water well issue

[RustyShackleford]

Our house uses a roughly 100-ft deep water well (6" diameter) with a 1/2HP submersible pump. It's the kind without a separate control box, since there are only two conductors (plus ground) going down the shaft.

The water supply has become intermittent. It's most noticeable when doing things like filling the bathtub. I believe I've narrowed it down to something in the well itself, because I can measure 240vac right at the well-head, but near-zero current draw. When the well does kick back on, it's drawing about 15 amps (way too much steady-state current for 1/2HP pump); but then it quits again before reaching the pressure switch cutoff level. I guess when water usage isn't that high, it comes on again (once or more) to hit the cutoff level, and we never notice a problem.

I'm thinking maybe the 15-amp current draw is causing a thermal overload and shutdown, but then it recovers fairly quickly since it's submerged in water. Is this a normal failure mode for these pumps ? A knowledgeable friend suggests maybe the startup torque of the motor is rubbing the wires against the side of the well, which I suppose could be responsible for the excess current draw (maybe I should check if any current is flowing the ground wire ?); but why would that make the pump shut down, unless it's just starved for current. He also suggests a loose connection somewhere could cause the 15-amp draw, but that doesn't make sense to me. And anyhow, that shouldn't cause the pump to overheat either.

Penny for your thoughts.

 

[RustyShackleford]

Local guy said "sometimes the nipple in the pressure switch will get stopped up and you will get zero water pressure". Does that any sense ? I guess I'll just replace it, 'tis 37 years old.

 

[gthomas785]

Yeah, I would guess the pump bearings are worn out and dragging causing it to draw excess current which heats it up until it goes off on thermal. Very common for motors to die this way. Time to pull the pump and replace it.
Do check for a ground fault, but rubbed out wires would be causing a constant leak (not intermittent as you're seeing) and would most likely be tripping the breaker.

The nipple clogged thing is a common problem, but doesn't explain what you're seeing. That would cause the pressure switch to stick either on or off. In which case the pump would either run continuously or not at all.

 

[RustyShackleford]

Not sure what pump to get. I like the notion of Grundfos "soft start", for better compatability with inverters for backup power. I like even better the idea of a 120vac soft-start type. Dunno if that's workable or not. If I upgrade the conductors from 12awg to 10awg, the round-trip (400ft) resistance is about 0.4 ohms.

The original pump was a Gould 7EH05, which apparently is 1/2HP and 7gpm (it was replaced after a lightning strike in '93 and I don't know what was used there). The Grundfos I find with similar specs is:

10 SQ05-110

Groundwater supply from 3" or 4" wells

product-selection.grundfos.com

... which oddly is a 1HP pump. But its current draw is 12 amps, which works out to about 5v of droop, which is about 4%, which is probably too much. Also, I dunno if the fact it's "soft start" and the operating current is 12 amps means it'll never (e.g. on startup) draw more than 12 amps. So that's 5v (4%) droop; but since the "rated voltage" is 100-115v, maybe it's ok.

 

[gthomas785]

Did you calculate the load to size the pump correctly? The old pump could've been undersized and contributed to its failure.

Also, did this start happening after you replaced that rusty nipple? The clogged pipe could've been reducing the load on the pump enough to mask this issue or even prevent it previously.

Generally, higher voltage and lower current is easier on motors, so only get a 120v pump if you absolutely need it for generator applications.

 

[RustyShackleford]

Did you calculate the load to size the pump correctly? The old pump could've been undersized and contributed to its failure.

The first two pumps (original Gould 7EH05, and lighting-strike replacement only called 1//2HP in invoice) were done by contractor without input from me.

As far as sizing the new one, as I said the well is 105-ft deep (according to bill from OG plumber), and it's about 100-ft (horizontal) from well-head to pressure tank. That works out to probably 125-ft of effective head. Except, if the water level is above the pump's location 105-ft down, doesn't that reduce the head ? I have no clue how deep the water level is. The old pump was spec'd for 7gpm, which seemed ok, but 10gpm seems like a better target. So looking at the attached document from Grundfos (on their soft-start series), it appears the 10SQ07-200 (page 38) is probably the ticket. It is a 3/4HP unit, but with "soft start" and its 8.4-amp rated current, I think my existing wiring can handle it. If you look at the performance curves earlier in the doc, it appears a 1/2HP 10SQ05-160 (page 14) should be fine, but if you look at that same sizing chart (p.38) you can see that it's no good; evidently the performance curves don't account for the fact the thing is working against the pressure building up in the pressure tank. (I'm assuming I need to use the 50psi row in the table of p.38, if I have my pressure switch set at 30-50psi).

