Feed pump for a beach cistern:

SystemSystem Posts: 2,511 admin
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 WaterCube from Danfoss. The flow rate needed 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 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

Comments

  • mike95490mike95490 Solar Expert Posts: 9,036 ✭✭✭✭✭
    Re: Feed pump for a beach cistern:
    szimmer wrote: »
    Hello!

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

    Simon

    What is the LIFT needed, horizontal run is almost a no-load.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • System2System2 Posts: 6,290 admin
    Re: Feed pump for a beach cistern:

    The lift would be about 40 feet. I need to calculate the fact that there are two pre-filters in the Watercube right?

    So the depth of the cistern is 10 feet. 1 pre-filter equals 15 feet added to the lift so adding both pre-filters adds another 30 feet which equals about 40 total for the lift.

    Am I missing something?

    Simon
  • mike95490mike95490 Solar Expert Posts: 9,036 ✭✭✭✭✭
    Re: Feed pump for a beach cistern:
    szimmer wrote: »
    The lift would be about 40 feet. I need to calculate the fact that there are two pre-filters in the Watercube right?

    So the depth of the cistern is 10 feet. 1 pre-filter equals 15 feet added to the lift so adding both pre-filters adds another 30 feet which equals about 40 total for the lift.

    Am I missing something?

    Simon

    How many GPM do you need 0.5, 30 ???
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • BB.BB. Super Moderators, Administrators Posts: 31,077 admin
    Re: Feed pump for a beach cistern:

    Hmmm, a submersible pump in saltwater--I don't know how much good can come from that...

    Can you build a sump with buried piping to a pump pit a few hundred feet away/on the shore (or perhaps an inland sump/well, and you perhaps get brackish water since it floats on saltwater) and use a damp location pump with a suction hose--try to keep everything out of the salt water you can and make the parts cheaply replaceable).

    Perhaps looking at marine and off-shore oil equipment catalogs and talking with a couple sales engineers can give you an idea what would last in that environment.

    Even the WaterCube folks should be able to give exact recommendations.

    If possible, it would be nice to pump the feed water up to an elevated tank and just cycle the pump when the water drops--generally it is more efficient than trying to throttle the volume. Alternatively, use a surge tank (are over water w/ bladder) to give you the ability to cycle the pump (like a home well system)--again, salt water is not going to be friendly.

    Lastly, you probably will need sacrificial zinc anodes to help reduce corrosion/electrolysis.

    Have the Danfoss people given you any suggestions?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2System2 Posts: 6,290 admin
    Re: Feed pump for a beach cistern:

    Hey Bill.

    Yes, Danfoss recommended Grundfoss but did not go into specifics as far as which specific pump or setup.

    As for GPM, I mentioned 2 gal/min to 5 gal/min in the first post.

    Any other info needed?

    I will look into the ideas you mentioned Bill but no matter what the solution is, it will have to be durable against salt. Even brackish water will have a high enough salt content that it would eat through anything not protected.

    Time for dinner.

    Later!

    Simon
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Feed pump for a beach cistern:

    simon does pose some challenges doesn't he?
  • WindsunWindsun Solar Expert Posts: 1,164 ✭✭
    Re: Feed pump for a beach cistern:

    It looks like the 11SQF-2 with around 170 watts of panel would do it. Well, more panel, since you are running off of battery at night, so probably 300 watts or so into a 24 volt battery system.

    I have not had time to really analyze it, but that should give you a start point.
  • System2System2 Posts: 6,290 admin
    Re: Feed pump for a beach cistern:

    So using this submersible pump in salt water is not an issue?

    Is there an advantage or disadvantage of using a helical pump compared to centrifugal?

    Simon
  • System2System2 Posts: 6,290 admin
    Re: Feed pump for a beach cistern:

    Niel you are right!

    But life would be boring if there were no challenges!

    Simon
  • System2System2 Posts: 6,290 admin
    Re: Feed pump for a beach cistern:

    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
  • System2System2 Posts: 6,290 admin
    Re: Feed pump for a beach cistern:

    I got some more information from Danfoss regarding the feed pump requirements for the Watercube.

    Minimum pressure: 2 bar (29 PSI)
    Maximum pressure: 5 bar (72.5 PSI)

    Their recommendation is to get it as close to 5 bar as possible and this will prolong the life time of the pre filters, as they have a larger span of pressure drop to work on.

    The ideal flow rate is still at 5gpm.

    Having received some good feedback from various sources, we like the idea of possibly putting the pump on top of the cistern therefore eliminating the issue with having a pump always submersed in the salt water. So we would put a concrete lid on top of the cistern with a hole in it for the PVC pipe going down into the cistern. The pump would be on top with some kind of housing to protect it from rain, debris, etc….

    We found some interesting plastic pumps which have no problems dealing with the salt water. The only issue may be the ambient temperature may not be high enough if the pump is outside instead of inside.

    Simon
    p.s.
    Danfoss confirmed that there is an issue with having a feed pump (positive displacment) feeding a high pressure pump that is also positive displacement. It creates pulsation which is bad for the high pressure pump.

    There fore the helical pumps from Grundfos would not work!
  • System2System2 Posts: 6,290 admin
    Re: Feed pump for a beach cistern:

    For those of you that are curious, we have decided to go with the submersible pump from Lorentz:

    http://www.lorentzpumps.com/offgrid/en/products/ps/150/_performance

    It is not the perfect solution but the best solution we have found so far. We will however, test it out in our testing facility first to see how it performs with the Watercube.

    We like this one because it is made out of 316 SS and we have a bias for well-built equipment made from Germany. We also found a contact in Colombia that uses and sells them and he said they are excellent for what we want to do.

    Thanks for everyone's two cents on the matter.

    Simon
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Feed pump for a beach cistern:

    no problem on the 2 cents, but it is unusual in that you gave yourself 5 cents. anyway, no problem in doing so as we can all learn something through it so keep us informed as to how it works out for you.
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