Flameproof Switch

[ronhud]

I would like a flameproof switch (or something that provides switching without the risk of sparking) for my bio-diesel setup. Does anyone know if these can be bought relatively cheaply and if so where? As my processor is in a shed it isnt very handy to site the switches elsewhere. I have googled but all the listings seem to be heavy industry orientated.
Ron

[haydn callow]

would a spark ignite bio diesel ? or any of the componants that go into it ??

[g8dhe]

seem to be heavy industry orientated.Ron

There aren't any domestic requirements for such switches!!
Your best bet would be to have the switching remote from the location that is likely to have vapour present. Another method would be to use low voltage remote switching to a location where again you are vapour free. Otherwise yes your into industrial and mining type setups!!!

Do you really need it anyway ?

The cheapest solution would be something like a Firemans switch as fitted at petrol stations. But I don't think they are actually rated as vapor proof.

[rwill19050]

Use a solid state relay, takes very low voltage to operate it (3 volts will do it) and you can switch fairly high AC current with no sparking.

[ronhud]

The process involves methanol at one stage so itis better to have non sparking. I did think about solid state relays - dont know anything about them except a low level current opens or closed a high level current So rwill - is it possible to buy a ssr with a button or switch built in for the low level current - or do I have to start into putting components on a board?
Thanks
Ron

[rwill19050]

The process involves methanol at one stage so itis better to have non sparking. I did think about solid state relays - dont know anything about them except a low level current opens or closed a high level current So rwill - is it possible to buy a ssr with a button or switch built in for the low level current - or do I have to start into putting components on a board?
Thanks
Ron

Ron, I have PM'd you

Richard

[MountainGoat]

daveblueozzie's brother has been making his own bio diesel on the Isle of Lewis for quite some time. Perhaps Dave could find out what kind of switch his brother uses for you if he has the time.

[helen&tony]

Hi
What about a waterproof switch outside the shed? there's those switches with a flexible plastic / polythene cover over them that stand up to a good soaking.
Cheers
Helen

[g8dhe]

A major problem with SSR's are that they are NOT intrinsically fail safe. Most failure modes cause the device to start carrying current rather than to fail open circuit. Raised temperature causes the substrate to leak which inturn causes the device to turn on, significant pulses on the supply can also cause the device to turn on without warning.

What devices are powered in the Bio-Diesel setup ( and don't forget any lighting circuits as well) ?

[teenmal]

A major problem with SSR's are that they are NOT intrinsically fail safe. Most failure modes cause the device to start carrying current rather than to fail open circuit. Raised temperature causes the substrate to leak which inturn causes the device to turn on, significant pulses on the supply can also cause the device to turn on without warning.

What devices are powered in the Bio-Diesel setup ( and don't forget any lighting circuits as well) ?

Very good point about lighting,fit FLP light units to be safe,and SSR are not reliable as g8dhe stated.

[rwill19050]

A major problem with SSR's are that they are NOT intrinsically fail safe. Most failure modes cause the device to start carrying current rather than to fail open circuit. Raised temperature causes the substrate to leak which inturn causes the device to turn on, significant pulses on the supply can also cause the device to turn on without warning.

What devices are powered in the Bio-Diesel setup ( and don't forget any lighting circuits as well) ?

Very good point about lighting,fit FLP light units to be safe,and SSR are not reliable as g8dhe stated.

Can I ask where you got that very worrying information from.
I have use said devices for years in industry, no problems.
I think the manufactures would be very interested to hear of your problems regarding substrate leakage.
As for significant pulses, basic good practice when using any solid state switching, is to put filters (cap/inductor/vdr) across the inputs (well, it was when they trained me in electronics).
Texas Instruments, Crouzet, Crydom, Omron & Siemens are just a few manufactures / suppliers of SSR's, without any major published problems, so which are the one's you found unreliable?
Perhaps I have just been lucky, but I doubt that

[g8dhe]

rwill try these application notes http://www.ssousa.com/appnote050.asp note the practical experimental notes at the end.
or these http://machinedesign.com/BDE/Electrical ... e6_14.html this describes the failure modes quite well.
Then take a look at this chip - its designed to DETECT such failures and report them!!
Again another application note from another manufacturer, the first two para's prefacing the actual data sheet labled PRECAUTIONS you don't often see datasheets telling you to take precautions in use at the very top of the sheet, it discusses the two failure modes;
"..... Note that an SSR has a small leakage
current when the contacts are “open”. Normal failure condition is contacts
“closed”. A special Fast Blowing I2T fuse and a mechanical interrupt switch are
recommended in the load circuit. In certain applications a mechanical interrupt
switch should be installed in the control circuit."
They suggest as you notice from above a seperate mechanical isolation switch ....

[Grahame at work]

I'm no expert on hazarous explosive environments but get involved to some degree regards off shore oil / gas installations.

If you are concerned by the possibility of a spark from a switch then you should be concerned about the circuits that you are switching. In an explosive hazardous environment ALL equipment is designed to meet one of the following:

1) Limited voltage / current circuits that are not capable of generating a spark
2) Enclosed by explosive proof housing that is design (and certified) to contain any explosion that occurs inside
3) Enclosed by a housing (certified) that is purged by a higher than atmosphere air pressure such that explosive gases can not penertrate

I don't know anything about the process but as was pointed out other folk do this so I wonder if you realy have a requirement - if you did HSE and your insurance company may well want to know

regards Grahame

[mikeonb4c]

I visited Rons installation last week - very impressed. He has good ventilation in the shed - an important point. I think, for what its worth and as said by someone higher up this thread, that the simplest thing would be to have anything inside the shed hard wired, with the (waterproof?) switches outside the shed. Keeps it all low-tech low-cost and simple and should (as far as I can see) be very fit for purpose.

Incidentally, I came to appreciate, after being shown what was involved by Ron, the art of the biodiesel brewer and how it would not be for everyone. As Ron said, it makes sense if you have time on your hands, but not a job to be doing if distracted by other time pressures.

The other thing of course iis to be able to source sufficient waste oil. With Jamie Oliver tut-tutting us over fatty food, and bus companies prowling for cheap fuel and signing up restaurants to collection deals (or summat like that), finding the stuff may get tougher. On which score I'm sure Ron (hope I don't embarrass him here) would welcome any local sources happy to receive offers of collection from him.

Also interesting was Ron saying that in cold weather he found 100% biodiesel was too much. I found myself wondering if a little flashpoint raising / waxpoint lowering additive might help. I remember doing a little research on adding kerosene or white spirit some time back (and BF guru TGP accorded with it) and the findings suggested a solution might lie in that direction

[bigdaddycain]

daveblueozzie's brother has been making his own bio diesel on the Isle of Lewis for quite some time. Perhaps Dave could find out what kind of switch his brother uses for you if he has the time.

There is no switching involved there tony, it's pumped straight into the tank.