Back pressure on new well pump

[fourwells]

This year my main domestic well began producing more fine sediment than usual (most of my neighbors have some amount of sediment.) The well was drilled in 2000. It is 660ft and the old Jacuzzi Sandmaster pump had been set at 360. I had a well/pump company pull the pump, inspect the casing, swab develop the well, and install a new pump with a sleeve over it. In the warm weather season the well produces about 6gpm after 12 hours of testing. Static is around 300ft and the new pump was re-set at 440. Other than the sediment, the water quality is good. Some tannins but other than that doesn't need much treatment.

During redevelopment of this well, the flow was throttled back to 5gpm at the well head and the well ran on a timer: 1hour on/1 hour off for three days. This was two months ago. The timer was removed and I have been advised to keep the throttle on at 5gpm primarily because the back pressure will reduce the amount of sediment I'm pulling and because the flow is less than my well gpm.

Since that time I have installed a 5,000 gallon storage tank and booster pump. The tank is filled with a mechanical float. For the initial fill I am using an irrigation hose/timer that flows at about 3gpm for 40 minutes. I noticed my filters would clog a bit after these fill sessions; this well is still used for domestic supply until my booster pump is wired next week. To address this I dropped each fill to 20-25 minutes and noticed improvement in the amound of sediment I'm pulling up.

Questions: 1. Do you agree that applying back pressure to the well pump would decrease the amount of sediment drawn up? 2. Would you argue that back pressure on the pump can increase the amount of sediment? 3. Is constant back pressure good for the pump long term? 4. Would it make sense that when I reduced the time for each of my fill cycles, I drew in less sediment (I've made the change a couple days ago)? 5. If Q4 is plausible, would it make sense to add a 240v timer to my well pump so that when the float is open, I only fill in say, 15 minute increments? (Theory being as well refills, the sediment would have time to sink.)

Finally, a thank-you is in order since this is my first time posting. I have four wells on my property (and one dry hole). No real experience with wells, or even plumbing for that matter until I bought this place 4 years ago. We've had a lot of water issues this summer and it is downright frightening. I appreciate all of you who contribute. I often find diagnoses/solutions in these forums, not just for the wells, but other things like replacing a recirc pump on a tankless heater. Most importantly I know I'm not alone! Thank you.

Looking forward to your ideas.

 

[Bannerman]

The lower flow rate maybe prolonging how long sediment will continue to be delivered to the surface, maybe forever.

Normally, a well will be developed by causing the pump to run continuously with the least amount of flow restriction, to allow it to pump out as much sediment and debris to the surface as possible. Disconnecting the drop pipe at the well head, will reduce the amount of flow restriction, thereby increasing the velocity of water flowing through the pump and being pumped to the surface. This will increase the amount of fine sediment drawn into the pump, which is then usually discarded into the field surrounding the well. Developing a well will often require only a few hours of constant pumping before the discharge becomes and remains clear, but sometimes, several days of continuous pumping will be needed.

You didn't state how deep the casing is installed, nor the depth of the inlet screen if utilized.

If the water is entering the well above the pump location, such as through an inlet screen located above the pump, sediment entering with the well inflow will also be dropping from above the pump, allowing the sediment to be drawn into the pump whenever the pump is operating.

By properly developing a well, the fine sediment particles that are passing through the inlet screen, will eventually reduce, allowing larger sediment particles that can't pass through the screen, to pack around the outside of th3 screen, thereby acting as an additional sand filter to further prevent smaller sediment particles from within the surrounding soil, from even coming into contact with the screen.

Pump's are designed for continuous duty, so there is no harm if runing 24/7/365. Restricting the flow output will not harm the pump as long as at least 1 GPM is being drawn into the inlet, to provide cooling flow over the electric motor. The flow inducer shroud now installed, will help to ensure cooling flow over the motor, even if the flow rate is only 1 GPM.

Reducing the flow rate by restricting the outflow, will be equal to what will occur when the water level in the well drops lower than the 300' static level. While most consider increasing flow restriction will cause the pump to work harder, in actual fact, the opposite will be true. Since the pump will be moving less than it's maximum flow capability, it won't need to work as hard and as a result, power consumption will be usually reduced.

 

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[fourwells]

The well casing is installed to 660 feet. Perforations at 200-220, 320-340, 420-440, 480-520, and 580-660. Each perf is .032" and the filter pack is 1/4 minus.

Thanks for your explanation of the effects of restricting flow. Count me among those who speculate that adding back pressure would cause the pump to work harder. My logic is that it would have to overcome the additional pressure therefore suction would be stronger at the end of the pipe than it would be unrestricted. Further, the added pressure will cause greater suction at the end which could also cause more sediment to stir, suspend, and be drawn up.

In your explanation I could see the restriction giving the pump some "free" pressure to use so that it wouldn't have to build it up on its own to meet the demand. Am I interpreting correctly?

If the real concern is keeping the motor cool by passing 1GPM I wouldn't need to be concerned under my current conditions. I believe the pressure tank is about 30-35 gallons drawdown.

Re: the well (re)development, I believe they did develop the well directly from the head without restriction for awhile. It was a Friday and in the afternoon they took away the probe, set the restriction at 5gpm, and set the timer. Came back on Tuesday to put things back together. Two weeks later I needed a well yield test for a building permit. That was also run unrestricted. After the first couple hours, only trace amounts of sand/sediment were detected. Just another data point to throw out there.

 

[Valveman]

The real problem is the 1/4 minus gravel. I would have used much smaller gravel, something just larger than the .032 slots. I might have even use .020 slots instead. But .032 should be small enough, just need smaller gravel. But it is too late for that. As was said developing the well usually means higher flow rates. I don't think the sand will even come up 1" or 1.25" pipe as it is barely at 1 FPS. The water is coming up so slow that in the 6-7 minutes it takes to get to the top the sand just settles back down to the bottom. I think you can still develop the well if you run it wide open until it pulls the well down, shut off the pump for a time, and do it all over again. You will need a dry run protector like the Cycle Sensor to keep this going for hours or days if needed.

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