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A Water Thumper: Finding buried plastic water pipes

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awemawson:
The Problem: I have a ditch and a stream, both of which are crossed by a 25 mm MDPE blue mains pressure water pipe - I'm ditching both water ways and need to avoid the pipes. Both were laid over ten years ago by trenching up to the the banks, and indeed down the banks as far as possible, then the pipe were trodden into the silt as deep as we could. Location known approximately but not accurately.

The Solution: A "Water Thumper" my google research tells me. This is a device connected to the nearest tap, and consists of a water solenoid valve and some electronics to rhythmically turn it on and off like a heart beat. This imposes a pressure wave ( and hence sound) in the pipe which can be detected by a suitable probe pushed into the earth.

. . . . how hard can it be to make that ?

So I ordered some bits off ebay. A pulsing bit of electronics, a water valve, a Chinese 'spy' listen through walls audio detector device  and a waterproof box.

I turned up a socket for the audio device and welded it to a suitable ground spike

awemawson:
The water valve persistently didn't arrive  :( Never mind I had a nice solid brass one intended for a different project - at least test it on the bench with that.



awemawson:
Now the circuit is pretty simple accepting that some one else has kindly programmed the PIC controller. There are two timers controlled by twiddle pots. One for on time and one for off.

I feed the circuit via a diode to save it from reverse polarity issues, and the back emf from the solenoid valve is quenched by another diode. All standard practice.

awemawson:
So outside for 'field trials' - literally in this case!

Setting up the device in the lambing field water tap (seven so far but one failed to prosper) sure enough I could follow it's feed pipe easily for the first ten foot or so but then things got complicated  :scratch:

The original trench I'd put in with my trenching machine ( bought wrecked off eBay and renovated for the project) to a nominal 18" but only 12" in places. However in the same trench was a length of 10 mm csa SWA armoured cable and I  think that this was also picking up the thumping and leading me astray.

The pipe went parallel to the ditch then turned 90 degrees across it and it was really this turning point that was vital to find. In practice the sound carried on in a straight line presumably carried by the cable. Finding the turn off point proved extremely difficult.

Now there were only certain points where it could cross the ditch as there is an intervening hedge of hideous Leylandii and it HAD to go between them. So I started on the other side of the ditch and picked up a very faint signal that I duly marked with a spray marker.

awemawson:
So how to proceed?

Well I decided that things were still too vague to steam on with the big  8 ton machine, I'd do some tentative scraping with the 3 tonner with a good 'banksman' looking for exposed blue pipe.

We did a really good clean up where the signal was - NO PIPE - we went 6 foot either side - STILL NO PIPE  :scratch:

BUT no water fountains either so perhaps a 'good thing'

Now the 3 tonner hasn't the reach of the 3CX with it's extender-hoe so the spoil got dumped in what would be the wrong place when I recommenced ditching with the big machine. OK put the little one away, get the 3CX out and shift the spoil from the mornings work.

This is where things got VERY messy and the reason is dead obvious when I think about it - hind sight is a marvellous thing.

 . . . . I got the big 8 ton 3CX STUCK FAST - 4 wheel drive, wheels spinning - stuck. It's not entirely obvious from the cab that the wheels are spinning, I thought at first I had some disastrous transmission fault!

 Eventually I had  to 'walk it out' using the back hoe as a pusher but it didn't go easily.

. . . . so WHY did it happen ? Well the field was already pretty soft from rain over the last few days but it was workable. However of course I'd been scooping copious amounts of extremely slippery silt from the ditch, and water from this was migrating to where I was with the 'zero traction' result that I've described.

At this point I gave up, put my toys away and retired for a cup of coffee.

It didn't help that this morning I tested positive for Covid  :bang: But in all honesty so far it just feels like a cold in the head.

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