job as the larger 3,450 RPM 25S20-11. Kind of like the difference between a fast spinning Drimel tool and a slow spinning heavy duty bench grinder. As per Grundfos' engineering manual, doubling the RPM will quadruple the wear rate. So, the 25S20-11 should last longer. I have one that is 30 years old and still working. However, mine is controlled with a Cycle Stop Valve, which makes pumps last several times longer than normal.

NO, you do not want a 3 phase motor. That would mean you would need a VFD to convert your single phase power to three phase to make that motor work. The Cycle Stop Valve does a better job than a VFD and works with normal single phase motors. The Cycle Stop Valve is made to replace VFD's and has been doing so for 30 years. If you want something complicated, expensive, and short lived get a three phase motor and a VFD. If you just want water to dependably come out of your faucets for decades, get a single phase motor and a CSV.

 

[ian morrison]

Thanks for the response. I was concerned about the 10,000 rpm on the SQ. I'm going to need more help in figuring all this out. Here is my situation:

The well is used exclusively to water a 4-acre vineyard divided into 5 blocks of 500 vines each. I need ~12 gal/min to provide water to each vine some of which are 10-50 feet above the level of the well. The 2 hp pump sits at 85 feet in a 200 foot 8" inch well that was drilled in 1975. I have the well log and it tested at 50 gal/min at 100 feet. It is a simple system controlled by a standard pressure gauge set at 55 to 75 psi and uses a 350 well-x-trol pressure tank. I believe the pump is undersized because most of the time it runs constantly when a valve opens. Not sure if that is a problem or not. I use 1 gal/hour pressure compensating emitters which work well. Historically, pumps in this well fail after about 10 years due, I think, to 3ppm iron in the water. The pump is starting to go bad and I want to replace it before the growing season, my thinking was I could upgrade the system in the process. I got a bid from a local pump installer for a more robust pump and he recommended a 3-phase motor. Here is the upgrade proposal:

--35-GPM at 50-PSI with a 30ft elevation lift above the top of the well and a 140Ft pumping level down the well
--Gould 35GS30 3 HP 3-phase
--3HP VFD control panel with transducer

I'm not about to go with this proposal as I have doubts about three-phase and this was a very expensive bid.

Because of the complexity of the irrigation system (11/2" supply pipe with a bit of 1" and many hundreds of feet of 5/8" irrigation tubing), I don't have a good idea of pressure loss to friction. Not sure how to figure that out.

My thinking at the moment is to go with the Grundfos SP series with something close to what I have. If it ain't broke don't fix it. But any thoughts about an upgrade would be greatly appreciated.

In a related problem, I use a Mazzie venturi to fertigate the vines. It works perfectly for the two acres that are at well level but will not operate for the hillside grapes. When pumping that 10 to 50 feet higher there is no pressure differential at the venturi. I'm looking into installing a small booster pump before the injection point.

 

[Valveman]

Thanks for the response. I was concerned about the 10,000 rpm on the SQ. I'm going to need more help in figuring all this out. Here is my situation:

The well is used exclusively to water a 4-acre vineyard divided into 5 blocks of 500 vines each. I need ~12 gal/min to provide water to each vine some of which are 10-50 feet above the level of the well. The 2 hp pump sits at 85 feet in a 200 foot 8" inch well that was drilled in 1975. I have the well log and it tested at 50 gal/min at 100 feet. It is a simple system controlled by a standard pressure gauge set at 55 to 75 psi and uses a 350 well-x-trol pressure tank. I believe the pump is undersized because most of the time it runs constantly when a valve opens. Not sure if that is a problem or not. I use 1 gal/hour pressure compensating emitters which work well. Historically, pumps in this well fail after about 10 years due, I think, to 3ppm iron in the water. The pump is starting to go bad and I want to replace it before the growing season, my thinking was I could upgrade the system in the process. I got a bid from a local pump installer for a more robust pump and he recommended a 3-phase motor. Here is the upgrade proposal:

--35-GPM at 50-PSI with a 30ft elevation lift above the top of the well and a 140Ft pumping level down the well
--Gould 35GS30 3 HP 3-phase
--3HP VFD control panel with transducer

I'm not about to go with this proposal as I have doubts about three-phase and this was a very expensive bid.

