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John McKee

Pressure Release Valves for Stills

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Our Kothe doesn't have a PRV on the still boiler, just on the jacket. However, it is heated by a water bath / bain-marie and the pressure release kicks on if .5 bar (~7 psi) is reached in the jacket. If the column somehow clogged, the pressure would build in the water bath first and ultimately blow out all the heat transfer medium (water) before much pressure could build in the still body. I think...

Really???? You might want to check out that theory......

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I don't pretend to know the finer details of Standards for pressure vessels but I do understand the basic principals.

If a certified pressure vessel had a 60 psi relief valve on it I would be reasonably confident in saying that the vessel itself had been tested to at least 90 psi

agporte, am I in the ballpark here?

If I was buying some type of steam boiler and it had a 60 psi safety valve on it then I would initially assume that it was designed and manufactured to not rupture till well over 60 psi. (a pot still is a steam boiler)

It was mentioned on page 1 of this thread that a pressure safety device needs to release VOLUME as well as pressure.

eg a 5 psi 3/8 inch valve is totally useless if the still tries to puke solids through that.

I'll need to check the code books tomorrow at work, but I know ASME Section VIII Pressure vessels can have relief valves set at the design pressure of the vessel. They are then allowed to have 10% over-pressure (21% for an external fire case) due to pressure drop across the orifice of the relief valve. For non-pressure vessels (below 15 psi) built to some other code, the set pressure needs to be adjusted to account for the pressure drop across the orifice so that the pressure inside never exceeds the design pressure.

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Our Kothe doesn't have a PRV on the still boiler, just on the jacket. However, it is heated by a water bath / bain-marie and the pressure release kicks on if .5 bar (~7 psi) is reached in the jacket. If the column somehow clogged, the pressure would build in the water bath first and ultimately blow out all the heat transfer medium (water) before much pressure could build in the still body. I think...

I like that little "I think..." added to the end of your post indicating your not confident with your own argument. :) A relief valve on the heat input side of the still (water bath/bain-marie in your case, steam jacket for many of us) will not activate if there is excess pressure build up on the vapor side of the still. They are separate systems that run at separate pressures and both have the potential to build up excess pressure if something goes wrong.

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I love that I somehow managed to kick off the first word of this thread! Aside from my name, you know what else this thread could use? More examples of PRV's (links to where to buy) that folks should consider implementing on the vapor side of their stills, if not already in place.

I get why a potstill with no weird packing that only runs low-wines would not necessarily need to be fitted with a prv, but... some additional recommendations of lower priced yet functional options (such as the apollo option above) would be great! Has anyone identified a viable sub-$50 tri-clamp option?

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I completely agree so I will share our experience. When we initially bought our equipment there were no PRVs. We installed a combo of the following:

http://www.supplyhouse.com/Burnham-81660530-Safety-Relief-Valve-15-PSI-for-All-Res-Steam-Boilers

http://www.ebay.com/itm/281174886992

$22 per still is a pretty cheap investment so we decided to install after hearing about the most recent accident. It's not the prettiest thing in the world but if it can save a life I'll live with it!

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In the idea of keeping it sanitary and or tri clamp. I have seen 2" (increased volume) caps with rupture disks very cheap. You buy the disk that ruptures at the pressure you desire.

Even ebay, has them a low as $8 for a SS316 2" x 5 PSI version, $19 for a 3" x 5 PSI version. Looks that you can have them from 1" to 4" that fit atop any tri clamp.

post-8489-0-35541900-1443555619.jpgpost-8489-0-93886600-1443555618.jpg

Looks to be more "professional than a brass water heater valve hanging on a $XX still.

I know low pressure house boilers were set with aluminum foil as a rupture disk. I have also seen water temp booster that had a teflon disk in a fixture similar to a tri clamp.

Or let's go low tech...a big natural cork, stopper...at least it would get your attention when it hit the ceiling.

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4 inch rupture discs at 6 psi (and cheap)

Much much much safer than a 3/4 inch spring loaded water heater valve

Well done Falling Rock.

Just make sure they are mounted so they cannot burn someone if they vent.

I really like the idea of the cork :unsure: , but there is a good chance that the cork could bind to the hole after a time.

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So glad to see this progressing from basically bullying by one party to others providing multiple avenues of approach in adding a safety device.

I like the idea of a sanitary rupture disc as it provides a nearly fail proof option (as well as easy to add to a triclamp port). Is there any downside to using one?

Thanks!

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I like the rupture disk things and it seems this is what I am seeing these days on most new brewery fermenters. The downside is that most of these tri-clamp PRVs have been designed for brewing applications where the contents of an over pressurized tank are not inherently dangerous.

The big advantage of the brass steam relief valves (designed for something that is potentially dangerous when released) is the ability to add a section of piping on the outlet to direct where the output goes if it does blow. Depending on the placement of the PVR this may or may not be a concern.

