Need advice on a new installation

Discussion in 'Pumps and Tanks Well Forum & Blog' started by sgrd0q, Oct 9, 2008.

  1. sgrd0q

    sgrd0q New Member

    Messages:
    8
    Here’s my situation – new house and well. The well is 300ft deep and the water is at 60 ft below the ground level, so I have about 360 gallons of storage in the well. The yield is only 1gpm. Two and half baths, washer, washing machine, etc. Also I am off the grid, running on a generator and batteries. My electrician suggested I should get a pump that is soft-start and no more powerful than 3/4 HP.

    Based on this and after talking to my plumber I got the Grundfos 5SQ07-320 pump, and a wx-250 tank. The pump will be installed at 280 ft, i.e. 20 ft above the bottom of the well.

    Assuming 30-50 pump cut-in/cut-out, and looking at the Grundfos performance chart at 30 psi, the flow will be between 8 gpm and 4.4 gpm depending on the water level in the well. How realistic are those numbers? Do I have to adjust for friction loss, etc. considering the pump will be almost 300 ft down?

    Also, let’s say the demand exceeds the pump output for a long period of time. What happens to the flow after the pressure drops below 30 psi ? Does the flow get interrupted because the air is completely expanded in the tank at, say, 28 psi or is there a bypass valve of some sort to allow the water to bypass the tank? In the latter case I would imagine the pressure will continue to drop until the pump can keep up with the demand (maybe, say at 20 psi).

    The wx-250 tank has a draw down of about 15 gallons at 30-50 cut-in/cut-out. Is there a way to make sure that first thing in the morning before anyone has taken a shower the pressure is at 50 psi? I would like to avoid the situation where the pressure was left at, say, 31 psi from the night before, and there is little to no reserve of water in the tank.

    Finally, what do you think of the Cycle Stop Valve? On the one hand I like the constant pressure, on the other I understand you lose 1/2 gpm of the flow, which is significant in my situation. I am not too concerned about the number of cycles, as the tank is sized appropriately relative to the output of the pump. Also, I am not too concerned about the startup spikes in electricity, as the pump is soft-start. I would like to have a more constant pressure in the system, though.

    Thanks for your help and advice!
    Last edited: Oct 9, 2008
  2. speedbump

    speedbump Previous member

    Messages:
    4,540
    Location:
    Riverview, Fl.
    At 280 feet that pump is still producing around 7 gpm. This is a good flo for home use. Remember that the pump is starting at 60 feet. It's pumping a lot better than 7 gpm there. You didn't say what size the casing was, so I'm not sure about your storage. The CSV will work great in your situation and you will have great pressure until the water level gets down to the pump. Then you will have none. Learn to use water conservativly.

    Did you drill a 3" well? If not, why in the world did you use a 3" pump?

    bob...
  3. sgrd0q

    sgrd0q New Member

    Messages:
    8
    Thanks for the reply. The well is 6", so it stores a gallon and a half per foot. I figured I'd have more than 300 gallons of water storage in the well, so that should be ok.

    I had to get a soft-start pump (off grid application), so that's why we picked that specific pump with my plumber. I am not sure if that is the best choice. What would you have recommended?

    The flow when the water level is at 280 will only be 4.4 gpm if the pressure in the tank is 30 psi. That's my interpretation of the charts, but I may be wrong.
    Last edited: Oct 9, 2008
  4. speedbump

    speedbump Previous member

    Messages:
    4,540
    Location:
    Riverview, Fl.
    I am very familiar with the Grundfos three inch pumps since I sell them. They are soft start and turn 10,500 RPM's once up to speed. I would think the 4" pumps come with the same electronic motors, but I may be wrong. I do know the 4" would have been cheaper than the 3".

    Your reading of the pump curve is right on, but since in about two seconds from that point your going to be totally out of water, it won't make much difference.

