Alright, hold on to something, this is going to be a long one.
Since I finally got my pump freed, I now have the opportunity to overthink things and fix them until they break.
This will be the first of three posts, since apparently everything at once is a bit over the character limit...
The Well
My well is in the coastal plain of Maryland, so I expect mostly sediments on the way down. I won't go into the full water composition, but notable are extremely high iron and manganese levels, and a pH of 5.6. The state apparently lost records from the period when the well was drilled, but they believe it was in 1962. The casing is 4" Schedule 40 PVC in 20' sections. Strangely, measuring the distance between joints has most of them at almost exactly 20', but the second and third sections down measure over 4" too short. Maybe they were damaged on the ends and cut before installation? The total depth is about 83.4 m (273.5 ft), although there may be a layer of sediment that stopped my measurement short.
Regarding the condition of the casing, I found that several sections are very... bumpy? There is also a damaged section at around 50 m (165 ft), right next to where the pump previously sat. That probably isn't coincidence, and I'm guessing the pump must have overheated at some point and weakened the PVC. I couldn't get a great view, but it almost appears cracked. The pump was stuck on this section, so I'll just reinstall right above it. I'm considering trying to get a length of 3.5" PVC pipe into the damaged section to reinforce it, but it's difficult to assess the situation under water with such high turbidity.
Here's a video trying to show the damage (on the left): https://streamable.com/4u5s9e
And here's a bumpy part of the casing compared to a normal one:
The static water level is around 39 m (128 ft). Drawdown levels will have to wait until I have the pump back in. I measured the water level with a camera at the end of a distance-marked fiberglass cable, but also tested echo distance measuring using my phone to emit a signal. A phone could also be used to record the signal and echo, but I used a microphone connected to my laptop so that I could skip transferring the recording, and probably get a higher quality recording. I used Audacity to measure the time between signal and echo.
Here's what three pulses and their echoes look like:
The pulse itself is very clearly defined, but the echo is a bit dispersed. I used the the first point where the echo became distinguishable from the noise background as reference. If we assume the timing can be measured to within a millisecond, that corresponds to a max distance measurement error of about 17 cm (6.7 in). Things like pressure and humidity can influence the speed of sound by a fraction of a percent, but more significant is temperature. An estimate is fine here though, since the change in air temperature from 10-25 °C (50-77 °F) is less than a 3% change in the speed of sound. The well's water temperature seems like a decent estimate for the air temperature. There are plenty of online charts and calculators that show the speed of sound for a given temperature.
Anyway, for my well, I estimated 342.3 m/s as the speed of sound. I measured the delay for five echoes to a precision of 0.5 ms and got 0.2295 s for all five, so repeatability is very good. One thing to note is that despite me setting the pulse frequency to 10 kHz, the highest amplitudes of the signals and echoes were well below 1 kHz. The timing was the same when isolating to these frequencies, so I don't think it matters much, but it might be an indication that 1 kHz would be a better choice than 10 kHz.
That works out to 342.3 m/s * 0.2295 s / 2 = 39.28 m (128.87 ft) measured acoustically, compared to the 39.09 m (128.25 ft) measured directly. Assuming my direct measurement is correct, and assuming the water level didn't change in the hours between these two measurements, that's less than a 0.5% error. Not too bad. If we assume my timing and my direct measurements were correct, that would mean an actual speed of sound of 340.7 m/s, which would relate to a temperature difference of just 2.8 °C (5 °F) from what I estimated for my measurement.
Making an app that does all of this at the press of a button wouldn't be too difficult, I'll probably give it a try when I have a little more free time. Just don't go dropping your phone down a well. I also plan to create an acoustic distance sensor to install ~120' down to give me continuous monitoring of levels over time, but I don't have time for that just yet either.
The Cap
My cap is from MAASS Midwest, model WTCC-4. I wanted something that was aluminum (or at least, not plastic/steel/cast iron), vented, and had a connection for electrical conduit. This fits all of those requirements, but execution could be a bit better. I'm happy overall with it though - it does its job and was fairly cheap.
Some thoughts for improvement:
1. The casting isn't as flat as I'd like to see for the mating surfaces, but honestly it's as good as it needs to be considering this is a vented cap. The opening for the casing is also much larger than it needs to be. It has a screw to tighten against the casing, but a tighter initial fit would have been nice (or having three screws for tightening to a more centered position.) I cleaned up the mating surface of the upper section to have a continuous flat path along the seals, and will do the same for the lower section next time I take it off. I use Fluid Film to slow down corrosion on the aluminum parts.
