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Old 05-07-2012, 11:12 PM   #1
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Need advice on irrigation pump

Not sure if this question should have been posted in the electrical, plumbing or landscaping section?

I have a lakefront home. Instead of using city water (and paying the high fees) for sprinkler and car washing, I want to use a water pump and suck it from the lake.

I tried a 3/4 hp spa pump. The setup was that the suction hose was about 75' long but only about 1' high (sucking up), and then the "push" hose was about 20' long totally horizontal - hoses are 1" diameter I believe. Anyway this was a total failure. First it was a pain in the ars or prime and even when primed it barely was able to push any water pressure at all.

I then tried a surplus sump pump. Not sure of the specifications. It was installed right onto the lake, so no suction hose needed. So from the water, the "push" hose was about 75' feet. Seemed OK pressure, but when attached to a spinkler it barely is able to make any water even shot up a foot or two (not nearly enough pressure).

So before I go out and buy another pump, I'd like some advice on the hp and gph that I need for my setup. I'd prefer a pump that doesn't need to be submerbed since it is a lake a with many people swimming and playing all the time and I guess an electronic device submerged scares me.

BTW - I assume the electrical cost of running an adequate pump will be much cheaper than using city water? Is this normally the case? Not sure what my water costs me (too lazy to get my bill) but from what I recall it is about $5 for a bathtub full of water.




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Old 05-08-2012, 06:46 AM   #2
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The cost of water is all over the place in the United States. I did a military project in Texas, and we examined some options for saving water. Turned out the water was so cheap it wasn't worth installing a cistern to store water. You may have a similar situation, definitely worth checking your bill before embarking on a pumping odyssey.

Should you decide to pump, you need to compute the total head required. This will include pipe losses due to flow, static losses due to the elevation difference between the lake and the land where you are pumping to, and the losses through the sprinkler system, which you should be able to get from the sprinkler manufacturer. Let's say total losses come to 5 psi. Then you need to know the required pressure to run the sprinklers, which could be as much as 40 psi, again the sprinkler manufacturer should have that data. You then need to get a pump which can deliver the required flow at the required pressure.

A single hose usually delivers about 3 gallons per minute, so depending on how many hose equivalents your system will be, that will be the gpm required of the pump. The combination of gpm plus total head will determine how much HP the pump needs to be, and will also determine the type of pump. Some pumps are good at putting out a lot of pressure at low flow (a well pump for example), while others are designed to put out a lot of flow at relatively low pressure (a sewage pump for example). Some pumps put out a lot of flow at high pressure (a fire hose pump). Until you know what you need, you are guessing at what type of pump to use.


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user1007 (05-08-2012)
Old 05-08-2012, 02:03 PM   #3
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One option to think about designing for everything but watering your lawn. Drip systems require very little operating pressure and flow rates in gallons per hour, not gallons per minute. And with emitters, you just put water where you want it. Emitters come in all configurations you can imagine with outputs from about .5 on up to 12 gallons per hour. Drip systems can water anything but turf.

Turf sprinklers, as mentioned, require a fair amount of pressure each and unless you want to run a pipe to each one even more when factored together. And of course the work in gallons per minute of required flow

So as suggested, what you really do want to do is design backwards. You will need to know the length and diameter of your pipe runs---especially for the lawn sprinklers---and their combined pressure and flow rate. You can then figure flow and pressure loss through valves, pipe and fittings.

I hate that most water utilities in the US are owned by foreign companies but it is still a pretty good deal. In my state we are running out of fresh water though. So I admire you for exploring this option, if you are not going to draw more water out of your lake than gets put back into it! And doing so does not effect some other sensitive ecosystem having to do with water flowing in and out of your lake.

By the way, I should think you can find, and probably will need, an external pump and do not need a submersed one. If using lake water you will want to be sure and build decent filtration into your system or you will be cleaning sprinkler heads and replacing drip emitters for eternity.

Don't underestimate permits you might need for this, by the way. When I worked for a specialty of the Illinois Department of Natural Resources I saw so many people get in trouble doing fineable things assuming because it was their land they could automatically do whatever they wanted it with. Sometimes people did such environmental damage to all other land around it theirs was seized or lost because they could not pay the fines for the damage they had done. I don't remember anybody at DNR or IL-EPA not willing to bend over backwards to help people with projects. Some of the land Illinois is now stuck with, without tax revenue, may come back to some form of life in decades. Some neighboring property owners remain annoyed somebody did not do something sooner. They were the same ones that did not want government involvement in anything. Very amusing.

Last edited by user1007; 05-08-2012 at 02:09 PM.
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