    I don't think a Pumptec or a Cycle Sensor will work on the Grundfos motor. Maybe Valveman or someone else knows the answer to that one. I wouldn't want to depend on the Grundfos electronics to be the only thing protecting itself.

    bob...
  5. nhmaster

    nhmaster Master Plumber

    Messages:
    3,189
    Location:
    S. Maine
    The only thing I would add is a pressure switch with a low pressure cut out in case you overpump the well.
  6. valveman

    valveman Moderator Staff Member

    Messages:
    4,495
    Location:
    Lubbock, Texas
    The Cycle Sensor will work with the SQ, because it looks at low amperage for 5 seconds before tripping out on dry run. This gives time for the soft start to get up to speed and pull the right amps. A low pressure cut off switch will usually work also. However, I have seen several occasions where the faucets were shut off at about the same time as the well ran dry. Then the pump has lost prime but, the pressure doesn't fall off and let the low pressure switch shut the pump off. A Cycle Sensor doesn't care about the pressure. It will shut the pump off on low amperage from a dry well, even if the faucets are closed and the pressure doesn't fall off.

    A CSV will also work well with an SQ. The friction loss won't keep you from getting the 4.4 GPM when the water level is low. You will still get 4.4 GPM, it will just be at about 25 PSI instead of 30 PSI. Friction loss either gives you the same flow at lower pressure, or lower flow at the same pressure. The little extra friction loss from the CSV is usually a good thing in these kinds of wells, as it will keep the pump from upthrust when the water level is high. With that size tank, I would set the CSV at about 45 PSI. This will give you 45 PSI constant while you are using water, in stead of the pressure bouncing between 30 and 50 all the time.

    Oh yeah, and I don't think you can get a domestic size 4" motor from Grundfos with a soft start. Other companies make them but, they have other problems as well.
  7. sgrd0q

    sgrd0q New Member

    Messages:
    8
    Thanks for all the information. I may order the CSV tomorrow.

    I am still curious - if the pump cannot keep up with the demand what happens when the pressure drops below 30 psi? This is assuming the pump cut in/out pressures are set at 30/50, and the pressure tank is set at 28 psi. Once the pressure goes down to 28 psi is there a total loss of water pressure, or does the pressure go down gradually to 25 psi, 20 psi, etc?
  8. drick

    drick In the Trades

    Messages:
    392
    Dropping below 28 psi does not cause instant water loss. It just means your pressure tank has no more water in it. Your pressure will just continue to slowly drop until you run the well dry, and then you will instantly go to 0.
  9. sgrd0q

    sgrd0q New Member

    Messages:
    8
    Thanks again for all the replies. I just ordered the CSV1Z.

    I am going to have the pre-charge tank pressure at 28 psi, the pump cut in/cut out at 30/50 psi and the pressure for CSV1Z at 40 psi. (Tank has 15 gal draw down, pump will pump between 4.4 and 8 gpm depending on well water level).

    So this is my understanding of how the valve works:

    Initially the pressure is at 50 psi. Once there is water demand, say at 3 gpm, the pressure will drop all the way to 30 psi. Then the pump kicks in and the pressure builds up to 40 psi, at which point the valve stabilizes the pressure. Once the demand drops to below 1 gpm (or 0 gpm) then the pressure will slowly go up to 50 psi and the pump turns off.

    Is that correct? If it is, then there is an initial big swing in pressure until the pressure stabilizes, or am I wrong?

    By the way my plumber has never heard of this valve - is the installation/setting of the pressure easy?
  10. valveman

    valveman Moderator Staff Member

    Messages:
    4,495
    Location:
    Lubbock, Texas
    The normal pressure drop from 50 down to 30 is what allows you to be able to use all 15 gallons from the tank before the pump starts. You can narrow this to a 40/50 pressure switch setting, with the CSV set at 45 PSI. This will keep you from going all the way down to 30 before the pump starts but, also cuts the water available from your tank to 7.5 gallons. This is still OK, as many people use the CSV with much smaller tanks than that.

    I would still set the CSV at 45 pounds regardless. This is as easy as turning a bolt until the pressure steadies at 45, while running about 2 GPM somewhere.

