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Thread: What kind of feed pump is required for a cistern?

  1. #1
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    What kind of feed pump is required for a cistern?

    Hello!

    What type of feed pump is recommended for a shallow beach cistern with the dimensions at about 10 feet and 3 feet wide? The cistern will be located on a beach near a lagoon and ocean.

    The feed pump will be providing water for the water purification system from Danfoss called the Watercube. The flow rate needed for the feed pump is between 2 gal/min and 5 gal/min. The high pressure pump from the Watercube is a positive displacement pump so I heard that a centrifugal feed pump would be the best fit. Can anyone validate that?

    The distance between the beach cistern and the water cube should be about 20 feet.

    The lift of the feed pump should be around 40 feet.

    The feed pump will be using power from batteries (size unknown at this point).

    Looking at the SqFlex from Grundfos, the 25 SQF-3 Centrifigal pump looked like a possibly good fit. However, I was not sure if it would run properly at lower levels since it is meant for up to 16 gal/min. Also how much amperage does the pump draw? Is there any amperage surge at start-up?

    The water will be salt water at about 35100 TDS. Therefore, the pump needs to be able to handle salt water.

    The pump would be running around 15 hours or so per day.

    Any recommendations on a possible feed pump for this project would be appreciated.

    Simon

  2. #2
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    What type of feed pump is recommended for a shallow beach cistern with the dimensions at about 10 feet and 3 feet wide? The cistern will be located on a beach near a lagoon and ocean. I don't think the size of the Cistern is a concern.

    The feed pump will be providing water for the water purification system from Danfoss called the Watercube. I couldn't find the Watercube on the Internet, so I'm not sure what it does. I believe it's a desal unit. The flow rate needed for the feed pump is between 2 gal/min and 5 gal/min. Now, do you mean that the feed pump your looking for has to only put out 2 - 5 gpm? If so, what pressure does this feed pump have to produce? The high pressure pump from the Watercube is a positive displacement pump so I heard that a centrifugal feed pump would be the best fit. Can anyone validate that? Not without more information.

    The distance between the beach cistern and the water cube should be about 20 feet.

    The lift of the feed pump should be around 40 feet. If you mean vertical lift from top of water to feed pump, it won't work. Centrifugal pumps can only lift water 25 feet max.

    The feed pump will be using power from batteries (size unknown at this point). All the pumps I sell are AC. You would need an inverter capable of handling the horse power of the motor required and the starting inrush current.

    Looking at the SqFlex from Grundfos, the 25 SQF-3 Centrifigal pump looked like a possibly good fit. However, I was not sure if it would run properly at lower levels since it is meant for up to 16 gal/min. Also how much amperage does the pump draw? Is there any amperage surge at start-up? Yes there is a surge on capacitor or inductance start motors. I'm not real familiar with Grundfos pumps. If you only need 3 - 5 gpm, your looking at totally the wrong pump.

    The water will be salt water at about 35100 TDS. Therefore, the pump needs to be able to handle salt water. You might want to consider a plastic pump. Even the stainless pumps don't like salt water. You are probably going to end up with a Hypro or a Flojet or a Shurflo type pump. They are used in motor homes, they are DC and pump around the amount of water per minute you are talking about.

    The pump would be running around 15 hours or so per day. That shouldn't be a problem.

    bob...


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  3. #3
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    Yes, the Watercube is a desal unit.

    It is very new which is why you could not find any information on it yet.

    As you can see, I am new to the "feed pump" field. So I should be looking for a plastic pump that takes DC. Let me check out the Shurflo pumps and see what I can find.

    Thanks for the info.

    Simon

  4. #4
    Pump guy speedbump's Avatar
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    Ok Simon,

    I think Shurflo is probably the most popular. I have one for spraying weeds from my golfcart and it works great. It has a built in pressure switch that works great too.

    bob...

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  5. #5
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    Let me know what you find or your exact requirements, I carry many marine and RV pumps for different applications. I'm a marine dealer, repair service and may be able to help.

  6. #6
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    I didn't know that Jeff. Do you carry Shurflo or the other brands?

    bob...

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    I just spoke with Grundfos and they recommended the:

    16 SQF -10 centrifugal submersible pump

    I was not sure they had this model since it was not in the brochure. It is a centrifugal type of pump which is necessary since a helical pump can create issues since it is a positive displacement pump and so is the high pressure pump in the Watercube.

    The pump is made out of stainless steel 1.4301 (304 AISI). The guy said it should be no problem submersed in salt water but our technical director here has his doubts. What do the experts think here?

    Thanks,

    Simon

  8. #8
    Pump guy speedbump's Avatar
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    Again, I'm not too familiar with Grundfos so I don't know what pump they are referring to. I would think any centrifugal can pump at least 30 gallons per minute and you only need 3 - 5, so why waste the energy. Go with one of Jeffs pumps. They are much less money than Grundfos and probably more suited to what you need.

    bob...

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    Hi Jeff,

    I described what I need in the first post.

    What do you recommend compared to Grundfos?

    Thanks,

    Simon
    p.s.
    Sorry for putting this message in the wrong area before!

  10. #10
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    I just went through over 30 pages of DC pumps from about 10 manufacturers and can't find any that will do what you want. Even your Grundfos seems to take a minimum of 30VDC to operate so at least three batteries would be needed, in addition the length of time the pumps would be running will exhaust almost any battery set.
    The other problem I am running into is being able to pump up 40 feet. None of the pumps I can get can come close to that.
    I too have doubts as the the longevity of even a stainless submersible pump in high concentration salt water. While the casing would probably be OK the electrolysis between even the casing and SS screws would be a concern.
    I would be looking for a pump outside the cistern.
    Wish I could help more.


    BTW I'm not an expert, just hang out here because Bob likes me.

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