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Well, they're fragile, one-shot devices so keep plenty of spares around.

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Hey all,

I've used Rupture disks in the past in biodiesel applications...I think the last refinery I designed and built had something like 70 or 80 of them, all different ratings for vacuum, pressure and temp.

Overall, they're a great solution and I would be comfortable recommending them, but they have some of the same issues with regard to sizing and directing the discharge. The discharge piping for a rupture disk system has some specific guidelines as to sizing, flow, temperature allowed, and where it discharges. If you allow for a rupture disk system, the discharge piping should be at the very least welded pipe, directed outside of the building. (This avoids some of the issues mentioned above)

....and one notable foible...when they rupture, they're done. The difference to the PRV, is once the pressure has subsided to the crack pressure, the PRV should reseal.....meaning that you have a sealed vessel and you aren't venting gases from the vessel. With a rupture disk system, once the disk is blown, you're continually venting, until the entire contents of the pressure build-up have exhausted and the continued energy of the system (boiling, etc) has continued to vent until there isn't anything left to boil off.

Overall, rupture disks are a pretty expensive alternative to PRVs, but do have their place.

Cheers.

McKee

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I get that they are one time use, but if I did have one rupture it would indicate a serious problem with the still likely requiring a complete teardown.

Granted, like a K-type hydrometer it would always be a good idea to have a spare in case of accidental damage.

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Scanned through the rupture discs, the most interesting are the SaniTRX versions, since they are built into what looks like a triclamp gasket, meaning it can be placed in a standard triclamp joint for the pipe size, no fancy housings.

I buy a lot of surplus, but unless the thing is boxed and sealed, I'd be wary. There are guys asking $100+ for rupture disks that look like they've been unwrapped, in the bottom of a junk drawer for 3 years.

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My bringing up rupture disks was that they are cheap. There are lots of cheap rupture disks that fit a standard triclamp...very cheap. Then use pipe to get to floor.

Now, look at common materials you can make your own. We used to use aluminum or copper foil...there are charts that tell you the rupture values for the thickness...makes it almost free. Sandwich a piece of copper foil in between two tri clamp gaskets and done.

Remember, they're not supposed to be under pressure daily...just in case of an event!

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Guest James

Floor? Surely you mean safe exterior location with a flame arrestor..

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Boiler, steam jacket...you vent it where you need to.

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We use a 15psi relief valve, one on the jacket and one on the exit water for the deflag.

and nothing on the hot hazardous flammable vapor you are making??

EDIT; can anyone foresee a situation where a relief valve would be useful on the deflag. exit water??

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and nothing on the hot hazardous flammable vapor you are making??

EDIT; can anyone foresee a situation where a relief valve would be useful on the deflag. exit water??

You definitely need one on the defleg for thermal expansion and vaporization of the exit water if there is a possibility for the water to be blocked in (with a valve). Say you accidentally close an isolation valve and run alcohol vapor through the defleg. The vapor will heat the cooling water and thermally expand (probably not vaporize), so a very small relief valve is needed.

I'm also working on a simple formula everyone can use for a sizing relief valve on the still. When I get enough time I can type up how to calculate.

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Pete,

Nothing on the condenser, no need its open to the parrot. If there is a reason that you might think i need one im all ears. I just dont see why since the whole column would need to clog.

See above for the deflag, i use valves for water adjustments and if one gets shut off it allows the vapor to escape.

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We only run a valve on the dephleg water inlet, the outlet is completely open to atmosphere. Any reason others do it differently?

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You definitely need one on the defleg for thermal expansion and vaporization of the exit water if there is a possibility for the water to be blocked in (with a valve). Say you accidentally close an isolation valve and run alcohol vapor through the defleg. The vapor will heat the cooling water and thermally expand (probably not vaporize), so a very small relief valve is needed.

I'm also working on a simple formula everyone can use for a sizing relief valve on the still. When I get enough time I can type up how to calculate.

I will be interested in seeing what you come up with as a calculator.

Although if you look hard enough I am sure regulations already exist. Stills may not be specifically listed but vessels with boiling liquids that produce hazardous / flammable vapors must have specific sized safety valves. I don't know where to find the regulations but I am confident they do exist.

Your comment about a relief valve on a deflag is in my opinion totally over the top. With a stop valve on the outlet, the expanding water will push back up the pipe where it came from. Even if for some strange reason someone put a stop valve on inlet and outlet of the deflag there is still no danger. The water in the deflag won't get anywhere near boiling point. The thermal expansion of the water will not rupture the pipe. Normal domestic small diameter pipes will take hundreds of PSI. Definitely not recommended but I have seen domestic water pipes used for hydraulics at 3,000 PSI

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