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Pressure Pot - Explosion Protection

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Forum topic by Jeremy Wright posted 01-14-2020 10:48 PM 385 views 0 times favorited 13 replies Add to Favorites Watch
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Jeremy Wright

2 posts in 9 days


01-14-2020 10:48 PM

Topic tags/keywords: pressure pot casting safety

Hi, all.

This is my first post. Lumberjocks has been incredibly helpful in my growth as a hobby woodworker.

My wife and I have been casting resin, and due to the bubbles we get in our casts we decided to try casting in a pressure pot. We got the Harbor Freight pot most everyone is familiar with and converted it. I also replaced the gasket with one off of Amazon and spread automotive silicone grease around the lip of the pot and in the groove the gasket goes in before inserting the new gasket. It seems to be holding air pressure, maybe a slight leak.

Here’s why I’m writing this post:

I must have read a hundred horror stories on the net about these things blowing up and I’m nervous. Presently, I have it sitting in my shop vac silencer with the door latched in case of an explosion. That’s not a permanent solution, though, as I want to use the silencer for what’s for.

https://www.flickr.com/photos/[email protected]/49385097818/in/dateposted-public/

Would it make any sense to build some kind of box to contain the pressure pot in case there’s an explosion? And if so, can I run the air in, gauge, and safety release out the box so I don’t have to open the box to pressurize and depressurize? I know next to nothing about air tools other than to be careful with them.

https://www.flickr.com/photos/[email protected]/49385563706/in/dateposted-public/

I admit, I could be worrying too much about this. I’m worried about someone getting hurt, or something in our garage getting torn up (like the garage door or a car window or something).

One other thing, I saw multiple posts where people were casting at 60psi. The max on this HF pot is 60psi and frankly, I don’t want to go that close to the maximum limit for this cheap Chinese made pot. We’ve been using Art Resin and are about to try Total Boat. I’m hoping that I’ll only need to go up to around 40psi. Again, could just be my paranoia.

Any and all input is greatly appreciated. Thanks!


13 replies so far

View DS's profile

DS

3360 posts in 3027 days


#1 posted 01-14-2020 11:18 PM

I hadn’t heard of using a pressure pot for casting, but, we used to use a bell jar and draw vacuum to remove air bubbles in industrial resin castings back in my electronics mfg days.

Sorry that I’m not more helpful, but, to my experience, it seems a little backwards. (pressure vs vacuum)

I will be monitoring this thread and maybe this old dog can still learn some new tricks.
Good luck!

-- "Hard work is not defined by the difficulty of the task as much as a person's desire to perform it.", DS251

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Andybb

2376 posts in 1210 days


#2 posted 01-14-2020 11:21 PM

40 psi is fine for resins like Alumilite, Total Boat etc. Your safety is the over pressure relief valve. I thought the HF max is 50 so I never go higher than that regardless. Other than a concrete wall not much is going to stop shrapnel from an exploding metal container. If you want to you can buy a better relief valve and replace the HF one. Even if you put it in the silencer you are going to need to see the gauge as you fill it so if it’s going to explode that’s when it’s most likely to happen IMO. I never put my face or body over the lid as I think the fittings are the weakest link. I also don’t like the hard sealant HF uses on the fittings and resealed it with a more flexible non Chinese sealant. I also always keep it on the floor so it doesn’t fall off of a table and explode. Also set your compressor for a max of 50psi when filling it. I like to be able to see the gauge so that I can give it a little boost if the pressure drops a little after a few hours. It seems to hold pressure better if I also give the latches a half turn with a wrench after I get it as tight as I can by hand.

Do you have a link to the gasket you got off of Amazon that fits it? I should probably do that.

-- Andy - Seattle USA

View Gene Howe's profile

Gene Howe

12000 posts in 4035 days


#3 posted 01-14-2020 11:36 PM

You’ll be safe at 40 to 45 PSI. If your compressor can be set at 45, that would be another safety point. I’d also like the Amazon link for that gasket.

-- Gene 'The true soldier fights not because he hates what is in front of him, but because he loves what is behind him.' G. K. Chesterton

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Andybb

2376 posts in 1210 days


#4 posted 01-15-2020 03:22 AM

Sorry that I m not more helpful, but, to my experience, it seems a little backwards. (pressure vs vacuum)

I will be monitoring this thread and maybe this old dog can still learn some new tricks.
Good luck!

- DS


The pressure squeezes the bubbles down to non existence while the resin cures. People use vacuum for stabilizing punky wood to suck thinner resin into the wood and displace the air. Also for sucking the air out of silicone for making molds.

