Gallery, Projects and General > Oooops!

Boom - or the Power of Compressed Air !

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My nice civilised Hydrovane 15 (well I think that it's a 15 but never found a model number on it!) was cutting in a 85 psi and out at 125 psi which has been fine until I got my CNC Plasma Table - the Hypertherm PM45 plasma cutter on it specifies it at 90 psi (although it regulates it lower internally).

So a job yesterday was to tweak the pressure switch on the compressor up just a tad so that it never falls below 90 psi. Often compressor pressure switches - or at least the better ones - have settings for maximum pressure and hysteresis or dead band, thus setting the range from 'cut in' to 'cut out. But not this one - it's a cheapy generic one with only the maximum pressure settable. No problem, increase it from the 125 psi upper limit to a bit nearer the 150 psi that the compressor is rated at. I checked the test pressure of the tank and there was loads of margin, so 'one flat at a time', I tweaked the adjusting nut and cycled the compressor noting where it switched off.

I got it up to about 140 psi when suddenly the Hydrovane would not raise the pressure one iota. I thought I'd done massive internal damage to it, so a bit miffed I left the Portakabin where the compressor is housed, to go in the main workshop to google for technical diagrams of the beast.

As I got to the door, a chap that I have at the moment lowering a massive Laurel hedge called over saying he was glad I was ok as he'd heard the 'loud explosion', and come knocking on the locked workshop door to check I was ok :bugeye:

What explosion - I'd heard nothing ! So I went hunting along the considerable length of my air distribution system and eventually found the culprit. There was a three way Tee joint, where one branch is for future expansion, and the blanking plug had decided it was no longer going to stay put  :bang:

Now this is a 'proper official blanking plug' for 25 mm MDPE pipe certified for pressures in excess of what I'm using, so maybe I'd not tightened it quite as much as I should have. The plug is a harder plastic than the pipe, and I suspect that the 'grippers' don't bite into it as much if at all.

So no wonder the poor old Hydrovane couldn't raise pressure  :lol:

However, the huge explosive blast sadly cleared the top of the cupboard where the joint is, knocking to the floor a Prom programmer and my Textronix cable measuring device. Falling onto a hard floor they both have suffered damage, and as they fell, they knocked the polycarbonate safety shields off my Fanuc Tapecut Model M wire EDM machine but luckily they survive the encounter.

I replaced the original blanking plug, (which had vanished!) with another from stock, and tightened it up murder tight, but today I found the original way over the other side of the barn. It must have bounced all over the place to get where it was   :bugeye:

If that had have happened to me, I think there would have been a few four letter words involved. :bugeye: I'm surprised you don't stock the cap ends for the 25mm pipe.  :wave:

Pete, I do, but that would have involved a stub end of pipe and two inserts, whereas the plug is just ..... a plug  :lol:


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