Water Well System
Contents
Introduction
- We have dug the well below and are now pressurizing the water and burying lines for winter, zone 4 in Missouri.
- The well is 33' deep to silt, and as of December 2012 it is 13' deep even after extreme drought.
Design Rationale
- 3/4 acre pond up hill feeds agricultural operations
- Tee between rural and well water selects between sources for HabLab
- Buried rain barrel holds T - DIY manhole
- 3' below ground
- wooden top with additional layer of insulating pinkboard (polyurethane)
- Slits cut into the sides using a saws-all for sliding fittings up and down, scrap plastic then added to prevent dirt from falling in the slits
- Drainage holes cut into the bottom using 2" circular bit on a power drill
- Rural water for backup
- very high water pressure puts our off grid fittings to the test, some of them fail
- treated water, contains chlorine
- Normal operation: well water
- Well with 1000-3000 gallon per day recharge rate is main potable water source for facility
- 17' of vertical height in 40" well casing provide 52 gallons per foot, total of about 1000 gallons of storage
- Scrap rebar holds safety line to pitless adapter and pump in case pipe connection fails
- Pressure tank located next to well within a basin
- Both basin and pressure tank spray painted black to prevent corrosion
- Pressure switch and pressure gauge located on pressure tank
- 230Vac power line comes from workshop, 90' away connected to both the pressure switch and pump (3 submersible splice kits connect pump)
- Power line buried about 1' down with Trencher
- Water lines buried 3' throughout with Backhoe
- Lead free brass fittings - about the same price as standard fittings, but we have to mail order them
Review Questions
- Can pressure switch and gauge be located in pit right next to well? Will it corrode due to moisture? Typically, the pressure switch is located on the pressure tank in the house, but here, our power system is located in the workshop. The workshop power feeds the house at 120VAC. The submersible pump is 240VAC. We would have to run another 240V line to the house and then to the well, which would add another 500' of wire to support the well - by extending our 240VAC line to the house. Instead, we can run the 24oV power directly to the well from the workshop.
- What gauge wire do we need to run to the pressure switch for the 240V pump if the total wire run is under 100' from workshop?
- Should we get a 30/50 PSI pressure switch or 40/60 PSI switch?
Expert Review
Andy Halbert, Well Driller
Putting the pressure switch next to the well without a pressure tank will cause some issues. To keep the math simple we'll ignore the elevation difference between the well, shop & hablab. We'll also ignore the actual flow of the pump will vary based on the total head against it and just use the nominal rating of the pump.
I'm guessing you have or are getting a 1/2hp 10 GPM submersible pump, so when it is running you will have 10 gpm that has to go somewhere, most of the time you don't use that much water, so the extra ends up in the pressure tank. The pipe between the pressure switch & the pressure tank as drawn is 240' of 3/4" pipe. The friction loss on the pipe at 10 gpm is about 40 psi, (use this online calculator http://www.freecalc.com/fricdia.htm ). What that basically means is if the 3/4" pipe was just open ended at the hablab and let run on the ground, it would take 40 psi of pressure at the well end to push the 10 gpm through the pipe. What that also means is if you have a 30/50 pressure switch at the well, you turn the power on and the pump will start, the pressure switch will turn off the pump when there is 50 psi at the well, meanwhile, there is only 10 psi at the hablab pressure tank location because of the pipe friction, when the pump turns off, the water system goes to a static water pressure state (pipe friction not a factor in a static system), then the pressure switch senses 10 psi because that is the static pressure on the system so it turns the pump back on, and thus you start "short cycling" the system. Depending on different factors, the actual pump cycles can be less than a second and the pressure switch will chatter. Eventually after several cycles it will get enough pressure on the system to stop cycling, but when you use some water it will start the cycle over again, and that will destroy a pump fairly fast.
For the sake of simplicity I would just get the largest pressure tank you can fit in the 2' culvert with the pressure switch. Set the tank air precharge at two psi lower than the cut in pressure of your pressure switch. I would use a 40/60 pressure switch, but that is a personal preference and there is nothing wrong with using a 30/50.
Also, you may want a Franklin Electric PumpTec to protect the pump when the well is pumped dry. It watches the current draw of the motor and turns the pump off when it sucks air then waits a while for the well to recover and turns the pump on again automatically.
In certain circumstances we use a "cycle stop valve" with a small pressure tank, but with your off-grid power system I don't think I would use one. A cycle stop valve is also NOT compatible with a Franklin PumpTec.
The Franklin AIM manual (http://www.franklin-electric.com/media/documents/M1311_60_Hz_AIM_Catalog.pdf) is the go to source for information on submersible motors. Single phase wire sizing is on page 11, for a 230v 1/2HP pump you can have up to 400' of AWG 14 wire, or up to 650' of AWG 12 wire. In actual practice, we generally don't use wire smaller than AWG 12, but it would work.
Regarding Pump Vibration and Fittings
The pump shouldn't really vibrate if things are working correctly. There may be a slight "humming" sound from the pipes but no major vibrations. Generally we don't see any issues with pipe fittings coming apart. The pump will jerk downhole from the toque when it turns on and can also have a jerk when it shuts down. The pump startup jerk is can cause issues with the wires rubbing against the well casing and eventually rubbing the wiring insulation off, so tape the wires to the drop pipe in several places.
If it was us, we would use 1" 160psi poly pipe to hang the pump in the well. The pump will most likely have a 1 1/4" female pipe thread, and I'm guessing you have a 1" slide pitless, but you could have a 1 1/4".
For best results/reliability use brass insert fittings (hose barbs), and brass bushings. Avoid insert fittings made of gray poly, white nylon or any type of plastic. Also avoid plastic threaded bushings.
Don't forget you will need a 5 or 6' long steel pipe to screw into the top of the pitless to use as a handle when you set the pump, then you remove the "handle pipe" before you put the cap on the top of the well.
Regarding Electrical
use a "submersible pump splice kit". I think menards in St Joseph has them in stock, or if you're not in a hurry, I could mail some to you. They use an in-line crimp connector, and then have a special heat shrink tubing that goes over the splice. The heat shrink tubing has an adhesive sealant that seals up when heated, the tubing also usually has a shrink ratio of 3:1 instead of just 2:1.
We actually crimp, then solder the crimp connector on all the submerged splices we make, then put the heat shrink on them. Most people don't solder like we do, we just like to eliminate as many failure points as we can.