2. The cap has a 1" FNPT port for connecting conduit. Makes installation a bit more difficult than it needs to be, and makes removal of the lower half of the cap impossible without cutting the conduit. A better connection, in my opinion, would be a hole just large enough to admit 1" MNPT threads. Sealing would be accomplished by a smooth surface on the bottom with a gasket between it and the male adapter. Securing would be done with a thin 1" NPT threaded locknut inside the cap. Pretty much how liquid-tight non-metallic conduit connects to an electrical box.
3. The gasket around the casing and the conduit openings is nitrile rubber from what I can tell. EPDM probably would have been a better choice, and a design that uses standard size O-rings would be an improvement. For venting, it has a #30 stainless steel mesh screen surrounded by what seems to be a neoprene gasket. The three gasket pieces seem to be adhered instead of bonded, and mine broke fairly easily at one of these joints. Cyanoacrylate adhesive can do a good repair job, but the manufacturer also quickly sent me a replacement without any charge or issues. I restored the NBR gaskets with methyl salicylate (this was after the break, so not the cause of it), and applied a thin layer of silicone grease to them and the neoprene gasket.
4. Doesn't matter for my current setup since I don't have a ground wire anyway, but a grounding screw seems like it would be a sensible inclusion, especially when used with plastic conduit and casing. Easy enough to add one though.
5. A bit nitpicky, but rather than the included stainless steel screws/nuts, just use aluminum screws and tap holes in the bottom part of the cap. Regardless, I use metal-free antiseize on these screws and the one clamping the casing.
6. Instead of a mesh-screened hole for venting, it wouldn't be too hard to expensive to have a pair of spring loaded vents - one for intake, one for exhaust. A very low cracking pressure would be best for most situations, but this could be adjusted by changing out the spring. You could even have a mechanism that would allow the cap to be fully sealed.
Here's a very rough model I threw together for an improved cap. Blue areas are sealing surfaces. Casing and conduit are obvious. Small holes are screw holes, the two remaining holes are for intake/exhaust. Could be machined very easily from a $10 piece of aluminum, and the remainder used to cast the top half. Only thing I'm not happy with is that the red section of the O-ring around the casing wouldn't be compressed by the top half. A small piece could be added to that area that would be pushed down by the top when it's screwed into place. Not sure if I'll have the time to make this anytime soon unfortunately.
Since I finally got my pump freed, I now have the opportunity to overthink things and fix them until they break.
This will be the first of three posts, since apparently everything at once is a bit over the character limit...
The Well
My well is in the coastal plain of Maryland, so I expect mostly sediments on the way down. I won't go into the full water composition, but notable are extremely high iron and manganese levels, and a pH of 5.6. The state apparently lost records from the period when the well was drilled, but they believe it was in 1962. The casing is 4" Schedule 40 PVC in 20' sections. Strangely, measuring the distance between joints has most of them at almost exactly 20', but the second and third sections down measure over 4" too short. Maybe they were damaged on the ends and cut before installation? The total depth is about 83.4 m (273.5 ft), although there may be a layer of sediment that stopped my measurement short.
Regarding the condition of the casing, I found that several sections are very... bumpy? There is also a damaged section at around 50 m (165 ft), right next to where the pump previously sat. That probably isn't coincidence, and I'm guessing the pump must have overheated at some point and weakened the PVC. I couldn't get a great view, but it almost appears cracked. The pump was stuck on this section, so I'll just reinstall right above it. I'm considering trying to get a length of 3.5" PVC pipe into the damaged section to reinforce it, but it's difficult to assess the situation under water with such high turbidity.
Here's a video trying to show the damage (on the left): https://streamable.com/4u5s9e
And here's a bumpy part of the casing compared to a normal one:
The static water level is around 39 m (128 ft). Drawdown levels will have to wait until I have the pump back in. I measured the water level with a camera at the end of a distance-marked fiberglass cable, but also tested echo distance measuring using my phone to emit a signal. A phone could also be used to record the signal and echo, but I used a microphone connected to my laptop so that I could skip transferring the recording, and probably get a higher quality recording. I used Audacity to measure the time between signal and echo.
Here's what three pulses and their echoes look like:
The pulse itself is very clearly defined, but the echo is a bit dispersed. I used the the first point where the echo became distinguishable from the noise background as reference. If we assume the timing can be measured to within a millisecond, that corresponds to a max distance measurement error of about 17 cm (6.7 in). Things like pressure and humidity can influence the speed of sound by a fraction of a percent, but more significant is temperature. An estimate is fine here though, since the change in air temperature from 10-25 °C (50-77 °F) is less than a 3% change in the speed of sound. The well's water temperature seems like a decent estimate for the air temperature. There are plenty of online charts and calculators that show the speed of sound for a given temperature.