This is what he's doing.

-- Andy - Seattle USA

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Andybb

2376 posts in 1210 days


#5 posted 01-15-2020 03:46 AM

I d also like the Amazon link for that gasket.

- Gene Howe


Maybe this? Gotta go measure mine.

-- Andy - Seattle USA

View Nubsnstubs's profile

Nubsnstubs

1662 posts in 2337 days


#6 posted 01-15-2020 04:05 AM

Jeremy, I’ve been exposed to pressure pots since I was 15 years old, or since 1962. All those years, I’ve always heard of them exploding if they get too much pressure, but have only witnessed gaskets giving way, and a loss of air pressure. If the tank was built badly, it would most likely rupture at a seam, and all that would happen is the air would escape with whatever chemical you had in it. The Explosion term is used to keep most people from going to extremes and really do something stupid.
This is my opinion and should not be taken as scientific fact. I’m only trying to have you respect your tool without fearing it. ................ Jerry (in Tucson)

-- Jerry (in Tucson) www.woodturnerstools.com

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Andybb

2376 posts in 1210 days


#7 posted 01-15-2020 04:31 AM


Jeremy, I ve been exposed to pressure pots since I was 15 years old, or since 1962. All those years, I ve always heard of them exploding if they get too much pressure, but have only witnessed gaskets giving way, and a loss of air pressure. If the tank was built badly, it would most likely rupture at a seam, and all that would happen is the air would escape with whatever chemical you had in it. The Explosion term is used to keep most people from going to extremes and really do something stupid.
This is my opinion and should not be taken as scientific fact. I m only trying to have you respect your tool without fearing it. ................ Jerry (in Tucson)

- Nubsnstubs


+1 Another reason those pots have rounded bottoms so there is no seam. The last HF pot incident I can find is over 12 years ago.

-- Andy - Seattle USA

View Jeremy Wright's profile

Jeremy Wright

2 posts in 9 days


#8 posted 01-15-2020 02:33 PM

AndyBB,

I see, so it seems like putting it in a wood box would just make more shrapnel. I try to reach over when filling it with air instead of leaning over, as I’ve been scared to get too close to it. I did replace the HF pressure relief, the one that came with it was really crappy.

Here’s a link to the replacement gasket; it fit perfectly: Paint Pressure Pot Gasket

and Silicone Grease

Jerry,

I appreciate it. I don’t want to be afraid of it, and I do feel safer after getting this info.

Thank you, all, for your help. It still amazes me some days that I live in a time where I can easily learn from people all over the world.

View Andybb's profile

Andybb

2376 posts in 1210 days


#9 posted 01-15-2020 03:23 PM

As Jerry said the word explosion is a little dramatic like a grenade or bomb. I think you have nothing to worry about especially if your safety valve is operational and you keep the pressure under 50 psi. Just be smart and enjoy casting. Don’t shoot it or drop it and your fine.

Thanks for the link.

-- Andy - Seattle USA

View PaulDoug's profile

PaulDoug

2300 posts in 2310 days


#10 posted 01-15-2020 04:05 PM

Do you worry about the tank on your compressor exploding. That can happen also. You might want to look for precautions on how to prevent that also. Just to be safe. I think maybe explosions of either is very rare, but a possibility to be aware of.

-- “We all die. The goal isn't to live forever; the goal is to create something that will.” - Chuck Palahniuk

View ibewjon's profile

ibewjon

1174 posts in 3400 days


#11 posted 01-15-2020 04:16 PM

I have seen an air compressor tank that exploded, or maybe ruptured would be a better term. I do not know if there were small pieces sent flying. It had not been drained regularly and was not in good condition. I wish I had a picture to post, but it before camera phones. I added a second relief valve to my compressor, and drain the tank at least weekly.

View Andybb's profile

Andybb

2376 posts in 1210 days


#12 posted 01-15-2020 05:28 PM

I wouldn’t worry about the pot or compressor exploding. Just start casting.

Good luck.

-- Andy - Seattle USA

View Gene Howe's profile

Gene Howe

12000 posts in 4035 days


#13 posted 01-15-2020 09:38 PM


I d also like the Amazon link for that gasket.

- Gene Howe

Maybe this? Gotta go measure mine.

- Andybb


Thanks, Andy. I see that someone asked if it fit the HF pot and the answer was yes.

-- Gene 'The true soldier fights not because he hates what is in front of him, but because he loves what is behind him.' G. K. Chesterton

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