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Looking for low producing well advice...
I'm curious if anyone here has experience with a low producing well (i.e. under 1 Gal/min in well tests)? Some say if you use a large 500 - 1000 gallon (usually underground) storage tank they work fine with the right hardware and equipment. But I'm curious how you deal with the well "running dry" without damaging the pump, etc?
I ask because I'm considering buying a property with just such a well. The average household needs around 150 - 300 gallons a day of water if they're reasonably frugal. That works out to only about 0.2 gal/min. But, I would think, designing a well system to work under such conditions is very different than the typical 6+ GPM well.
Does anyone have any comments or advice?
A Pumptec from Franklin or a Cycle Sensor from Cycle Stop Valves will protect the pumps from dry-run damage.
http://www.franklin-electric.com/res...n/pumptec.aspx
http://www.cyclestopvalves.com/prod_sensor_geninfo.html
A 1 GPM well will produce 1,440 gallons per day. How much storage there is in the well casing and what depth the pump is set at plus the GPM of the pump will determine how it needs to be setup.
I use a 3000 gallon tank for 600 bucks, and pump a well at 2gpm or less through a standard 80 gallon pressure tank with a low pressure cut off switch, about 20 bucks. The tank has a float and another submersible pump in it to another small set up for a small house.
You could use the pumptek, and pump it all out until it shuts off and then starts again, but I dont like taking the water level in the well so low, and spinning the pump dry for a moment. pulling sediment from the well bore. Or use the well tek and throttle down the flow to perhaps 3GPM to reduce shut offs. Depends on how much water stands in the well casing. Or get a tiny pump and fill the tank at 1gpm. But you will need 2 systems.
If he throttles flow to 1 gpm he has MADE a cycle stop valve on the well side, and the pump will run full time either way.
Last edited by ballvalve; 02-12-2012 at 10:55 AM.
I would find out more about the well before I bought the house. A 1GPM well could easily become a 0GPM well in a drought. This is less likely with a deep well, but I'd ask the current HO if they ever ran out of water and the well did not recover in 24HRS.
That said you can easily live with 1GPM, and if the casing is full of water you may not even need a storage tank. I have a 2GPM well, no storage tank, and water a 1/2 acre of grass with it all summer long. I'll admit that it requires careful planning though:-)
If you go the tank/2nd pump route, I would get a pumptek, but I'd rely on it as a last line of defense. I'd run the pump wide open into your storage tank and then just use a programmable relay to give you X-minutes on to pump down the well , and then X-minutes off to wait for it to recover and repeat until the tank is full. I would avoid pumping the well dry. Throttling the well with a valve will waste some electricity. The pumptek will kick in and save the pump if you do happen to pump it dry.
Thanks to all for the advice. I'm only just learning about wells so this is all good info. The Pumptec unit seems like a good safety backup regardless. But, ideally, I wouldn't want it triggering routinely if I could help it. Obviously "throttling" the flow, and using the lowest HP pump possible, should help keep water in the casing.
One thing I don't get is why do you need a pressure tank BEFORE the underground tank unless it was already there before the underground tank went in? I assume the big tanks are not pressurized and would work best feeding at least a small pressure tank so every trickle of water didn't trigger the second pump? I assume the underground tanks have to be vented someshow? Are there issues with the water "going bad" (i.e. stuff growing in it, etc)?
It seems to me the ultimate would be a reasonably priced reliable way to monitor the water level in the casing electronically and you could set a low cut off point it would pump down to and a higher point the well would have to recover to before pumping resumed. But I'm probably dreaming for a reliable way to do that at 300+ feet (the depth of the well I'm concerned about).
Also, to ask another question, it looks like 1/2 HP pumps are only good for 100 - 300 feet at 1 - 2 GPM. Deeper wells (and total head) apparently need larger motors even at low flows? I'm fine with the output limited to 1 GPM or so to prevent frequent cycling or help reduce the chances of it running dry and tripping the Pumptec (or a similar device). But that means a big storage tank.
I'm guessing you can only go so big with a bladder tank before it's cheaper to go with an underground tank and second pump? Another plus, I'm told, is if the well does occasionally run dry seasonally, with a big enough underground tank, it can be filled from a truck.
You don't have to have a pressure tank before the storage tank. When sizing a pump for minimum GPM, be careful not to shave it too close and risk deadheading the pump. As long as the well continues to produce, it would not truly deadhead. If the level did drop and the well did not replenish resulting in the pump deadheading, the Pumptec might not detect it and so might not protect it.
A 300 foot, 6 inch dia. casing or bore hole could hold close to 300 gallons depending on static water level, so those metrics need to be factored in.
I would just pump directly from the well pump to a storage tank with a float switch. Then use another pump in the storage tank to send water to a pressure tank with a pressure switch for water going to the house.
If you throttle the well pump output to 1 GPM, the amps will drop. A Pumptec may not be able to tell the difference in amps of a pump restricted to 1 GPM from the amps of the pump when it is actually pumping air.
The Cycle Sensor can tell the difference between low flow and no flow. The amps actually read on the digital display for you to see. Without a throttling valve you can even control the depth of water at which the pump shuts off. You can see that the amps will drop as the water level in the well drops. So if you know the amps drop from 5 to 2.5 amps when the well is dry, then you can set it to shut the pump off at 3 amps, which is just before the well pumps dry.
My understanding of current draw vis a vis GPM curves is that it can vary by brand and model, that some pumps float the impeller bearing of each stage independently while others are fixed. I think it is for that reason Pumptec offers no assurance that they can detect a deadhead or near deadhead condition. It sounds like your Cycle Sensor may be a better choice with either style of pump.
We bought a house with a well that was producing about 1gpm. The well was 300' deep with a static level of 10'. That gave us almost 400 gallons of water in the well itself (6"well). We have been living in the house for a year and a half and never ran out of water for household needs.
We could not however water the lawn for too long and that is why we recently decided to deepen it.
All good info. Thanks to all those who have posted advice. I like the idea of detecting when the level is low in the casing but not yet to the point of the well running dry. Given what I know about motors and pumps, if a device can accurately monitor the current, that point should be fairly consistent. The Pumptec doesn't display the current but it is adjustable as to the "trip point" so it might be possible for it to detect when the well is merely low rather than dry.
The point about throttling the flow is a good one. I don't really know what to do about that. The same is true for sizing the pump. Obviously you don't want to size the pump so close it might deadhead when the well is really low. But the cost to have the pump be too big goes beyond just the pump cost. The wire size required to feed it adds up over 500+ feet (well depth plus distance to the house).
Whether or not the pump should be throttled is up for debate. If sizing a new pump, getting one with a lower GPM makes sense. A lot will depend on how many gallons of storage there are in the well and the size of the current pump. As I mentioned, not all pumps reduce current draw the same when throttled so I would plot the curve before deciding on a course of action.
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