    Other than that, you are on the right track. The CSV still won't keep you from pumping the well dry, if you use more water than the well can produce. It doesn't matter how much water is in the tank, only how much your well and pump will produce. Your pressure will drop below 30 PSI, anytime you are using more water than the pump can produce from that water level at that pressure.

    Your pressure will be low if you use too much water but, you won't run completely out of water until the water level drops below the intake of the pump. This is when the Cycle Sensor would be helpful. It will shut the pump down on low amperage, let it time out until the well has had time to recuperate, then automatically start the pump again.

    The CSV will eliminate cycling and deliver constant pressure. The Cycle Sensor will protect your pump from dry run. Together, they deliver constant pressure and protect your pump from dry run.
  11. sgrd0q

    sgrd0q New Member

    Messages:
    8
    Very good explanation - thanks!

    One other question - is the SCV valve going to interfere with the draining of all the water when I "winterize" the house for the winter?

    Also, being off-grid I am concerned about the electrical consumption - is the valve going to increase the electrical consumption ?

    I already ordered the valve, but then I thought of these issues...
  12. valveman

    valveman Moderator Staff Member

    Messages:
    4,495
    Location:
    Lubbock, Texas
    It would take a lot of batteries to run a 3/4 HP pump for very long, so I assume you are running the pump with the generator? In that case the CSV will make the pump run continuously while you are using water, instead of cycling on and off. For instance while taking a shower, the CSV will make the motor draw about 4 amps steady, instead of only being on half the time drawing 7 amps, and being off half the time drawing 0 amps. It uses a little more energy per gallon with the CSV but, doesn't continually load and unload the generator as when the pump cycles on and off.

    For winterizing, you need to drain off from both sides of the CSV. Draining the lines to the pump will drain the inlet side of the CSV. Draining the lines to the tank will drain the outlet side of the CSV.

    There really is no way to make sure your tank is full before shutting it down. That is unless you just make sure the pressure is up to 50 and the pump shuts off before shutting down the generator. A WX-250 tank only holds about 15 gallons of water anyway. It would let you flush a few toilets in the middle of the night but, the pump will have to start to take a shower. If the pump has to start to take a shower anyway, it doesn't matter if there is 15 gallons or just 1 gallon in the tank when you start. I have seen systems where the pressure switch actually started and stopped the generator as needed.

    If you had a 1000 gallon pressure tank or about 7 of those WX-250 tanks, you would have about 100 gallons of water stored under pressure. This is the only way I know if to be able to use water for a while without the pump having to run. The pump is still running the same amount of time this way. It will just run one long time for every 100 gallons instead of 7 shorter times.

    Another way to live off the grid is to use a 1000 gallon storage tank, (not a pressure tank). Fill this tank with the submersible and you have 1000 gallons stored. Then you could use one of those demand type pumps like in an RV, to pressure up the water for showers and stuff. These demand type pumps are much smaller and will run off batteries for quite a while. Then the generator is only used to fill the 1000 gallon tank.
  13. alternety

    alternety Like an engineer

    Messages:
    671
    Location:
    Washington
    If it is not too late, change out the pump for one from Dankoff. The range of non-centrifugal pumps will provide the best performance for off-grid use. They work from DC.
  14. valveman

    valveman Moderator Staff Member

    Messages:
    4,495
    Location:
    Lubbock, Texas
    Grundfos and several others also make a non-centrifugal pump that will run on DC. Although it is hard to balance and bush a helical shaft in a pump, so I have never seen one that would last very long. However, they will lift water at very low RPM's which works better with batteries. Do not use a CSV on a pump with a helical shaft or any other type of positive displacement pump.
  15. sgrd0q

    sgrd0q New Member

    Messages:
    8
    I already got the pump, so it's too late to get another one. I will be off-grid, but will have a fairly large battery system and a generator. The batteries will have 25 kW of useable power, so the generator will run only once every day (or every other day) to charge the batteries. All power will be AC coming from two inverters for a total of 8kW maximum continuios power.

    If the penalty for the CSV is only 5-10% I will go with it, if the power consumption is alot higher, I may have to go without it.
    Last edited: Oct 15, 2008
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