Because of the complexity of the irrigation system (11/2" supply pipe with a bit of 1" and many hundreds of feet of 5/8" irrigation tubing), I don't have a good idea of pressure loss to friction. Not sure how to figure that out.

My thinking at the moment is to go with the Grundfos SP series with something close to what I have. If it ain't broke don't fix it. But any thoughts about an upgrade would be greatly appreciated.

In a related problem, I use a Mazzie venturi to fertigate the vines. It works perfectly for the two acres that are at well level but will not operate for the hillside grapes. When pumping that 10 to 50 feet higher there is no pressure differential at the venturi. I'm looking into installing a small booster pump before the injection point.

A 2HP submersible set at 85' and delivering 50 PSI should pump up to 28 GPM. It is a good thing that your pump does not shut off when irrigating, as cycling on and off is what destroys pumps. Cycling for smaller zones maybe why your pump is only lasting 10 years instead of longer. Iron in the water doesn't usually hurt a pump unless it just plugs up the intake screen.

Yeah the variable speed or VFD control and 3HP pump is not cheap. But that is just the tip of the ice burg. It is common to have to replace the VFD controller and/or pump at least 2-3 times in the same 10 year period. You know how long it last with the big pressure tank. (WX350 holds 30 gallons of water) Why would you want to change to something that cost more and doesn't last as long? The only problem with the 119 gallon size pressure tank is that the pump still cycles when using less than 25 GPM. Adding a Cycle Stop Valve to stop the cycling will make the pump last longer. The CSV also delivers constant pressure with varying flow rates the same way a VFD does, without all the expense, complication, and short life.

Check the pressure when the pump is running constantly on the zones. If you need more pressure for the zones or for the injector, use a larger well pump instead of adding a booster. Installing and controlling a 3HP well pump will be much easier and less expensive than adding a 1HP booster to a 2HP well pump. A CSV works better than a VFD and can make a 3HP well pump act like a 1/2HP pump when small zones or a shower is being used.

 

[ian morrison]

A 2HP submersible set at 85' and delivering 50 PSI should pump up to 28 GPM. It is a good thing that your pump does not shut off when irrigating, as cycling on and off is what destroys pumps. Cycling for smaller zones maybe why your pump is only lasting 10 years instead of longer. Iron in the water doesn't usually hurt a pump unless it just plugs up the intake screen.

Yeah the variable speed or VFD control and 3HP pump is not cheap. But that is just the tip of the ice burg. It is common to have to replace the VFD controller and/or pump at least 2-3 times in the same 10 year period. You know how long it last with the big pressure tank. (WX350 holds 30 gallons of water) Why would you want to change to something that cost more and doesn't last as long? The only problem with the 119 gallon size pressure tank is that the pump still cycles when using less than 25 GPM. Adding a Cycle Stop Valve to stop the cycling will make the pump last longer. The CSV also delivers constant pressure with varying flow rates the same way a VFD does, without all the expense, complication, and short life.

Check the pressure when the pump is running constantly on the zones. If you need more pressure for the zones or for the injector, use a larger well pump instead of adding a booster. Installing and controlling a 3HP well pump will be much easier and less expensive than adding a 1HP booster to a 2HP well pump. A CSV works better than a VFD and can make a 3HP well pump act like a 1/2HP pump when small zones or a shower is being used.

Thank you for the very helpful information. I'm sticking with my original plan which was to use a single phase 2 hp pump and will use a CSV. I opened up the wellhead today and found significant iron build-up which I'm sure is causing some if not all the reduced performance of the pump.