The Craftmans Shop > New from Old
Reviving a Zon Mark 2 Crow Scarer / Propane Cannon
awemawson:
We have a crow problem - they eat more chicken feed than the chicken do and it has to stop !
Over the years we've tried various remedies:
Fake Owls that nod and turn their heads - OK for a while but the keep getting blown over by the wind
Friend with a 12 Bore shot gun - OK for a while but the effect wears off
Slow Match rope of bangers designed for the job - highly effective but once lit they keep burning for several hours.
Now not wanting to overly disturb our holiday cottage guests I wanted something that I could start and stop at will (ie when they are out for the day). As I don't want a shot gun on the farm I investigated propane fired crow scaring cannons. They seemed ideal apart from the price - over £400 for a set up.
So an eBay - "Spares or Repairs" one for £50 seemed a far better candidate - surely they can't be too complicated can they ?
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Well it duly arrived - time to start poking around
awemawson:
These work by squirting a charge of propane into the barrel and igniting it with a piezoelectric crystal that generates a spark.
First - clear the packed spiders webs from the barrel - done :thumbup:
Second - check that the piezoelectric crystal works - done :thumbup:
Thirdly - get a suitable small propane cylinder - Facebook Marketplace provides :thumbup:
Fourthly - connect up and try it - failure, internal mechanism doesn't cycle despite gas coming from the regulator.
OK - get it on the bench, rig up a compressed air supply at the required 1.4 Bar pressure and try it again - obviously it's not going to go bang as only on air. Yes it cycles the mechanism but leaks are apparent round the diaphragm.
The diaphragm is key to the whole operation - gas enters a chamber whose lid is rubber this bows upwards under pressure and latches a spring loaded device that releases the propane charge into the barrel then clouts the piezoelectric device making it go pop.
awemawson:
So soapy water tells me that the leaks are where the diaphragm meets the chassis - just squashed by four bolts clamping the chamber upwards.
Dismantling proved a tad tricky and unfortunately resulted in me breaking the gas chamber exhaust port brass fitting - but that's why we have lathes - make another - done :thumbup:
Close examination of the rubber showed that as well as the leak round the circumference there was a split in the middle that oddly didn't go all the way through.
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Rubber was 2 mm thick so I ordered some up which took ages to arrive and was actually 2.2 mm - never mind - press on and see if it works.
Well it did on compressed air on the bench but NOT on propane - more investigation required. It turns out that the genuine Zon pressure regulator that is supposed to output 1.4 bar was only putting out 0.5 bar - no wonder it's not working
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Now the pressure gauge has a bespoke needle vale attached to give a very throttled output as this regulates how frequently it goes bang.
Opening up the regulator I found it full of water :bang:
Cleaning it all up and reassembling it now will only give 0.75 bar at max adjustment - adjustment is supposed to be sealed but we are Engineers aren't we - it's only a screw!
Lots of fiddling and multiple dis-asembly and reassembly later I got it up to just over 1 bar but only by the expedient of packing the main spring with a big fat washer !
Does it work - yes by heck it does :clap:
Somewhat louder than a twelve bore shot gun, as set it cycles every two minutes with the needle valve as open as it will go. First 'shot' purges air from the pipes but after that off it pops nice and regularly
Joules:
Makes it easier shooting crows further down the line as none of them can hear the gun fire..
I can see a crow scaring cannon being effective, seeing one of their own whizz past on fire at near Mach 1
John Rudd:
Certainly an interesting- entertaining solution to a problem Andrew…. :clap:
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