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A Water Thumper: Finding buried plastic water pipes

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Pete W.:
Hi there, Andrew,

The following might be considered 'off topic' but it isn't really - it's evidence of the effectiveness of using water-borne pressure waves to detect sub-terranean goings-on:

First, a recap. for younger readers:  way back in the early days of U.K. wireless broadcasting, home radio receivers using thermionic valves (a.k.a. 'tubes') had a high tension ('H.T.') 'dry' battery for the anode circuitry and a low tension ('L.T.') battery to power the filaments of the valves.  Strictly speaking, the L.T. supply was a cell rather than a 'battery', it was a 2 Volt lead-acid accumulator in a glass jar with a carrying handle.  This, being a secondary cell, needed recharging at regular intervals.  The charging was usually performed by the local bicycle shop at a moderate cost.

Though this recharging cost was moderate, some householders begrudged it.  There was, on the market, a low voltage dynamo driven by a Pelton wheel turbine, arranged to be connected to the kitchen cold water tap.  This transferred the effort of recharging the battery from the householder's pocket to the Water Company whose pumps would now be the source of the required energy!

The Water Companies weren't at all enthusiastic about this particular piece of technology.  However, it was found that the alternating passage of the Pelton 'spoons' and the intervening gaps past the jet of the turbine launched an audio frequency pressure wave back up the water main.  This signal was very detectable by use of a metal rod placed one end on the bone behind the Inspector's ear and the other end placed on some accessible bit of the water main.  This enabled the Water Companies' inspectors to rapidly 'home in' on the houses where these dynamos were in use.  This sounding rod was/is a standard tool of the Water Companies' inspectors for leak detection.

Your intended set-up, Andrew, seems to be a modern version of the inspectors' sounding rod.

As recently as the 1960s, I remember an occasion when I was working at home (not because of Covid!) when my attention was drawn to a group of men in navy blue raincoats in the road outside my house, each of them carrying a sounding rod and taking turns to try it on the stop-cock beneath the pavement.  This was a group of trainees doing their outdoor practical under the tuition of their instructor.  So, it works.

Andrew, I wish you 'good hunting'.

Well, in the time that I was typing my post ......   :)   :)   :)   :)   :)   :) 

That's an amusing tale Pete - I'll give you another!

Back in that era some people were using the voltage difference between actual earth and the neutral line via a rectifier to charge their accumulators. This had started back in the DC distribution days when of course the rectifier wasn't needed, but the supply companies had the habit of sometimes reversing the polarity  to dissuade people from the practice by destroying their cells! 

Come AC distribution people soon found that if they were sufficiently far from the neutral / earth link (so perhaps at the far end of a street) there was enough voltage difference to get those lead acid cells charged!
(but you did need the rectifier)

Andrew I think that's a really clever idea using the thumper you made to trace the line. Very cool!

Sorry you got stuck, and VERY sorry you have contracted Covid!! I hope you will come through this with just the head cold symptoms. I guess it's inevitable that we will mostly all get it eventually. Our family has managed to avoid it so far, but I can't imagine that will continue forever, as we all get closer every day to resuming normal activity and increased exposure. There's just the hope that the variants have become less virulent and vaccinations may help reduce severity. Anyway, keep your chin up, and please get better soon.  :beer: :beer: :beer:

I do want to hear you trace that water line to the point you need  :dremel:

Thanks for the kind words Steve, much appreciated.

Well I’ve woken up this morning to think “what is all the fuss about?” No headache, very minimal sore throat, and as yet no sneezing unlike yesterday! Mind you I’ll probably get my ‘come upance’ later as it develops. So although we’ve put the quarantine flag up and are avoiding folk, I’m going to carry on as far as possible ‘normally’ which today means under the thumb and continuing fixing her poly tunnel !
Bad luck with the Covid, Andrew, but almost inevitable now.
I'll add that a positioning a long screwdriver against your ear and prodding various spots on engine is also a time-honoured way of detecting nasty goings-on inside.


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