How pumping works

lazzalazza Solar Expert Posts: 334 ✭✭✭
HI forum

We're looking at solar pumping solutions for irrigation, and it's all a bit new for me.

I have a simple question:

If I have to pump from a well 36M deep to a tank 4M high. I presume this is a total dynamic head of 40M. Now suppose I put in a Lorentz pump PS1800 C-SJ5-12 that will give me say 60M total dynamic head with 1200W DC (supposing a system of 1600Wp). Will this give me 20 Meters Water Column or 2 bar of extra pressure? Can this pressure then be used by opening the tank valve and irrigating during the pumping hours at 2 bar?

thanks
Larry

Comments

  • BB.BB. Super Moderators, Administrators Posts: 31,171 admin
    Re: How pumping works

    Yes, more or less... What you describe, I think, would be called the static head. And you need to take into account a well drawn down to minimum level and a tank at maximum level (or the level of the outlet above the surface of the water).

    There is also the dynamic portion--Additional pumping resistance caused by water flow/friction in the piping (long lengths of pipe, right angle bends, valves, etc.). So, you should use plumbing tables to take into account any water flow friction too.

    Also, there are two major classes of pumps... Centrifugal which will maintain a constant pressure even if the water flow is zero...

    And piston (and other types) of pumps which pump a fixed volume for every rotation of the pump shaft. These pumps, if pushing against a closed valve (for example) will increase the pressure until the motor stalls or something breaks (shaft, pipe, etc.).

    So, when you get near maximum head, a Centrifugal pump will simply stop moving water (and to a degree, use less power from the motor). A constant volume type pump will load the motor even more until something stalls/overheats/breaks.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • tmarchtmarch Solar Expert Posts: 143 ✭✭
    Re: How pumping works

    A little more information would be helpful:
    1. Why the tank, if you only want to irrigate when the pump is running? You might be better served to put a valve to fill the tank. Then shut the tank off the discharge and irrigate directly out of the discharge which will give you additional pressure. This is what I do with the same pump altho I have additional pressure because my irrigation is below my discharge. I put a float on the tank with a bypass valve below it to direct the water to my irrigation.

    Lorentz has a program to size your pump for depth (head), watts of power etc. My particular set up will pump 6 gallon a minute with 1440 watts or 9.8 gpm with 2220 watts @ 400 feet of head. I'm using the helical rotor pump because of it's added reliability with foreign matter (sand) in the well.

    Basically here the pump ends for Lorentz are all priced the same so any additional cost is in the modules to run it.
    lazza wrote: »
    HI forum

    We're looking at solar pumping solutions for irrigation, and it's all a bit new for me.

    I have a simple question:

    If I have to pump from a well 36M deep to a tank 4M high. I presume this is a total dynamic head of 40M. Now suppose I put in a Lorentz pump PS1800 C-SJ5-12 that will give me say 60M total dynamic head with 1200W DC (supposing a system of 1600Wp). Will this give me 20 Meters Water Column or 2 bar of extra pressure? Can this pressure then be used by opening the tank valve and irrigating during the pumping hours at 2 bar?

    thanks
    Larry
  • lazzalazza Solar Expert Posts: 334 ✭✭✭
    Re: How pumping works

    HI Tmarch

    Basically the tank storage of 60,000 litres is already there. Currently this guy is using a AC pump powered by a generator to fill the tanks.. and wished for a solar pumping system to do the same. However any extra pressure could be used to pump directly as one of the sectors is uphill and lacks a bit of pressure.

    As you say, we could install a valve before the tank and irrigate directly to get added pressure- although that may involve extra costs.

    The lorentz pumps, do they come with a tank float to switch off the pumping system once the tank is full?
  • Texas WellmanTexas Wellman Solar Expert Posts: 153 ✭✭
    Re: How pumping works

    Yes, you can add a float switch to shut off the pump. It's a reverse float switch, I believe the term is "pump up".
  • tmarchtmarch Solar Expert Posts: 143 ✭✭
    Re: How pumping works

    Yes, the float switch is for a electric float, different than what I have which is just a pressure type float that shuts the tank off and a bypass that allows the pump continue to run and move the water for irrigation. The bypass is above the tank inlet so the tank fills first. This kind of system is less expensive than the electric float which is troublesome to set up and takes additional wire etc.
    lazza wrote: »
    HI Tmarch

    Basically the tank storage of 60,000 litres is already there. Currently this guy is using a AC pump powered by a generator to fill the tanks.. and wished for a solar pumping system to do the same. However any extra pressure could be used to pump directly as one of the sectors is uphill and lacks a bit of pressure.

    As you say, we could install a valve before the tank and irrigate directly to get added pressure- although that may involve extra costs.

    The lorentz pumps, do they come with a tank float to switch off the pumping system once the tank is full?
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