Reduction pipe for pump?

Discussion in 'Pumps and Tanks Well Forum & Blog' started by sprinkler, Jun 3, 2006.

  1. sprinkler

    sprinkler New Member

    Messages:
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    I am about to install a new Franklin 4" pump (mod SM-3-22) in a 60 meter well.
    The water outlet on the pump is 4 cm diameter but the existing buried pipe from well to house is 2 cm diameter. Would it be ok to fit a reduction adaptor on the pump for the smaller 2 cm pipe?
    The pump specifications: L/H 2400 - 600; max lift - 105 meters; RPM - 2850; CV - 1,00 (736 watts).
    The overall height from well bottom to attic water tank is about 70 meters. And the total length of pipe (including horizontal run) is about 110 meters.
    Thank you.
    Last edited: Jun 3, 2006
  2. Bob NH

    Bob NH In the Trades

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    Location:
    New Hampshire
    I am about to install a new Franklin 4" pump (mod SM-3-22) in a 60 meter (200 ft) well.
    The water outlet on the pump is 4 cm (1.5") diameter but the existing buried pipe from well to house is 2 cm (3/4") diameter. Would it be ok to fit a reduction adaptor on the pump for the smaller 2 cm pipe?
    The pump specifications: L/H 2400 - 600 (10 GPM to 2.5 GPM); max lift - 105 meters (340 ft); RPM - 2850; CV - 1,00 (736 watts) (1 HP).
    The overall height from well bottom to attic water tank is about 70 meters (230 ft).


    I assume that the designation of 2400 - 600 L/H represents the range of performance of the pump. That would be somewhere in the range of a 7 GPM rated pump in the US, such as a Goulds 7GS07. The pumps in the US often have a substantial service factor on the motor so the 7GS07 might be pretty close to your pump.

    You don't say if the tank is a pressure tank or a non-pressurized "gravity" tank. The mention of the attic suggests the latter. If a gravity tank, it would be best if the pump is controlled with a float switch rather than some kind of pressure swith/tank/float valve arrangement.

    At 2400 L/Hr you will have about 25 meters of head loss per 100 meters of 2 cm pipe. At 600 L/Hr the loss will be less than 3 meters per 100 meters of pipe. Your total head loss will depend on the distance to the house.

    If you must stay with the 2 cm pipe, you might consider getting a 1200 L/H pump if it will meet your needs and you have enough storage in the tank.

    In any case, I would use 4 cm pipe in the well where it is not buried. If 4 cm is not available or too expensive, then anything larger than 2 cm would be better.

    You should be aware that the restriction of the small pipe could result in a head/pressure of 105 meters (150 psi) at the point where the well pipe exits the water level in the well. Your pipe should be selected to withstand that pressure.

    The system will probably work if you are careful to use pipe that will withstand the pressure. If I were selecting a pump for the system limited to the 2 cm pipe and a "gravity" tank, I would be selecting a smaller pump with less head, probably a nominal 1200 L/Hr rated pump with a 375 watt or 500 watt motor.
  3. sprinkler

    sprinkler New Member

    Messages:
    72
    Actually I already have the pump. Yes, I just want to fill a simple water tank in the attic which has a floating switch to control the pump.
    Would it be of any help to use 3 or 4 cm pipe just from the well bottom to well top? I would also fit a 4 cm 90º elbow joint at well top. (that would be about 52 meters of pipe) Then connect to the buried 2 cm pipe. Or would it be better to replace the buried section (though a lot of work...) with 3 cm pipe (and connect to the existing 2 cm iron pipe from garage to attic tank?
    Last edited: Jun 3, 2006
  4. Bob NH

    Bob NH In the Trades

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    3,317
    Location:
    New Hampshire
    I would use 3 cm pipe from the pump to the top of the well. That is large enough for 2400 L/H flow.

    I would put a tee at the point where you change to the 2 cm pipe so you can install a pressure gauge. As I pointed out in the earlier post, the pressure down in the well could approach the capability limit of the pipe. Polyethylene pipe is usually available in 100 psi and 160 psi grades. The pressure could exceed 100 psi down in the well.
  5. sprinkler

    sprinkler New Member

    Messages:
    72
    But what would be the exact reason for fitting the tee with pressure gauge to connect from 3 cm to 2 cm pipe. What would the pressure gauge do?
    Would it be preferable to use 4 cm pipe from well bottom to top? (actually the pump documentation says you should use the same size pipe, or bigger, than the water outlet on the pump, which is 4 cm in this case.
  6. Bob NH

    Bob NH In the Trades

    Messages:
    3,317
    Location:
    New Hampshire
    The point of a pressure gauge is to tell you if you are creating too much pressure with the small 2 cm pipe. I like to know what is happening in my systems. If the pressure is high you will know what the risk is with your well pipe. It is not critical to operation and it will not give you any information until you have already made your decisions regarding pipe size.

    A 3 cm "downpipe" will give you about 3 meters of head loss in that pipe; while the 4 cm pipe will result in about 1 meter of head loss in the down pipe. I'm making the estimates based on conversions from my pipe tables which are for inch size pipe. The difference is not that significant. You can make your decision based on cost and availability.

    If cost is an issue, I would rather have 160 psi 3 cm pipe than 4 cm 100 psi pipe.
  7. sprinkler

    sprinkler New Member

    Messages:
    72
    So bottom line is that the only "damage" that might result from using the 52 meters of 3 cm downpipe plus the existing 58 meters of 2 cm pipe, would be that the 2 cm pipe could burst or some connections or elbow joints along the 2 cm pipe might break apart or leak? Or maybe some hammering noise in the pipes? So better to replace any accessible 2 cm elbow joints or pipe runs with the 3 cm diameter?
    But can I assume that the pump itself would not suffer any damage? And I also thought of replacing the 3 meters of accessible 2 cm pipe in the attic, with 3 cm pipe, to reduce the water pressure going into the tank (to minimise "disturbing" the water at the bottom of the tank while filling). What do you think? Thanks a mill.
    Last edited: Jun 4, 2006
  8. Bob NH

    Bob NH In the Trades

    Messages:
    3,317
    Location:
    New Hampshire
    You won't damage the pump as long as there are no shutoff valves anywhere in the pipe, and if the pipe doesn't fail due to excessive pressure.

    Restriction of flow for any reason will cause the pump to produce lower flow and higher pressure at the pump.

    Failure of the pipe in the well could cause the pump to deliver flow in excess of the rating of the pump and could cause the motor to overheat.

    A bigger pipe in the well will produce lower pressure at the pump and higher flow to the tank. 3 cm pipe will work, but 4 cm pipe will produce less pressure at the pump and more flow to the tank.

    I don't have the "pump curve" so I don't have any way of knowing the specific pressure/flow characteristics of your pump or system.

    If you care to know how the system is working, put a pressure gauge at the top of the well. That will not help you with pipe selection because you will have already installed the pipe and pump.

    The pressure of 105 meters is 150 psi, which could exceed the pressure capability of the pipe, depending on the pipe that you use.

    The pressure is highest at the pump and that is the most likely point that a pipe could fail. The pipe could burst or the connection to the pump could fail. If the pipe separates from the fitting it will be left hanging from the wire. If the wire breaks, the pump could be lost down the well. BE SURE THAT YOU SELECT A WELL PIPE WITH A RATING THAT EXCEEDS THE PRESSURE THAT WILL EXIST AT THE PUMP.

    If the pipe doesn't fail, the only effect is reduced flow.
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