Anyway, for my well, I estimated 342.3 m/s as the speed of sound. I measured the delay for five echoes to a precision of 0.5 ms and got 0.2295 s for all five, so repeatability is very good. One thing to note is that despite me setting the pulse frequency to 10 kHz, the highest amplitudes of the signals and echoes were well below 1 kHz. The timing was the same when isolating to these frequencies, so I don't think it matters much, but it might be an indication that 1 kHz would be a better choice than 10 kHz.
That works out to 342.3 m/s * 0.2295 s / 2 = 39.28 m (128.87 ft) measured acoustically, compared to the 39.09 m (128.25 ft) measured directly. Assuming my direct measurement is correct, and assuming the water level didn't change in the hours between these two measurements, that's less than a 0.5% error. Not too bad. If we assume my timing and my direct measurements were correct, that would mean an actual speed of sound of 340.7 m/s, which would relate to a temperature difference of just 2.8 °C (5 °F) from what I estimated for my measurement.
Making an app that does all of this at the press of a button wouldn't be too difficult, I'll probably give it a try when I have a little more free time. Just don't go dropping your phone down a well. I also plan to create an acoustic distance sensor to install ~120' down to give me continuous monitoring of levels over time, but I don't have time for that just yet either.
The Cap
My cap is from MAASS Midwest, model WTCC-4. I wanted something that was aluminum (or at least, not plastic/steel/cast iron), vented, and had a connection for electrical conduit. This fits all of those requirements, but execution could be a bit better. I'm happy overall with it though - it does its job and was fairly cheap.
Some thoughts for improvement:
1. The casting isn't as flat as I'd like to see for the mating surfaces, but honestly it's as good as it needs to be considering this is a vented cap. The opening for the casing is also much larger than it needs to be. It has a screw to tighten against the casing, but a tighter initial fit would have been nice (or having three screws for tightening to a more centered position.) I cleaned up the mating surface of the upper section to have a continuous flat path along the seals, and will do the same for the lower section next time I take it off. I use Fluid Film to slow down corrosion on the aluminum parts.
2. The cap has a 1" FNPT port for connecting conduit. Makes installation a bit more difficult than it needs to be, and makes removal of the lower half of the cap impossible without cutting the conduit. A better connection, in my opinion, would be a hole just large enough to admit 1" MNPT threads. Sealing would be accomplished by a smooth surface on the bottom with a gasket between it and the male adapter. Securing would be done with a thin 1" NPT threaded locknut inside the cap. Pretty much how liquid-tight non-metallic conduit connects to an electrical box.
3. The gasket around the casing and the conduit openings is nitrile rubber from what I can tell. EPDM probably would have been a better choice, and a design that uses standard size O-rings would be an improvement. For venting, it has a #30 stainless steel mesh screen surrounded by what seems to be a neoprene gasket. The three gasket pieces seem to be adhered instead of bonded, and mine broke fairly easily at one of these joints. Cyanoacrylate adhesive can do a good repair job, but the manufacturer also quickly sent me a replacement without any charge or issues. I restored the NBR gaskets with methyl salicylate (this was after the break, so not the cause of it), and applied a thin layer of silicone grease to them and the neoprene gasket.
4. Doesn't matter for my current setup since I don't have a ground wire anyway, but a grounding screw seems like it would be a sensible inclusion, especially when used with plastic conduit and casing. Easy enough to add one though.
5. A bit nitpicky, but rather than the included stainless steel screws/nuts, just use aluminum screws and tap holes in the bottom part of the cap. Regardless, I use metal-free antiseize on these screws and the one clamping the casing.
6. Instead of a mesh-screened hole for venting, it wouldn't be too hard to expensive to have a pair of spring loaded vents - one for intake, one for exhaust. A very low cracking pressure would be best for most situations, but this could be adjusted by changing out the spring. You could even have a mechanism that would allow the cap to be fully sealed.
Here's a very rough model I threw together for an improved cap. Blue areas are sealing surfaces. Casing and conduit are obvious. Small holes are screw holes, the two remaining holes are for intake/exhaust. Could be machined very easily from a $10 piece of aluminum, and the remainder used to cast the top half. Only thing I'm not happy with is that the red section of the O-ring around the casing wouldn't be compressed by the top half. A small piece could be added to that area that would be pushed down by the top when it's screwed into place. Not sure if I'll have the time to make this anytime soon unfortunately.
