I'm NOT asking for a recommendation for particular pump. I want to know HOW to choose between pumps.
My understanding is as follows:
A: The pump has to be sized for both the pressure you want at the output, and the volume you want.
B: Pressure needed is output pressure + ~1/2 the drop between the output point and the water level in the well.
So: For example. The water level in the well is 60 feet below the top of the well. The house is 20 feet above the top of the well. I want 50 psi at the house. I need a 50 + 1/2(20+60) = about 90 psi.
In fact I want a bit above this, as in use that 20 feet will increase under load.
I can also convert this to head by roughly H + 2P So in this case H=60+20 and 2P=100, so I need a pump that produces a total head of 180 feet.
Again I want some cushion above this, as a 180 foot head pump would push no volume at this pressure. More detailed planning requires reading the pump curves for the individual pump.
This all background showing that I'm not completely ignorant and am not comparing apples to aardvarks.
So on Amazon.ca we have:
OrangeA Deep Well Submersible Pump 25GPM Stainless Steel Deep Well Pump 0.5HP 150ft head Submersible Well Pump for Industrial and Home for $149 including shipping.
Hallmark Industries MA0343X-4A Deep Well Submersible Pump, 1/2 hp, 230V, 60 Hz, 25 GPM, 150' Head, Stainless Steel, 4" $203
Red Lion RL12G05-3W2V 1/2-HP 12-GPM 3-Wire 230-Volt Submersible Deep Well Pump with Control Box $409
That controler box is a sneak — not all list it.
I'm unlikely to buy a pump off of Amazon. At least on the Canadian site they don't list either Gould or Franklin, which are the two most common names beside Red Lion.
But what features do I look for in a pump?
The present pump has been in use now for at least 20 years. During the growing season it's running 24 hours a day. It's starting to wear out. I've had to crank back the cutoff pressure for the pump to actually turn off. It's now cuts off at 45 psi. I don't need to replace it this minute. Next irrigation season starts in April.
What do I look for when choosing a pump?
- Stainless steel casing.
- Plastic vs metal impellers?
- 230 v (Pump is 300 feet from house.)
- Automatic low water shutoff?
- Thermal protected motor
Is Variable Frequency Drive worth it?
Best Answer
Stainless steel casing. Only if you think there is something corrosive in your water. As a general rule, a submersible pump is under water all of the time. Rust requires oxygen, so unless you constantly pump it dry and expose it, the stainless can be a waste. But it does help with other corrosives. 20 years is a long time, was that pump stainless?
Plastic vs metal impellers? Plastic is cheaper, but ANY tiny amount of possible grit chews it up really fast.
230 v (Pump is 300 feet from house.) Absolute minimum; don't even consider 120V.
Automatic low water shutoff? Absolutely, unless you have some other means of doing that.
Thermal protected motor. You are required by code to have running overload protection for the motor. Using a thermally protected motor qualifies. If you get one without it, you must add a thermal overload relay to your controller.
Is Variable Frequency Drive worth it? Maybe. Is variable volume important to you? In a pump like this, if you pump at full volume and turn it down with a valve, you are wasting some energy in that process. Using a VFD to lower the flow accomplishes the same thing while using significantly less energy in the process. But if you are NOT varying the flow on a regular basis, then the losses in the VFD will actually cost you MORE energy in comparison. So it depends on what you want to do with the irrigation system. A side benefit to a VFD however is that you can use it to convert your single phase electric service to run a 3 phase pump. The advantage there is that the pump is more reliable in the long run, there is no "start capacitor / run winding" in the motor that must be switched in and out.