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The Corroboree
Ed.

G'day from S.E. Queensland

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Hi everyone, just a quick intro to say hi, I am in S.E. Queensland and only just recently started to get interested in growing mushrooms. I used to grow orchids and bamboo and when I closed the business I threw out most of my equipment thinking I will never use it again, so now have to almost start from scratch, anyway I should have finished building an electric 250L pressure cooker by early next week and cleaned and sterilised my small insulated room for the growing section. I also have a large glove box that needs some attention to get that up and running as well.

I originally got interested by wanting to grow Lion's mane (Hericeum arenacium) for it's medicinal benefits, but soon found out that we only have the coralloides version in Oz, so will try and find some spores of our species which may do the same, apparently they turn up occasionally in Mary Cairncross park in Malaney Qld. so I may have to go looking there, I think a former member here called Punkin might have had some of the erinaceum but he seems to have disappeared from this forum, anyway in the meantime I will try and grow some Oysters in a couple of colours, I am mainly interested in wood loving species as I do a bit of woodwork and sometimes I have a pile of hardwood sawdust and chips which I usually dump in my garden, this way I can put it to better use. So I now have to brush up on new skills and methods and hopefully grow a feed of mushrooms.

Cheers

Ed.

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Welcome to the forums mate :)

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hi ed

great to hear, sounds like you will be very succesful with ur ventures.

best of luck.

hail an well met

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G'day Ed, welcome to the forum.

You mentioned you're making a 250 litre PC. That's enormous by most peoples standards. Do mind giving us some details of how you built it ?

I saw a pic of a PC Punkin made from a beer keg on his site. I think he said it had an operating pressure of 25 psi or there abouts. I'd be scared to be in the vicinity of something like that if the welds weren't X rayed. As you said I don't think Punkin comes here anymore.

I'd love to see your PC or just find out a few details of how you've constructed it.

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just save your time and get a all american its well built .Sally is right make sure the thing is safe .

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Hi Sally, Before I begin I should do the usual disclaimer, that I did this for my own use and my own skills as a welder and if anyone does do this or copies what I did then they accept all respossibility and liability should something go wrong, I am explaining this as to what I did and I make no guarantees that this may work for others or be safe. Now that's out of the way:

My previous one I made out of a 60lt propane gas bottle and heated it by putting a 3 burner gas barbeque under it which took a while to heat up as the steel bottle was exposed and had a tremendous amount of heat loss because of this fact. This one is based on a 250L electric hotwater heater and I used this size so should I want to, I can put in a 110cm log and sterilize it and it has the benefit of being well insulated so the heat loss will be significantly less. The advantagous of using a gas bottle from a safety point of view as against the hot water heater is that the gas bottles use much thicker steel and have a much higher working pressure than the hot water service, there by having a greater safety margin, but no insulation. Having said that if you go for a hotwater heater cylinder, you have to make sure that the steel hasn't been compromised and corroded and is structurally sound.

Most hot water heaters are rated to about 850-1000Kpa which is approx 125-145PSI about 8-10 times more than the pressure that a PC uses, allowing for the fact that you are modifying the cylinder by putting in a door and using air/steam instead of water, (water is safer as it tends to leak rather than explode in the event of a major cylinder rupture). Bear in mind that 15PSI is a relatively low pressure, what makes it dangerous is the tank diameter, so the bigger the tank the more force is on the walls trying to expand and turn it into a balloon and burst open.

Back to the story, I have been welding for over 40 years so don't have any concerns with my welds not being x'rayed to prove that it won't go bang, at least not for my working pressure. If I was working on something commercial or higher pressure than I absolutely would have them tested as I could not afford the liabilty should something go wrong. Also if that was the case I wouldn't be using a used hot water service and would use new steel and insulate it after it was built and tested. Provided that you put in the pressure safety valves they should keep the pressure down to the safe working level. Can't count the number of times the foam caught on fire when I welded near it though.

Now I made this one to operate with the tank on the side so built a stand out of some scrap pipe I had, then cut a diamond shape door opening with rounded corners into one end of the heater tank with a plasma cutter. Inspected the tank for corrosion and proceeded to make the actual door out of 6mm plate about 25mm bigger than the opening, the reason for using an oblong shape is that the plate can go in through the wider part, then a 90 degree rotation and the plate can't come out. The door is designed so that as the pressure builds inside the tank, it tries to push the door out through the now smaller and reinforced hole. Where I cut the hole out I reinforced the entrance with a piece of 40mm x 4mm flat bar bent to the inside hole shape and welded the two ends together. Then plasma cut another piece of plate that was 25mm larger than the welded flat bar which will be the mating surface for the seal of the door, welded that to the formed and welded flat bar. So basically it is a piece of angle steel section formed to the shape of the door with the smaller angle on the inside of the tank. (I don't have a angle iron bender) Cleaned it up and welded it to the tank opening. The actual door has two pieces of flat bar also welded to the outside to help position the door so it lines up in the door mouth.

