I'm embarrassed to note that it was two week ago when I asked if the well depth measurenmt problem was solved, and y'all answered right away that you'd be interested in what I was doing to solve a similar problem. Shucks -- got real busy here for awhile I guess ...
My solution is for a well that's not so deep (265 ft), and I haven't done it yet, but am about to make a first attempt at it, and will hopefully have it in sometime next week, if all goes well#### as planned.
I'm figuring on using a Freescale pressure sensor (MPXH6400A), which will measure up to 58 psi absolute. If I subtract about 11 psi atmospheric pressure (at 7200 ft), I get a useful range of measurement of 47 psi, or about 108 feet. My static depth has never been better than about 160 feet, and the pump is located at about 190 ft, with 70 un-used feet of hole below that (which I'd like to use). So if I put the sensor at or just below the pump, I'll be able to measure the entire range with this one sensor. One reason to choose this sensor, rather than a higher pressure one that I could put at the bottom, is that it comes in the really tiny package that I can fit inside a 1/2" copper pipe to use as a housing.
The reason my pump isn't nearer the bottom is because there's something wrong with the casing near the 190 ft level. I don't know if it's collapsed, offset, damaged, or what. The well was drilled in 1971, and I'm the second owner, with no way to find out what happened. Somewhat shoddy, low-bid job, I suspect. Anyhow, my goal with the sensors is to maximize production of the current well such that I don't have to dump 6 or 8 grand into drilling another hole. I may eventually need to, but by then, city water will likely be available. (It's getting close all the time. We used to be 15 miles out of town, and now it's only about 1/2 mile away.) We only now have occasional trouble since we've just put in a bit of lawn in the back, and have expanded the garden. We really only have trouble when the wife wants to do three loads of laundry on a Saturday morning, just after the lawn and garden have been watered (all on timers), and guests have arrived for the week. I guess it's an old enough well that you can't expect recovery to be great anymore. Maybe I need to investigate getting it flushed or washed out somehow to improve it. But I also know the water table is dropping a bit here, and this being a fairly shallow well anyhow, I might have to bite the bullet and replace it. When it does go almost dry, the extra turbulence busts loose a lot of sand and cloudy kind of crap, but it clears quickly if we let it alone for awhile. I've put a sediment filter on it -- which appears to be nothing compared to the level of filtering you've had to do.
So, you might ask, what does any of this have to do with your well? Nothing maybe, in that I seen you've already considered the sensors from Freescale. But I do have this to add -- I note that the absolute maximum pressure for these sensors is four times the rated pressure. If you look over what they tell you about the parts, you find that the output saturates or hits the supply rail, and of course won't put out anymore than full scale. That's understandable, but then why is the maximum pressure four times the max operating pressure? I asked them, via email, what happens when you exceed this pressure, and then bring it back to within range. They replied that the burst pressure is two to three times the max allowed pressure, so they've really left themselves a lot of margin, even at 4x operating prssure. Basically, it would start to work again when the pressure drops to within range, but there was some fine-print disclaimer wording that implied they won't guarantee that it will work if you run it too high. (I guess I should go look it up so I know *exactly* what it says.) I suppose they don't want to guarantee it, because then you could hold them to it, but as long as it doesn't bust the die or blow the case apart, I'd bet it would work great. One could test this on the surface easily enough -- hook the 150 psi sensor to a small tank and blow it up to 300 psi, and come back in a week and test it in normal range to see if it survived. The idea then, is to use two of these, one set where the pressure would be almost full scale at your highest expected static depth, and one below that. BTW, if you suspect the water coming in is somewhere near the 400 ft depth point, you could be cautious and make it easy on the sensor by setting it just below this point. That way, you can pump only a measured length of time beyond the point where the lower sensor goes dry, and know that you weren't going to run the pump dry. So anyhow, you'd have two sensors, one of which would be giving you good data. If you could locate them close enough together, they'd both put out valid values when the depth was right, thereby validating the other's reading.
The price is even right for these sensors, in that Freescale seems happy to send out samples of these. One minor problem, however, is that they're only good for measuring dry air. The solution is to use a short head tube filled with silicone oil, with trapped air above the oil. This stuff is pretty harmless, so you don't need to fret having a few drops in your well. Several ways to be sure it doesn't escape. I've got a sample of this stuff, which I'd be willing to share with anyone doing similar tinkering. My sample is pretty thin (50 centistokes viscosity), but with a fairly fine capillary tube it should work fine.
That's the idea, anyhow -- hope it helps. With my casing problem, eventually, I hope to get a very thin submsersible camera to chuck down my well to have a look around at what the trouble is at the 190 ft level. Then I'll have to figure out if I can get past it with a slim-line pump, wheter some kind of repair might be possible, or if I have to just re-drill the thing. I'd sure like to have more capacity at times. Anyone here know of a submersible camera as small as 1/2" diameter, including light source? Color preferred, of course. I might be able to use something a bit bigger, but I've got 5" casing and a pump that's just under 4", so am not sure I can count on slipping much more than 1/2" past the pump, particularly where the problem is. That reminds me: I meant to mention that I'm planning to use a long length of poly-pipe to send this thing down the well, so that there's little chance it could get hooked on something. I know I can get 1/2" poly in 250 ft rolls. Not sure how I'd join two of them to go 500 feet, however. Tricky at best. Looks like maybe you could use a camera too, for finding out what got stuck down there a hundred feet (or did you get that extracted already?).
Sorry this got verbose -- hope it doesn't choke when I try to submit it. I really didn't intend to double the length of this thread in one swell foop ...
S^2
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