Pressure pot fear!!!

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Celt40

Celt40

Member
Joined
Nov 26, 2007
Messages
119
Location
Scotland UK
I have my pressure pot ready to go, I have a wooden floor in place, my mould waiting and some Pine Cones ready to be inbeded, the only thing I have not got are the B***s to put it under pressure.

I have been reading bit about how dangerous working with a pressure pot can be, that I keep puting the moment off.

What tips can you give me.

Dermot.
 
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Take the pressure that the pot is recommended to and cut it in half. Try it and check your results. If that works for what you are doing, why risk more?
 
Working with a pressure pot is not that dangerous IF you use your head.

1. Make sure all the fasteners are tight before adding pressure.

2. NEVER, EVER, NEVER exceed the manufacturers maximum pressure. As a matter of fact, don't even approach it.

3. Make sure all of your connectors and other parts are well made. Replace them with quality fixtures if you have to.

4. Just like using a band saw or table saw or any other tool, Use your head. Pay attention. Don't be thinking 5 steps ahead, just concentrate on what you are doing.
 
Russianwolf said:
Take the pressure that the pot is recommended to and cut it in half. Try it and check your results. If that works for what you are doing, why risk more?
Click to expand...

i built the Harbor Freight special like many here and usually run it up to about 50 lbs (lid says up to 80). it holds and hasn't blown up for going on 2 years. if you're worried, pressurize with nothing in it for a test... 40-50 SHOULD do the job.
 
PS: I also stole Curtis' (Mesquitman) idea and put mine in a cart, so only the top few inches are showing.
 
Celt40 said:
I have been reading bit about how dangerous working with a pressure pot can be, that I keep puting the moment off.

What tips can you give me.

Dermot.
Click to expand...


Dermot; When Dive shops "blow up" scuba tanks, they have a water bath and shroud made of 1/2"(?) steel that covers the tank. If the tank lets go, the only damage is to the operators underwear! :biggrin::biggrin::eek:

When pressurizing the pot for the first few times, I would apply pressure from a "remote location", like behind a brick wall.
 
My suggestion is to leak test all of the pipe joints on the PP system in 10 psi. increments until you have gone @ 20 - 30 psi. above your working pressure. Hold each pressure for 15 minutes before adjusting the pressure to the next setting.

Never exceed the recommended pressure recommended by the manufacturer.

I perform pressure testing on a regular basis as part of my employment and testing should not be treated lightly when using a PP.

Dave
 
It's probably like bungee jumping...

... lots of people do it, but I won't be one of them.

Now as for a PP, I plan on setting one up in the near future, but when I do I will absolutely be following all the safety measures that have been suggested on this site.

While we want to use them for casting blanks, there must be some people out there who buy, and use, them for their stated purpose - as paint pots. If they didn't work satisfactorily for that industry they probably wouldn't still be selling them.

So, if you're confident you set it up properly, follow the advice offered by the other posts and give it a try... or, you could always stand on a bridge with rubber bands tied to your ankles!... I'll be the one over to the side watching.:wink:

Dale
 
2. NEVER, EVER, NEVER exceed the manufacturers maximum pressure. As a matter of fact, don't even approach it.

And NEVER, EVER, NEVER try to undo the clamps when the pot is still pressurised ! Always make sure there is no more hissing from the open pressure relief valve before opening the lid .
 
I blew mine up. Luckily it was at light pressure and luckily, no one was around.

I think there is a fine line between "fearing" the pot and "respecting" the pot.
Respect it and its potential for damage, and you'll be good!
 
This thread is reminding me of a story (it might even be true) I heard years ago.

It seems that there was a garage that specialized in servicing trucks. They had just hired a new trainee. There was a truck tire that needed to be changed. The manager assigned that particular task to the trainee. He took a little longer to do the job than expected. When lunch time rolled around the trainee wasn't quite finished but the manager wanted to go for lunch. He instructed the trainee that when he was ready to fill the tire he was to make sure he used the safety cage. The manager returned after lunch to find the tire sitting in the middle of the shop with the air hose attached and the trainee in the cage.

Ok, I thought it was funny.
 
Thanks for all the advise.
I do respect the PP and I don't blame that trainee for getting into a cage. I think I will build an Air Raid Shelter in my back garden!!!!!!!

If you hear a dull "Thud" then that will be me here in Scotland getting it wrong.

Dermot.
 
Make an alignment mark that crosses the top and the tank. Then always line the mark up before tightening and pressurizing.

Re-seat all the fittings with pipe dope and test at a low pressure with soapy water.

Don't abuse the pot or top, obviously when pressurized, but also when not in use. -- Don't bang it around, drop it, etc.

Hand tighten the clamps only.
 
Don't stand over the pot when pressure is applied. I put mine under my table in the shop once pressure is applied.

If you can safely apply pressure remotely, that is best to do until you know the tank will hold without problems.

Don't let your guard down once the pot is proven. Continue to give it respect.
 
Been using mine for 2 years with no problems yet. I run mine to 60 psi and leave it alone for a few hours and then vent it outside to keep the smell down.
 
When the resin is under pressure will it expand. The molds I have do not have much clearnce when filled with resin. Should I make new molds that are deeper. Also what depth can I cast up to. It would be handy if I could double up my new mold depth, this will give me double the amount of blanks. Mold would be 50mm x 215mm x 75mm.
What pressure will I need to go to and for how long????

Dermot.
 
