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am1958

Unregistered

1

Wednesday, May 22nd 2019, 12:24pm

Replacing dead pump

I have a sprinkler system that draws water from a lake about 3' below the pump and at the highest point in my yard the sprinklers are about 10' above the pump. The existing pump is probably original to the house which was built in 1984. The existing pump is is a 1HP pump with an A.O. Smith pump motor, (I can't find any other manufacturers mark), with a 2" intake and a 1 1/2" output. After trying to prime it yesterday the pump runs and forces water out of the priming tap but is generating almost no pressure at the heads thus I believe the impeller is probably gone. From digging around it seems that replacing the pump will be more cost effective than an attempted repair since the pump is 30+years old.

I'm looking at a 1HP pump that has both a 1 1/2" intake and output. The question I have is will restricting the intake size reduce the effectiveness of the pump or is dropping that 1/2" on intake going to make no difference? My guess is that it does and I should look for a pump with 2" intake and 1 1/2" output but any guidance would be appreciated.

Wet_Boots

Supreme Member

Posts: 5,352

Location: Metro NYC

2

Thursday, May 23rd 2019, 9:23am

You might do better with a different sort of pump. This is because a standard centrifugal pump outputs less pressure than most sprinklers need for best operation. Can you identify the existing pump? (make and model number)

AM1958

Unregistered

3

Friday, May 24th 2019, 6:55am

I can't find anything on the pump other than the motor is an A. O. Smith and it is a 1 HP pump.
Will throttling back the 2" intake to 1 1/2" disaffect the performance or would I be ok?

Wet_Boots

Supreme Member

Posts: 5,352

Location: Metro NYC

4

Saturday, May 25th 2019, 7:47am

Right now you are deep within the guessing zone. So much is not yet defined. How many heads per zone? What is the flow per zone? For most lake-fed systems, your best pump is something different that what you had, or the replacement pump you're considering.

Consider a jet pump. The design of a jet pump recirculates some of the output flow back to the intake side, in order to give an output pressure that is higher than a straight centrifugal pump can supply. Sprinkler systems need pressure more than they need flow.

Note that your intake-size question is totally not relevant for a 1 HP pump. A 1 HP centrifugal pump can move about 40 gpm maximum (that 40 gpm will not be at a pressure you can run sprinklers with) and that flow is not enough to make the difference between a 2 inch inlet and a 1-1/2 inch inlet in any way meaningful. It is obvious that your existing pump is of a series of models that includes higher horsepower versions.

Once you know how much flow and pressure you actually require from your pump, you can make a proper selection.

Here's a chart for Goulds JS series jet pumps. The flow of jet pumps is such that the inlets only need to be 1-1/4 inch, even for the 1.5 HP model.


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