Another well question

[the old grind]

Simple version: Pump specs are either/or. Max flow will be at min pressure and vice versa, and both are rated at zero lift (suction height). Actual lift is between static height and the pump. Intake placement should be well off the bottom but remain well below draw-down height. When the latter becomes ~25' or so, cavitation & damage are imminent. The suction hose/pipe might best be sized to the pump's intake port.

I use a HFT 6hp/2" to draw water from the pond with a 2" intake and discarded 1 1/2" fire hoses adapted (barb/clamp) to the slightly different std 1 1/2" (bushed-down) outlet thread. It'll fill a 55 gal drum in < 1min. I get good flow to stands of trees I've planted with 100-150' of the fire hose. This is to flood an area vs running sprinklers etc. Before that I'd use a generator & sump pump in a weighted 5 gal bucket, to draw to the 55-er & dip as needed. That got old fast & I went to the gas pump, though the pond was there & this won't help the OP.

IMO the 8hp/3" pump would not be a good choice if drawing from a 4" well regardless of how deep or how fit that is. Expect it to draw the well down way too quickly and be difficult to predict/control suction with output restrictions. A smaller pressure pump (HFT) & a generator might get you there for a while but would have to be taken to or left on the site.

The 'shallow well/booster' pump (HFT) might work, handier if outlet hoses can be left in place. Trouble with well pumps is that by using split phase motors they demand huge generator capacity to start. A 3k gen might not start a typical 1/2 - 3/4 hp well pump as one would expect by its (motor's) rated amperage, tho' internally (Honda) vs externally regulated (HFT, many others) would do better per rated kw. Too bad the low-flow high-pressure pump I'd recommend for sprinklers doesn't have a gas version. Running electricity way out back would require too heavy a gauge wire ($$) to carry adequate current the distance.

It'd help if we knew the size of the garden to be irrigated, & this mish-mash might be irrelevant considering that, but this could be a tough one to pull off with even the best help. I'll leave the bigger details/explanations to those who've managed using a similarly remote water source. btw: sure hope raccoons don't eat/flatten that corn before the harvest. (BTDT)

 

[rmorey]

What you need to establish is the well's recovery rate (gpm). That is the amount of water that enters the well. This will determine the size of pump you need. If you exceed that size (gpm) the well will drain and burn out your pump. If you use a pump that stays below that level, you will always have water.

The pump will be rated by gpm so get one that is rated below the well recovery rate.

Determining the rate of recovery of the well is simple, measure the depth of the well, then use your mega pump to empty the well. Time the recovery for an hour. "X" number of feet of recovery per hour divided by 60, is "Y" feet per minute. A 4" well has about 2/3 gallon per foot. "Y" feet times 2/3 gives you an approximate gpm inflow. Certainly good enough to determine required pump size. Hope that helps...

 

[Stimw]

I'm up in St. Johns County, my water table runs 2-6'. 16' seems pretty low. ?? Might even be artiasn well with low table.
A 4" casing is pretty big and should be a deeper well. I would drop a weight on a string and find out how deep. (Neighbor's rock well is 600')
For a drop pipe I would use 1 1/4" PVC with a 5' or 10' PVC wellpoint (sold at Ace, HD, Lowes) to filter so sprinklers don't clog. Drop it 30'-40' down. You don't need a foot valve with our conditions.
With that size pump you might need to run multiple hoses even at idle.
I bought a 2' Gas pump at HF for under $200. on sale that does a great job! I used it to wash down a well and to clean out sediment in another and it pumped a lot of water even at a fast idle.
Also well needs to be AT LEAST 100' from septic system to be legal!