View Full Version : OT: Locating buried PVC water line

04-18-2018, 08:43 PM
I am helping a friend locate a non-leaking PVC water line. We are using a method that he learned from a water utility: place a fast acting valve on the line that creates a leak and reduces the pressure, then turn off the valve quickly and listen for the thump. I supplied an Asco solenoid valve and an on-off timer and he, being an electronic engineer began with a geophone and oscilloscope. We have had sorta moderate success with this but not enough to pin point the line to begin digging.

I decided to try the ear to the railroad track and put my ear to the ground. I can clearly hear the thump but again it is difficult to determine the amplitude. Scott said that he was reminded that the utility used an acoustic geophone that was a brass cylinder about 4" OD with a flat sheet metal cap and a tube soldered into it for a rubber tube to the operator's ear. This would be a diaphragm and like a stethoscope would amplify the sound. Does anyone know if the cylinder is open at the ground contact end or any other details such as thickness of the diaphragm that would help us reverse engineer this?

I found this on the web: https://www.farmshow.com/view_articles.php?a_id=467. The author used a piece of 2" PVC with a Styrofoam cup taped to one end and a stethoscope taped to the closed end of the cup. This implies that the acoustical geophone is open at the bottom. We are going to try the 2" PVC next but in the mean time I would like to figure out the pro type acoustical geophone.

Jon Heron
04-18-2018, 10:22 PM
How big is the pipe?
If you can fish a wire through the pipe a standard inductive locator will also work.
If that is not possible witching or divining is your only hope in my experience.
Failing that start digging.
Good luck!

04-18-2018, 10:26 PM
Also handy for moles!

Bob La Londe
04-18-2018, 11:02 PM
I've had mixed success running a metal fish tape down a pipe and using a cable locator. Obviously you have to open up the pipe to do it.

04-19-2018, 01:33 AM
Y shaped branch is the old school way.

04-19-2018, 02:40 AM
Y shaped branch is the old school way.

A wire cloth hanger is the latest "know-how". :)

04-19-2018, 02:44 AM

04-19-2018, 02:53 AM
Or you flush something radioactive and trace its progress with a radiation meter. Doctors do it to you, surely you can do it to locate a pipe. It would probably work, but I'm not advocating such a method. Surely there's a transmit-receive device made that would enable detection of anomalies in the structure of the ground. A large scale stud finder perhaps. Chances are though that it would take something quite wide to detect at a few feet or more of depth (where pipes might usually be).

I wonder if you could 'order up' an SAR image of the land where this pipe is. I wonder what is the state of the art in this type of imaging-

Richard P Wilson
04-19-2018, 03:03 AM
What sort of distance are you talking about? Is this from a utility company main to your friends property? PVC pipes, which aren't traceable with a CAT scanner, unlike metal pipes, should be laid with a warning tape incorporating metal strand for just this sort of situation.
At worst, you will just have to dig a series of trial holes to physically locate the thing. Once you have done the first one or two, and got the idea of the direction its heading in, it becomes easier. After all, the ground has been dug out once already to lay the pipe, so redigging won't be too difficult.

04-19-2018, 08:13 AM
How close are you hoping to get and what kind of soil? At a golf course I worked at we had a long, sharp(long tapered point) steel rod with a steel pipe handle welded on top to make a 'T'. Wet soil is a must. Just push it in and run a series of spots in a perpendicular line. We could easily hit a 2" pipe 18" deep. Obviously this wouldn't work in rocky soil. Trenching perpendicular to the direction it lays is what I have had to do once I get close.

04-19-2018, 08:35 AM
Can you maintain turbulent flow in the pipe for a test period?

If so, you might be able to detect it with a detector similar to an electret acoustic sensor I developed
for detecting water flow in firefighting some years ago.

Info for your electronics friend:
use a small 2-wire electret sensor down hole in a tube.
Quad op amp eg LM324 circuit on battery :
High gain audio amp
Precision rectifier
Low pass filter on the dc signal.
level indicator eg to his oscilloscope

This would not be very directionally sensitive but will be sensitive to proximity to the turbulent flow.