Celt40 said:
When the resin is under pressure will it expand. The molds I have do not have much clearnce when filled with resin. Should I make new molds that are deeper. Also what depth can I cast up to. It would be handy if I could double up my new mold depth, this will give me double the amount of blanks. Mold would be 50mm x 215mm x 75mm.
What pressure will I need to go to and for how long????

Dermot.
Click to expand...

Hi Dermot.

Don't be so scared, normal castings don't require any more than 20 - 30 PSI, I have never heard of a pot blow up at such pressures.

If you have a good pot, thick construction and factory rated for 80 PSI or more, you have nothing to fear using the maximum recommended pressure, I do on my Resifills (wood and resin castings) or on wood stabilization, at 80 PSI without any problems.

Using pressure pots require to learn know a few basics and those have all been expressed by other members already.

Now in relation to your question, the resin I use (PR) doesn't expand, by the contrary I see it it shrink sometimes too much, when I'm casting soft, panky or with lots of holes, crevasses wood, the wood just "sucks" the resin out, for this type of casting you need to overfill and for that you need a 30mm high (interior) mold. If your molds are too sallow, you are going to make a mess when casting as resin will overflow everywhere, particularly when you try to put the molds into the pot or on to a wooden tray specially made to accommodate a number of molds inside the pot. For single blank acrylic casting, 10mm of extra hight but if you want to make a mold that will do the wood and resin castings, the 30mm interior hight is recommended.

The 50mm high molds are handy if you want to cast bottle stoppers, making double pen blanks in a single mold, I don't thing that is a common use among resin casting people but, its is perfectly possible for some blanks a little more difficult to other mixing techniques...!

In relation to pressures and times, they vary depending on what type resins, colorants and other possible additives you will be using but, with my castings I normally do it in the afternoon and leave them in the pot under pressure overnight. In relation the pressures, that was also explained above...!

Relax, have fun with it...!

Cheers
George
 
Well I hooked the pot up to the compressor and pressed the button, and I am here to tell the tale!!!!!!
First go I lost pressure after about half an hour, I noticed the reading on the pot gauge was going down. I submerged the pot into a barrel of water. I saw bubbles comming from the base of the coupling at the gauge, and bigger bubbles from around the rim of the pot.
After I had taped the threads and reconnected I tightened the 4 wing nuts tighter and recharged to 40psi. I then plunged the pot into the water again, did not see any bubbles this time. I disconnected the pot from the compressor and left it for 2 hours.
On my return the gauge on the pot was down to 25psi. I placed the disconnected pot into the water barrel and saw bubbles comming out of the inlet coupling.

Was i not meant to disconnect the pot????
How do I stop the loss of pressure???
sould I leave the pot connected to the compressor and leave it switched on???
HELP
Dermot.
 
Yes but will the falling pressure not affect the end result???
How long will the resin need and what is the lowest pressure that will be of any use??

Dermot.
 
Celt40 said:
Yes but will the falling pressure not affect the end result???
How long will the resin need and what is the lowest pressure that will be of any use??

Dermot.
Click to expand...

Well, if you are casting acrylics only, the 24 to 40 PSI works pretty much as de-gasser forcing bubbles out of the resin and as soon as the catalyst does it job, there is, harden the resin to semi-solid state, the pressure becomes useless. Depending on the amount of hardener you used, normally 2 hours after your pour the mixed resin, you can take the molds out of the pot and let them start to dry naturally or using heating/oven type devices...!

For casting where you have wood or other base material with cracks, wholes, crevasses and other, the principle is the same but this time is very important the pot is capable to be pumped at about 80PSI at least, more expensive pots can easily accept 150PSI, the more pressure you put into the pot the better chances you have the the resin was pushed/squeezed into the smaller cracks.

While the higher pressure is particularly crucial for this type casting, keeping the blanks under that pressure for a bit longer (I like overnight), helps the resin the stay where it is, while it harden to a higher degree then the full acrylic casting will require.

Low pressures such as 10-15 PSI are capable to work on full acrylic casting with a good level of success for a 2 to 4 hour pot time, timber or other materials casted in conjunction with resin can achieve acceptable results at 40-50PSI after 3 to 5 hours.

There are no golden rules for the exact times the castings/molds need to the pressurized for, so this should give you a good starting point...!:wink::biggrin:

Good luck...!

Cheers
George
 
Celt40 said:
Was i not meant to disconnect the pot????
How do I stop the loss of pressure???
sould I leave the pot connected to the compressor and leave it switched on???
HELP
Dermot.
Click to expand...

Keep fixing the leaks as you find them. I personally would not leave the pot hooked to the compressor for fear of a failure and then the pot pressurizing to 125# (compressor pressure).

It sounds like your seal around the lid is not fully seated. What is the max pressure you have taken the pot to? Sometimes it takes high pressure to seat that gasket fully. Since you have gotten it up to 40# a couple of times, take it to 60# or 70# and see if the gasket will fully seat. The gasket may pop and release air. The gasket pops and fully seats and then air begins to leak out the lid. I tell you this so you don't soil your drawers.

If the gasket is fully seated then no pressure will release. You can also search this forum for more help on seating the gasket fully.

Biggest thing is to fix all the leaks that you are finding.
 
I left the pot at 40psi for 24hrs and it had lost about 10psi. I have tried the soapy water thing and I can not see any bubbles. I will crank it up to 60psi and see if I can hear the POP, it's okay I will keep a spare pair of drawers in the shed incase I need a quick change!!!!!!!!!!
 
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