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 ?

  [ You are not allowed to view attachments ]  

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 
Second - check that the piezoelectric crystal works - done 
Thirdly - get a suitable small propane cylinder - Facebook Marketplace provides 
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 

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.

  [ You are not allowed to view attachments ]  

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

  [ You are not allowed to view attachments ]  

  [ You are not allowed to view attachments ]  

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 
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 

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….

[awemawson]

Wakes people up John !

I tried it this morning, and yes it can be set up turned on and in two minutes is banging away. Measuring with a sound meter I'm getting 115 dB five foot away at 90 degrees to the barrel, but it doesn't come across as anything like that on a video recorded by iPhone  .

[John Rudd]

Sounds effective enuff….how long will a bottle of gas last?

[awemawson]

They say 17,000 pops from a 20 lb propane tank but I'm not counting !

[John Rudd]

Gotta be cheaper than 12 bore carts….

[vtsteam]

Excellent, Andrew! 

Plus a fun device! 

[vtsteam]

Oh, just thought of this.... there are a lot of inexpensive adjustable propane regulators offered these days for gas forges and foundries both on Amazon and EBay. They often come with hoses, packaged with ready made forges, etc. Or can be purchased separately. I think the range of pressures they can be adjusted to would include 1.4 bar.

[awemawson]

Yes I spotted those on eBay for about £20 Steve but thanks for the heads up. Actually I have a feeling that I have one buried away somewhere - I think that I got it for a radiant heater that came my way.

A slight complication would be grafting on the needle / throttle valve but I'm sure that that would be achievable with a bit of tapping and threading.

Had a brief visit from someone who keeps a few sheep here - he was complaining of birds eating his 'sheep creep' (small diameter sheep rolls for young lambs) at another farm. So I gave him a demonstration - he was AMAZED at the bang. That video gives no sense of the loudness in real life 

[vtsteam]

I like the fact that it's an all-mechanical mechanism powered by the gas pressure. It's a refreshing change from the Digital Everything (D.E.) Man, my wife's new Honda just went completely dead, because one of its 16 modules went crazy. Nothing wrong mechanically with the car, but it turned itself on overnight and drained the battery down to 5 volts.

Mechanical stuff like your crow popper. How simple. Brought back to life with pieces of real material put back into it.

[awemawson]

Yes Steve, I like the uncomplicated things!

Latest version of this Zon Banger uses a 12 volt battery, has timers for time day, of week, periodicy, set back from dawn and goodness knows what else and loads of flashy lights.

No flat batteries with mine !

[vtsteam]

Exactly!