04-19-2018, 08:50 AM
Had the same issue several years ago trying to find a 3/4 inch plastic water line, had a friend come over and tried the divining rod trick with no luck. Ended up running a trencher across the area I was pretty sure where the line was, issue solved when I hit water. In my case I was going to tap into the line anyway, cutting it wasn't a big deal.

04-19-2018, 08:53 AM
Call diggers hotline?

04-19-2018, 09:15 AM
I have a disaster waiting to happen with underground plastic piping. Hundreds of feet divided into three branches with no shutoffs. A leak could start anywhere without a clue where it is. One day I asked a friend from the rural water company if he had put it in. He said no but if I had I would have trenched along this fence here to here to... Made perfect sense. First to an outdoor hydrant closest to the meter them branches to another, and the house and then the barn. One morning with thin snow blowing sideways and the sun just right I could see the forty year old trench clearly beside the fence. If I ever have a leak I am confident this 69 year old could pick up a spade and dig out the first hydrant and find the start of the branches, add valves and have some place to start.

old mart
04-19-2018, 01:14 PM
What about a water diviner?

04-19-2018, 04:03 PM
I would make a hot box. That would be a simple tank with an submersible element in it. I would tie in where you can ,most likely at the shut off valve. Then i would attach a hose as close to the end of the line as possible. A garden tap would do nicely. Then I would run a hose back to the box.

Then I would pump the hot water in the line and use a thermal camera to pick up where the heat differentiation is and that is where your pipe is.

04-19-2018, 04:09 PM
I do like the hot water solution, ir camera, sorted, clever, much safer than radiotracers!( we used lots at work, I remember a guy making the dose got it blown all over himself, we had to shave his hair off, bag it then bag the bag empty the sump of the decontamination shower into barrels and have the NRPB crawl all over us for a week, Eric did look funny without hair.

04-19-2018, 05:50 PM
Your electronics friend nearly had it. Just need two microphones fed to the oscilloscope and observe the phase difference.

04-19-2018, 10:19 PM
Well, this has been interesting. A little more detail seems to be in order. The 1" PVC pipe is on Scott's property so the utility is out. Soil is wet and rocky.

We could trench and cut the pipe but it would help to have a better idea where it is. The hot water method is interesting but the pipe is about 2' deep and it might take a lot of hot water to warm wet soil to the point where it could be detectable on the surface. We only have a Harbor Freight IR thermometer and that is probably not sufficiently sensitive.

Dowsing: I remember the days when John Campbell was editor of Astounding Science Fiction and ran an editorial on dowsing. That's been around for a long time. Some swear by it and others swear at it. I have never had any luck. Tried it several times on a known run of water pipe. Guess I'm not an adept.

The ST20 Listening stick is exactly what I am looking for - essentially a stethoscope and a refined version of Hines pipe, cup and stethoscope.

The electret and op-amp amplifier is an electronic version of the listening stick. Either of us could build that. And Baz, could you give me a bit more detail on interpreting the phase difference. I know that the brass cylinder acoustic geophones are used in pairs and the volume difference between the ears indicates which way to move the geophones. How do we interpret the phase difference. We could use two electret microphones. BTW, are they more sensitive than the geophones?

Anyway, our thumper broke a section of 60 year old galvy and we are out of service until that is fixed. That gives us some time to work on the detectors. I have all of the material for the Hines detector on hand and will begin with that.

Thanks for the suggestions. I'll report back when the project is done and tell you what worked.

04-19-2018, 10:51 PM
Pipe is 2 feet deep, dig a trench 18 inches deep at a right angle in the suspected location. Then listen or probe for the pipe.

04-20-2018, 04:30 AM
Maybe we're going about this backwards- why not fasten a listening device to the closest part of the pipe that is accessible. Then listen to that while you thump the ground with a simple stick. Or you pump Jimi Hendrix into an actuator attached to the pipe and walk around the yard listening for Wind Cries Mary.

michigan doug
04-20-2018, 10:46 AM
Digging the 18" trench and -then- using a cheap I/R thermometer could work.

Trench until you create a gusher, crude but effective.

I also like the direction finding/2 microphone idea.