Also, did this start happening after you replaced that rusty nipple? The clogged pipe could've been reducing the load on the pump enough to mask this issue or even prevent it previously.

Yepper, it started happening right after. Pretty big coincidence, huh ?

Generally, higher voltage and lower current is easier on motors, so only get a 120v pump if you absolutely need it for generator applications.

Yeah, scratching that idea. Gonna have to spring for a 240vac inverter if I plan to run the thing off backup batteries. But with soft-start, and the power-factor is 1.0 (how the heck do they do that ?) it shouldn't need to be that big an inverter.

Also, @gthomas785 (thanks MUCH for your help), you said you think my pump is experiencing a very common failure mode. Would you hazard a guess as to how long it can limp along this way before I'm totally dry ?

 

[gthomas785]

I did not double check your calculation but at a quick glance 3/4 HP seems reasonable.

To get the pumping depth, you'd have to draw down the well for a while before measuring and it can vary depending on seasons, neighbors water usage, and all that. You'd be very safe to assume the pumping head is the same as the pump depth. The head loss from piping can be calculated with online head loss calculator like this: https://www.omnicalculator.com/physics/friction-loss
As you'll see, the friction loss increases almost quadratically with GPM.

 

[gthomas785]

No idea how long your pump will last.
If you're that kind of person, you could collect some trend data on current draw/gpm and see if it's getting worse over time.
If you have a valve before the pressure tank, you could try valving down the flow rate to make it a little easier on the motor.

 

[RustyShackleford]

I did not double check your calculation but at a quick glance 3/4 HP seems reasonable.

Previous was 1/2HP, but I don't see much harm in possibly oversizing (since I'm pretty sure the electrical can easily handle it).

You'd be very safe to assume the pumping head is the same as the pump depth.

Which definitely says 3/4HP.

The head loss from piping can be calculated with online head loss calculator like this: https://www.omnicalculator.com/physics/friction-loss

Thanks for that. Looks negligible for me, maybe 15ft.

 

[gthomas785]

Previous was 1/2HP, but I don't see much harm in possibly oversizing (since I'm pretty sure the electrical can easily handle it).

If you oversize by a lot, you could get rapid cycling, which could shorten the pump's life. However, if you have that situation you can throttle back the flow and decrease the effective HP of the pump.
In this case I can't see much going wrong just going up by 1/4 HP.

 

[RustyShackleford]

Nice chart here for the sizing stuff ...

Clearly the crux of the issue for me deciding between 10SQ05-160 and 10SQ07-200 is whether I assume the static water level is at pump depth (100ft) or if it's substantially higher, maybe 50ft.

 

[RustyShackleford]

If you oversize by a lot, you could get rapid cycling, which could shorten the pump's life. However, if you have that situation you can throttle back the flow and decrease the effective HP of the pump.

How would I throttle back the flow ? Valve between pump and pressure tank ?

Another option would be to get a bigger pressure tank, no ?

 

[gthomas785]

How would I throttle back the flow ? Valve between pump and pressure tank ?

Another option would be to get a bigger pressure tank, no ?

Yes, and yes. It really comes down to how much water you use, and your peak flow demand.

 

[RustyShackleford]

So I just replaced the pressure switch, because why not, it's 37 years old and I want to rule out everything but the pump. Glad I did, because some of that corrosion from that non-brass nipple that I replaced the other day had worked it's way up the nipple that goes to the pressure switch; I don't think it was messing with the switch yet, but probably planning to.

 

[zrock]

I would not be going down to a 120v pump.. thier is a reason most installations are 240 its much easier on the pump. Starting up a 120v pump with th head it has to push puts a lot of strain on 120v and thn on the pump

 

[EbS-P]

Eventually you will want 240V backup for hot water or AC. Running Batteries or generators.

