Coffee Bomb

[FinerGrind]

I saw a picture of this on Jim7's twitter but didn't see a close up until I went to the link. I don't think I've ever seen a boiler blown apart like this!

http://www.thesun.co.uk/sol/homepage/news/3138214/Coffee-machine-blast-hurts-six.html

[Tex]

Two catastrophic failures; 1) Hi-limit tstat didn't work, 2) Pop off valve didn't work. I wonder who did the work on that puppy to screw things up so badly?

STUPID, STUPID, STUPID!

[John F]

I wonder who did the work on that puppy to screw things up so badly?

Every few years a maint man finds a pressure relief valve leaking on a big water heater in a school. Ironically it sometimes happens on a Friday and he caps it off to stop the leak and plans on ordering parts on Monday.

The explosion normally happens on Sun when not many people are there. 

[Tex]

I wonder who did the work on that puppy to screw things up so badly?

Every few years a maint man finds a pressure relief valve leaking on a big water heater in a school. Ironically it sometimes happens on a Friday and he caps it off to stop the leak and plans on ordering parts on Monday.

The explosion normally happens on Sun when not many people are there.  

You see it all the time: someone's working on an espresso machine and doesn't have the part needed at hand. The machine gets reassembled without the part or the part's deactivated. The part is forgotten because the machine works, and the machine is never made right.

I've also seen many instances of the hi-limit tstat bypassed, which can cause catastrophic failures like this. And guess what? It's usually the most experienced machine techs who do these stupid things. It's not because they've malicious intent or have suddenly gotten stupid; it's because of the backlog of work they have to do.

[milowebailey]

Looks like in the photo the pop off valve is still intact.... could a horribly scaled machine have a pop off valve so corroded that it doesn't work?

[Tex]

Looks like in the photo the pop off valve is still intact.... could a horribly scaled machine have a pop off valve so corroded that it doesn't work?

I saw that and figured it was the anti-vacuum valve. The pop-off isn't usually located in a drip cup (the anti-vacuum valve is); it's purpose is the release steam to prevent a catastrophic breach, so it doesn't need to be in a drip cup.

I've never seen a pop-off that was frozen with calcium, but I've seen pop-off valves with the safety wire removed so it could be screwed down tighter.

[yorel23]

So what is the best way to check that our safety pop off valves are setup and functioning correctly?

[crholliday]

So what is the best way to check that our safety pop off valves are setup and functioning correctly?

After seeing that picture, I would say just buy some spares (they are pretty cheap) and change every 2 years. I wonder what actually happened there. You need several failures for a tank explosion.

[Tex]

So what is the best way to check that our safety pop off valves are setup and functioning correctly?

Best thing you can do is make sure it's never needed. I use a 130°C hi-limit tstat on my machines, plus a solid state relay hooked up to the PID alarm circuit, wired in series (I'm a belt & suspenders sort). I check them by running the preset on the PID up to test the tstat & alarm circuit.

edited: I guess I should run it up high enough to check the pop-off too? I think I'll add that to my check list.

BTW: The pop-off is set at 1.8 bar.

[John F]

could a horribly scaled machine have a pop off valve so corroded that it doesn't work?

A slight drip/leak could stick it shut over time even if the machine is descaled.