I am once again impressed at the breadth and depth of the community IQ.

04-20-2018, 02:08 PM
Me too, and their willingness to take the time to help.

04-20-2018, 02:24 PM
What about a water diviner?

Y shaped branch is the old school way.


04-20-2018, 03:10 PM
I only see a black rectangle in post #24
Inspection shows this: <iframe width="640" height="390" title="YouTube video player" class="restrain" id="yui-gen89" src="//www.youtube.com/embed/_VAasVXtCOI?wmode=opaque" frameBorder="0"></iframe>

04-20-2018, 03:34 PM
Couple of silicon bronze rods, l shaped, 14 x 7 seems to work, for some! I’m not going to say more as it only seems to work for some, an open mind works.
It’s certainly interesting

04-20-2018, 04:08 PM
The missing youtube link above is...


A belief in dowsing is caused by the ideomotor phenomenon. https://en.wikipedia.org/wiki/Ideomotor_phenomenon

And I myself have felt the effects of dowsing even when fully aware it was a purely psychological phenomenon. I held two metal dowsing rods and walked over where I knew an iron pipe was buried and sure enough the rods deflected as if by magic, exactly where I knew the pipe was. I was not consciously deflecting the rods at all. It was my own involuntary actions that caused the rods to deflect. If that same experiment had been conducted in a controlled environment (as shown in the Dawkins video referenced) where I did not know where the pipe was, there would be no correlative performance beyond the odds associated with chance detections.

Edit: Here's another example, including where Alan Alda demonstrates the ideomotor effect when he handles a pendulum...


04-21-2018, 06:48 AM
Also handy for moles!

Good idea but I'd get a stethescope for engines at horror fright & weld, braze a small dia gas welding rod sharpened where I could stick it into the ground then turn the water on & keep probing until I found it.

Joe Rogers
04-21-2018, 09:04 AM
Had a ruptured water main in the service road in front of our house. While it was running the inspector took out a stethescope with two tubes that had heavy weighted diaphragm mics attached. One source for each ear. switched them independently around the street and listened to the amplitude of the noise. In 5 minutes he had xed the street and shut off the water. He hit the spot of the leak in the pipe within a foot when the main was 10 feet down in the hole. Two sources and careful volume monitoring can do it cheaply.

04-21-2018, 02:13 PM
Joe are you describing a microphone with an electrical output or was its output a tube leading to an earpiece? You describe is as a stethoscope and that suggests to me the latter possibility. What Scott saw was a two brass cylinders with flat caps with a short small metal tube attached in the middle. Flexible tubing ran from that small tube to earpieces. There did not appear to be any diaphragm involved. The ratio of the area of the cylinder to the ID of the tube would be the amplification. I am going to work on that idea while Scott digs out the broken galvy and puts the system back in service.\

04-21-2018, 10:21 PM
I believe he is describing a Pollard Geophone Leak Detector.



04-22-2018, 06:42 AM
I believe he is describing a Pollard Geophone Leak Detector.



Being a plumber I could use this. How difficult would it be to make. Is there some kind of diaphram in those brass cylinders.

Joe Rogers
04-22-2018, 07:39 AM
I believe he is describing a Pollard Geophone Leak Detector.




That’s it exactly. Didn’t see the box though. Probably repurposed as a lunch box some years earlier...

04-22-2018, 07:14 PM
Pollard: that is it, exactly. So the question: is there a diaphragm inside the cylinders or are they hollow? I there is a diaphragm, where would it be. I'm thinking there may not be one.

04-22-2018, 07:27 PM
There are some photos of a Pollard Geophone in the link below that may give you an idea of the scale of the pickups and such. What is shown here suggests that the bottom of the sensors is closed, perhaps with a thin diaphragm.

Like here:



Also found this site that specifically mentions a "phosphor bronze diaphragm" in the description:


04-22-2018, 09:16 PM
Looks like a machinist's project. :)


04-23-2018, 08:14 AM
a geophone is a microphone for direct contact with the soil. it hears horse hoofs, engines, tires. invented by a Russian prince. we used these by the dozen on my last job:


I want to take one to Taos, find the alleged hum, see what shows up