 

[RustyShackleford]

Thanks, I've pretty much given up on 120vac, for voltage-drop reasons alone (the pump I want to use take 8.4 amps at 240vac, so even if I spring for 8awg wire, the voltage drop is un acceptable). With these new soft-start motors though, I'm not so sure the argument about 120vac being harder on the motor holds anymore.

Our power is pretty reliable here, and we heat with wood (duh), so I'm happy if the well pump is the only 240vac load I can run. But having it be soft-start (with a power-factor of unity) makes that a heck of a lot easier.

 

[RustyShackleford]

Well, today was the day the music died ... I mean, the pump died. Called a family enterprise my friend rec'd and they came on out within hours. The non-running pump was drawing 23 amps !

They replaced with the 3/4HP option (Grundfos 10SQ07-200), said it's the main option they keep in the truck because it works for almost everything in this area, Total $1800, not too bad I guess - the cheapest I could find the pump online was about $1000, and another $100 or so for new wire (they said the pipe looked fine).

 

[RustyShackleford]

One thing: the water is muddy (and of course full of chlorine from the disinfecting). They said "let it run 10 minutes". Will that really help that much ? Doesn't it make more sense to just let it run overnight so the dis-lodged silt sinks below the level of the pump ?

 

[gthomas785]

One thing: the water is muddy (and of course full of chlorine from the disinfecting). They said "let it run 10 minutes". Will that really help that much ? Doesn't it make more sense to just let it run overnight so the dis-lodged silt sinks below the level of the pump ?

10 minutes at 10 GPM is 100 gallons, probably close to the volume of the wellbore
10-15 mins should flush it out.

Edit: congrats on the new pump

 

[RustyShackleford]

Thanks for all your support !

 

[bigealta]

Well, today was the day the music died ... I mean, the pump died. Called a family enterprise my friend rec'd and they came on out within hours. The non-running pump was drawing 23 amps !

They replaced with the 3/4HP option (Grundfos 10SQ07-200), said it's the main option they keep in the truck because it works for almost everything in this area, Total $1800, not too bad I guess - the cheapest I could find the pump online was about $1000, and another $100 or so for new wire (they said the pipe looked fine).

$1,800 that's cheap. I paid over 3K for mine at my rental house last year. I think it's the same pump. Well is 140-160ft deep. They replaced the pvc 10ft? sectioned pipes and wiring with new wire and 1 continuous piece of pvc? pipe from a roll.

 

[RustyShackleford]

$1,800 that's cheap. I paid over 3K for mine at my rental house last year. I think it's the same pump. Well is 140-160ft deep. They replaced the pvc 10ft? sectioned pipes and wiring with new wire and 1 continuous piece of pvc? pipe from a roll.

Oh yeah, the pipe is gonna cost a bit, and you're half again as deep.

 

[crstrode]

Well, today was the day the music died ... I mean, the pump died. Called a family enterprise my friend rec'd and they came on out within hours. The non-running pump was drawing 23 amps !

They replaced with the 3/4HP option (Grundfos 10SQ07-200), said it's the main option they keep in the truck because it works for almost everything in this area, Total $1800, not too bad I guess - the cheapest I could find the pump online was about $1000, and another $100 or so for new wire (they said the pipe looked fine).

With a Grundfos in the ground, you can rest easy. I worked for years as an Environmental Restoration Engineer, and Grundfos is what I used for dozens of pump-and-treat groundwater applications. They were all 3-phase, and I always specified the number of impellers depending on the depth. You will be good to go for life - unless your age is less than the age of my socks.

 

[RustyShackleford]

With a Grundfos in the ground, you can rest easy.

Yeah, I think it's common knowledge at this point; the people who fixed mine don't bother with anything else.

I'm also happy about the fact that it's going to be a lot simpler to be able to pump water during power outages. Still not sure the best way to get 240vac. A 120->240vac transformer dedicated to this one circuit ? An autotransformer and put split-phase into my load center (via the generator inlet) ? (Right now I put the output of a 120vac inverter to both sides of the panel, which of course means the 240v loads see zero volts). Find an affordable 240vac inverter ? Whatever I do, it's gonna be a LOT easier now.