For the door, I welded a 10mm x 60mm bolt to the outside, I use a piece of hardwood with a hole drilled through the centre which I place over the bolt and over the door lip which when tightened squashes the nitrile seal flat against the door seal angle. I tack welded a strip of stainless 6mm round rod just larger than the door hole, but smaller that the ouside flange of the door reinforcement/seal, and then Sikaflexed a piece of 8mm round nitrile rubber on the outside of the stainless rod. The rubber you can get from most bearing supply stores and you cut it to length and super glue the ends. (about $6/mt), glueing that round nitrile seal to the flat door plate stops the seal from moving around and also prevents the seal from being forced out through the 2mm difference of the s/s round rod and the thickness of the rubber seal. This sound complicated but the pics will make it clear.

Next I welded up a piece of 125mm x 3mm thick by 500mm long SHS for the main heating tank that houses the heating element, added a piece of pipe to one end plate and welded a piece of 10mm flat bar with 4 holes drilled and tapped to it to fit the 3600 watt heating element through it. Added 2 bits of 50mm x 75mm x 2.5mm RHS to one long side and cut out the corresponding holes at each end of the main tank. These bits will allow the water and steam to flow back and forth from that heating chamber into the main tank, also added a drain hole and tap to the bottom of the heating chamber, for easy drainage and pressure relief.

Used an angle grinder to cut out 2 oversized bits out of the heater tank sheet metal skin and removed the insulation underneath to provide access so that I could weld the 50mm x 75mm RHS to the wall of the heater cylinder. Plasma cut two holes through the tank heater wall itself so the water and pressure can flow through the system.

Water heaters come with handy plug socket holes which suited my purpose for fitting in guages so I positioned the heating chamber at the bottom of the tank and the plugs ended up on top. The temp guage has a 200mm sender so made up a bit of pipe welded up on one end and welded the other to a drilled pipe plug and fitted it to the socket nearest to the door. Made up another short bit of 40mm SHS with a bit of threaded 1/2" pipe to go to the other end of the tank and screwed that in. That one holds the pressure valve and safety weight. I will have two, one is a weight and the other a spring loaded one which still has yet to arrive. The first one I ordered was delivered in the wrong size.

For controlling the heating element I used a simmerstat (MP101 it's a 15A) from an old stove, fitted it to a plastic enclosed box and used 2.5mm wire lead.

Welded it all up and pressurised it to 36 PSI and squirted soapy water on all the welds, found a couple of leaks which is to be expected with MIG welding, depressurised it, fixed up the leaks, repressurised it and now good to go, no more leaks. I cut out the sides of the plastic box and heat welded some stainless mesh to allow some air flow as when I tested the PC I ran my infrared meter over the switch terminals and they were hotter than I liked, probably within the limits of the switch but better to be safe. The switches on ovens are not completely enclosed so heat build up in the switch could possibly be an issue if the heat can't escape.

So that pretty much sums up the build, just have to insulate the lower heating element tank and get some insulation for the door as well. It's been a long post and as I said at the start, I built it for my self and accept no responsibility if someone copies it, it isn't pretty but it works and cost me very little apart from my time as I used bits that were in my shed laying around. Still waiting for the last pressure valve and if it doesn't arrive soon I may have to build one myself. If I do end up making one I may make it to relieve the pressure at 25PSI as a safety factor in case the weight vent hole gets blocked. The pics, and there are quite a few are in no particular order. Hope this helps.

Cheers

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Edited by Ed.
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Hi Ed, welcome mang. Always nice when new bies say hullo and do a meet n greet in this sabmaelstrom of entheology that is undefined, unbespoken but with a grain of composure - is easily understood.

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Nice fabrication skills, you want a job? LOL

id like to say please dont try this at home people, unless you got years and years of pressure welding and fabrication experience like this guy

Welcome to the forum Hillbilly

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Thanks for posting all the details and pics ED.

