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Question about pumps for rainwater tank  RSS feed

 
Grant Cee
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Hi everyone! Been a lurker here for a while, and have found answers to many rainwater harvesting questions. This one, though, has me a bit confused.

I have a 1250 gallon tank which is now full of water (connected it to the gutters last fall.) It sits next to our large garden, with the far end of the garden being about 125 feet (38 meters) from the tank and with a slight uphill slope (about 3 feet/1 meter total rise over that distance.)

I want to use the water in the tank solely for watering the garden, which my wife prefers to do with a handheld hose. I think some sort of demand pump is in order, but am unsure whether they're capable of pushing a column of water that far.

We have 110v power available at the tank, so no need for a 12v system.

Do you have any suggestions? Is a demand pump appropriate, or should I go with a conventional pump and pressure tank?

Thanks!

- Grant
 
wayne fajkus
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Harbor freight hs a combo well pump w built in pressure tank for well under $200. They have lasted a year.  I finally gave up on them.

Groundfos pump, which is $600+ turns on/off as needed. Will shut itself off if the tank is dry. They've lasted me 5+ years. It doesn't need a pressure tank. It can provide pressure for a house.

Both are 110v.
 
Druce Batstone
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Welcome Grant. For hand held hosing you do not need a pressure tank. A simple electric water pump will do the job. Look on Ebay. I saw one in the US for $35.

I have something similar connected to my tanks. Single impeller centrifugal pumps will operate without damage if the outlet is closed and for a short time if the tank runs empty. They produce more than enough pressure and flow for hand watering. Mine supplies a trickle irrigation system.

 
Grant Cee
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Druce Batstone wrote:Welcome Grant. For hand held hosing you do not need a pressure tank. A simple electric water pump will do the job. Look on Ebay. I saw one in the US for $35.

I have something similar connected to my tanks. Single impeller centrifugal pumps will operate without damage if the outlet is closed and for a short time if the tank runs empty. They produce more than enough pressure and flow for hand watering. Mine supplies a trickle irrigation system.


Thanks! Can you give me an idea as to the size (in hp) of the one you have?
 
Druce Batstone
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The electric motor on the pump is 1/2 hp (0.37 kW). By way of further explanation, we have two other rain water tanks each with a separate pump for hand hosing on our suburban block. My wife is like yours in that regard. These have been in use for more than 10 years with no problems. They also have 1/2 hp and are fitted with an electronic controller that stops the pump if the hose is turned off. The controller is not really necessary for hand watering or trickle irrigation.
 
Bobby Keeland
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Location: Southern Louisiana
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We have a Grundfos pump to supply our house, up to a second floor. It is on demand and works great. It is rather expensive but has only been in use for 6 months.

I'm also thinking about finding a less expensive pump for a separate tank to be used for greywater for irrigation purposes only.
BobK53
 
Tony Paul Martin
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If you use a larger diameter pipe it will improve flow and reduce the amount energy needed to pump.
You might find this article on sizing of hosepipes of interest.
http://www.what-is-permaculture.co.uk/articles-by-tony
 
John Schinnerer
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For a demand pump for this application, simplest would be a 110v diaphragm pump - shurflo, flojet, many other brands. Starting at around $80 or so. Expect to pay $100-$150 for a decent to really good one.
These are used for demand pressure on boats for example. Also for low-end pressure tank systems from catchment sources (often with a tiny tank, which is poor design, because the pump cycles on and off frequently - a main purpose of a pressure tank is to reduce pump cycling).

Be sure to put an on-off switch for the pump where the hose is stored. Turn it OFF whenever you're not actively watering so that a leak in the hose or nozzle or fittings or whatever doesn't drain your tank dry when you're away from the system.

3-4.5 GPM max, and usually 35-40 psi max, if you need more flow volume than that or more pressure than that (not likely for this application) you'll need a more expensive one or a different type of pump.

A few additional considerations...

Pros
Simple, cheap, reliable.
Can run dry with no harm.
Diaphragm pump part can be rebuilt, rebuild kits ~$40-$50.
Can handle some particulates & murkiness in the water (needs a mesh screen filter on inflow but nothing fancier).

Cons
Noisy as heck, in a bad annoying I-hate-that-sound way. If you've never heard one, find a way to hear one before you commit or you may regret it. Or plan to put it in a sound-insulated box.
 
Steve Crane
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Location: Lagos Portugal
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Hi Grant.

Why not raise the tank by a small amount?
 
Dean Howard
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Location: NE ARIZONA, Zone 5B, 7K feet, 24" rain
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Steve Crane wrote:  Why not raise the tank by a small amount?


One simple fact to consider if you can't raise the tank, as wisely suggested by Steve, is head-pressure.  If you have plenty of rain and keep your tank at least half full, I would be surprised if you couldn't easily have enough water pressure to garden slightly uphill.  It depends on the capacity and shape of your tank, and distance, but it may work just fine for you.  When rain fails to completely fill your tank, you still have half a tank of water to use.  I was looking at a small 12V pump just last night on Amazon for $11.  There are tons of them for sale.
 
Mario Lazetti
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Location: 6b Atlantic City NJ
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Wouldnt it be possible to set up a self priming ram pump to the tank? Wouldnt need to bother with more expensive option or even need electricity.
 
Grant Cee
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Steve Crane wrote:Hi Grant.

Why not raise the tank by a small amount?


Because raising a 1250-gallon tank is neither easy nor cheap to do — especially when it's inside a building, as this one is.

The next tanks will be located on a high point on our property!
 
Grant Cee
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An update on my project:

I ended up installing the suggested pump/tank combo from Harbor Freight (largely because I had a coupon!) It's atypical for an HF product: well made, nicely finished, clean machining, and generally good material choices. Installation was easy and it works like a charm.

Thanks for the recommendations!

-=[ Grant ]=-
 
Mike Jay
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Hi Grant, which Harbor Freight pump did you use?
 
Grant Cee
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Mike Jay wrote:Hi Grant, which Harbor Freight pump did you use?


Their #63407, "1 HP Stainless Steel Shallow Well Pump and Tank with Pressure Control Switch - 950 GPH"
 
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