Home-made, high-volume Pressure Cooker

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Puma
surfing when I can

Registered: 10/08/09
Posts: 319
Loc: BC
Last seen: 2 years, 9 months

Home-made, high-volume Pressure Cooker

3
#11304231 - 10/23/09 02:37 AM (16 years, 10 months ago)

Hey shroomers!

My neighbor and I just built a kickass pressure cooker. I'm totally stoked. She's a monster. Here she is during testing:

Sadly, my camera ran out of batteries just before we painted it black. Paint dries faster on a warm surface, so we painted the PC as it was cooling from its test run. It looks slick with the new paintjob, so I will post new photos soon.

Okay... the basic stats:

Using my rough measurements of 14x40 inches, using the formula for the volume of a cylinder, this thing holds about 110 quarts, over 100 litres. That's a lot of filter patch bags to knock up with LC!

That's also about double what the largest All American PC holds.

NOTE: you need to scrub the inside of any propane tank!!! It stinks like old rotten cheese in there.

This monster PC cost me under 200$, which includes all materials (mostly from the scrap metal yard -- an amazing resource for many areas of mycology) and a wage of $20/hr to my friend who has a machine shop in his backyard. To keep costs down, I was there to do the grunt work, like grinding down bolts and painting, as well as making decisions about extra safety features (I wanted them all).

The machine shop was in a trailer next to his house, powered by 220 volt cord buried in his yard.

Here's the shop:

Okay, so let's back up a little. I'm a noob. I once grew shrooms in high school; I've been busy ever since, and now, in my early 30's, I'm getting back to it.

Wanting to get back into shroom-growing, I had to make a decision: invite contamination by trying the many dubious "teks" that claim to avoid using a PC, or, find a way to acquire one.

I want to grow bulk, and wanted a PC that could handle volume. The largest AA PC only handles about 50 qts.

Over an evening of moonshine with my friend, we decided to go for double that volume: 100 or bust.

I want to acknowledge a previously successful build of a PC using a beer keg, as detailed here:
[url=keg tek]https://www.shroomery.org/forums/showflat.php/Number/10891050/page/9[/url].

Although that tek worked, a beer keg is only required to handle the lower pressure that it takes to contain C02. Beer kegs are thinner than a propane tank, and thus, much more dangerous. Propane tanks are not only larger, but built of thicker steel, to handle hundreds of PSI.

We started with a tank that looked like this:

(with the nozzle removed, and the rim set in place but not yet welded).

Taken a few days later, here's a pic of the top, with the rim welded in place, an O-ring groove lathed into the rim, a matching O-ring set into the groove, and finally, a metal plate -- the lid -- lathed into a nice circle, and drilled with eight 5/16" holes, to match the threaded holes sunken into the rim (got all that?!).

Note: I had to grind down the bolts and round off the ends on a grinder, so that they bit enough thread to apply pressure to the O-ring (and thus seal the PC).

SAFETY FIRST:

I don't want to blow a hole in my roof when I start using this beast at home. So, in addition to the pressure gauge (taken second-hand from the lid of a wrecked All American PC I found in the local scrap-metal yard aluminum bin), I wanted two things: (1) an automatic, adjustable pressure-release valve, and (2) a manual pressure-release valve.

The manual valve (left, above) was easy. It cost $15 at a local automotive hardware store ("Okay! I'll go. On my motorbike, through the rain. Be back in 10 minutes."). We used a tapered pipe fitter's tap to sink the threaded hole, wrapped Teflon tape around the threads of the valve, and sunk it into the lid. Essentially, I flick a switch, and it starts bleeding pressure.

On the right is the beauty that we machined ourselves. It is a valve that is triggered by pressure. The "seal" -- which is never a complete seal, but allows pressure to dribble out, or gush out, depending on A) the pressure, and B) the valve setting -- is an inverted cone of metal resting in a hole. The cone can be lifted by pressure in the tank, to release pressure. By stacking washers as weights, or removing them, I can adjust the pressure it takes to release steam. On the test run, I determined that by stacking 2 washers on the valve lid post, I could maintain about 17 PSI with the propane burner turned way down.

Empty, with 4 litres of water, it took less than 15 minutes to reach 15 PSI. It'll take more heat to raise pressure with a full load of substrate bags, of course. But we were previously considering insulating the tank, and now I know that this is unnecessary. It absorbs heat like a mofo!

The adjustable pressure release valve is simple, but takes a skilled machinist to make. In my town, a mainstream metal shop charges $80/hr and won't let you hang out next to the welder. It really takes knowing someone, or having the skills and tools to DIY, to get this done. If you live in a city and don't know this person, move out to the sticks now. In a year, you'll know him -- he's out there!

I'm lucky to know a skilled metal-worker.

It took surprisingly little flame to heat, so we decided that we should make it electric. We'll get a 220-volt burner off a stove from the scrap yard (projected cost=less than $5), plus a few pounds of electrical cable at $1.50/lb. I'll add those photos when the conversion is made.

The biggest danger with this thing is it's top-heavy structure. If it were knocked over, the top of the adjustable pressure-release valve would fall off, and it would start gushing out super-hot steam, capable of melting flesh, and doing huge damage to a house.

Here she is, during testing (same as first photo):

So, it's gotta be kept upright. That'll be taken into account when designing the electric burner and stand....

Well, there you have it... a propane-tank converted into a massive bulk-quantity PC, in my neighbor's backyard, for under $200. I look forward to hearing what you folks think.

--------------------

Edited by Puma (10/29/09 02:30 PM)

Extras:

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