I just assumed that you'd made it out of stainless for some reason. As you'd obviously know mild steel is lot more forgiving when it comes to fatigue and cracks developing than stainless, so X-raying it would be a bit of overkill for your design.

What sort of relief valve are you using ED ?, I was looking at some the other day and I didn't see many rated to that temp that would pop off at such a low pressure/temp. Most of the valves I saw were either 60 psi plus or they were very expensive.

Edited by Sally

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Thanks to everyone for the welcome, yes mild steel is more forgiving but the working pressure is quite low so the difference in stainless vs mild for this wouldn't make a lot of significant differance, this is an old water heater which cost me $20 bucks at a recycle plant and even came with the heating element included. I originally set it up as a vacume chamber to do vacume forming but got side tracked and never did anything with it so this was a good solution.

Making one out of stainless would cost a small fortune by the time I bought a sheet of it and got somebody to roll it, I also would have to find 2 hemisperical caps to put on both ends and those things are really, really, big bucks. The alternative would be to use flat plates but then I would have to add some serious reinforcing on the ends and then add a shell and fill it with polyurethane to insulate it. All this vs $20 well you know which way I went. :wink:

As for the valves I just went on ebay and bought a pair of ones that fit readily avalable store bought pressure cookers, they work slightly different to the weight system where the pressure in the cooker pushes against a known weight and as the pressure builds it lifts the weight off a tube and the pressure reduces, the ones I bought just have a spring in a tube that pushes against a cap over a hole, as the spring reaches a certain pressure it is forced to open and again reduces the pressure. The weight is more accurate as it is constant regardless of temp, whereas springs when heated up may slightly change the effectiveness of the pressure release, but overall would have a minimal effect and for our purpose it would be negligible.

Either way the temp in the tank is related to the pressure so at:

1 Bar or 14.69 PSI ambiant pressure is 100 degrees C, (Normal boiling water at sea level)

+1 bar it is about 120 degrees C.

+2 bar it is about 135 degrees C

The fun begins if you suddenly release the pressure to atmospheric (as in a blown seal or a split in the tank) when it has reached boiling point at 2 or 3 atmospheres ie; super heated steam and water, remembering that we generally calibrate gauges to zero at normal atmospheric pressure it actually is 14.69 PSI already. So that when the pressure cooker reads 1 Bar there is actually 2 Bar inside. What I am trying to say in a long winded way is that the temp variation is only about 35 degrees C.

So, as I was originally planning on raising the pressure up by one Bar, the normal pressure cooker spring valves would do, and they are very cheap. I think I paid less than $5 for the pair delivered, too bad I received ones with the wrong thread size after waiting for them for 3 weeks. But if I have to make one now on the lathe to fit the existing fitting I welded in place, I might as well make an adjustable one that will go up to + 2 Bars, which means I would have to plug the weight tube or somehow add more weight to it, otherwise it will continue to release pressure at the +1 bar. another alternative is to just reweld a different fitting to take this valve which is probably the simplest solution. Hope this sort of makes sense.

But I admit I also saw the prices for pressure valves and some of them were really expensive. As this is just a cheap skates way of making a large pressure cooker, I already had the gauges so it will have cost me under $50 to build a 250L PC, the $5 pressure valves would have been good.. trouble is I am running out of time and want to get started. Only reason I built a large one like this was in case I want to sterilize a log and the time to build and the cost difference is also the same.

Cheers

Ed.

Edited by Ed.

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Thanks for all the info ED

If it was stainless, it would have needed a second mortgage to pay for the materials, plus all the gas you'd need to purge it before each weld.

Are you an engineer or a fitter/welder ?

You really seem to know your way around a metal shop and you mentioned using a lathe in your last post.

Don't feel obliged to give away personal details if you don't feel comfortable though.

Cheers mate.

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Welcome Ed.

I didnt understand half of what you wrote but i enjoyed every word of it :-)

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Hi Sally, No problems, Definetly not an engineer but I have welded and made stuff professionally and as a hobby for most of my life, I have a reasonably equiped "man cave" with several welders and a largish metal, wood lathe, metal and wood bandsaws ect. ect. mainly 3 phs gear, so it keeps me busy and should I need something I don't have, I can usually make something in there to do the job. Might not be pretty but it works! In fact I have crammed so much gear in there that my missus can't park her car in there any more, she is not happy! Actually it is hard to just see the floor, I have just started to do a complete reorganisation in there as I am tired of tripping over stuff. Incidently you also seem to know "stuff" so I take it you also have some experience in metal work?

Cheers

Ed.

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