Catastrophic pressure pot failure...my wife almost became a widow!

[MesquiteMan]

This is just a warning for those who think a HF pressure pot is safe...

I was standing just 6' to the right of where this landed. I am normally sitting right next to the pots while casting. The lid flew 15' and the guage cover flew over 30' away.

I think I will try to straighten and re-use this lid!

Here you can clearly see the pressure relieve valve that did not do any good.

This is an indentation into 3/4" baltic birch plywood made by the clamps when they flew open at lift off!


The story...

Doing a little casting last night when all of a sudden, I heard a deafening bang. I had no idea what the hell had just happened so I hit the floor, thinking maybe terrorists were attacking my shop! After getting up and checking my shorts, I find the lid to my pressure pot 6' away from where I was standing! The lid was greatly deformed and the pressure gauge was missing a portion. I ended up finding parts of the gauge 30' away! Holly smokes, did that shake me up!

Normally, I am sitting right next to my PPs while casting. Thank GOD for some reason I decided to go over to my tablesaw and cut up some blanks. All kinds of things that are normally on my casting table were all over the shop. Even the chair I normally sit in was been hit by flying debris. Thank God my guardian angel was watching over me or I could possibly have been severely maimed (other than my damaged hearing!) or even worse. Wow, what a shock!

I have made a modification to my other pots to make them last longer. I take pieces of steel bar and cut them, then drill a dimple in them and epoxy them to the lid where the clamps tighten down. This helps keep the clamp screw from eventually digging into the lid and causing problems. You can see what I am talking about on the pot to the left in the second pic.

I have been using the pot that exploded for a while now and just last night decided to add the "pot saver" mod since the clamp screws were starting to dig into the lid. Normally, I use JB weld and glue the "pot savers" to the lid and let them sit overnight. This time, I was out of JB weld so i decided that I would just use hot glue since, as far as I knew, I just needed something to hold the "pot savers" in place until the clamps were tightened.

I installed the "pot savers" and then pressured it up. I went a little past the 80# where I normally cut it off (95# actually) but have done this many times in the past with no problems. I do have a pressure relief valve but I have it adjusted so it does not start leaking until 95# or so. In this case, it did not leak at all. Everything was fine and the pot was holding air. It blew 10 minutes or so later.

What I think happened...

I think that part of what holds the lid on with these pots is the little raised ring around the lid. As the lid expands just a little with pressure, the lip prevents the clamp from jumping off the pot. That is one of the reasons I put the dimple in my "pot savers". In previous cases, the JB weld has helped hold the "pot saver" and thus the clamp to the lid since it is rigid and actually creates a good bond. In this case, the hot glue just did not have the strength to keep the "pot savers" from slipping off the lid, allowing the clamps to open and launch the lid. I am not sure how that explains the severely warped lid, though.

Anyway, now I need to get a new PP and will certainly be re-thinking my casting procedure.

 

[el_d]

Dang Curtis good thing you wer'nt in the line of fire. What pressure were you at?

 

[penhead]

Holy pressure pots mesquite man...how much pressure was on that thing..??

 

[johnnycnc]

Yikes!
Cutis, I'm glad you weren't hurt.

 

[mick]

Curtis ...first thing, Glad you're ok. Second thing it scared me as I just cast a bunch of stuff Saturday and left the pot sitting beside my lathe stand all day and evening. I shudder to think I stood beside that pot for several hours!
Just curious Curtis, how much time did you have on that pot? What do you think failed?
I think next time I cast I'll pressurize it outside and from a safe distance.
Thanks for the warning and once again I'm glad you weren't hurt!
Mike

 

[MesquiteMan]

The pressure relief valve is not gummed up at all. I think it just happened so fast that it did not have time to do it's thing.

 

[penhead]

Besides a new pressure pot...I would be needing a new pair of shorts

 

[sdemars]

Sure makes . . .

Sure makes a new or used Binks look like a good idea . . .

But then again, I have had horrible luck with anything from Harbor "Fright" . . . .

Glad you are OK . . .

Besides, it's gotta be hard to get good moderators . . .

Steve

 

[1080Wayne]

Curtis
Bunch of questions . Your usual operating pressure ? Any idea of the number of pressure cycles that pot has gone through ? Did it fail within a minute or two of being pressurized ? Do you always tighten all 4 clamps to about the same torque ? Is there any obvious distortion of one or more of the clamps ? On the pot to the left , you are using a pressure distribution plate under each clamp . Did you have those on the failed pot ? Do you always use those ?(My pot doesn`t have them .) My best guess would be that one of the clamps was not fully tightened or was not fully in on the lid . Thank you for the pictures and the warning . And I`m very glad you`re safe .
Wayne

 

[MesquiteMan]

Wayne,

See my original post for more info. All clamps were tightened equally and as tight as they would go. This pot has had a lot less use than the one in the pic next to it (my first pot). I am pretty sure the problem is due to the "pot saver" pressure distrubution plates not being properly adhered to the pot. Once again, see my original message.

(FYI, the story in the original post was not there when you posted your message. It was further down in a follow up post. I did a copy and paste to get it in the original post)

 

[Texatdurango]

Lesson #1 H/F pressure pots are rated at 80 for psi for a reason.
Lesson #2 H/F pressure pots are rated at 80 for psi for a reason.
Lesson #3 Always remember lessons #1 and #2

What were you trying to do... make some worthless steel blanks and needed the extra pressure to get the resin into the pores of the steel bars?

I think you just want to show off your HUGE shop :biggrin:

 

[MesquiteMan]

Yeah, but Johnnyjarhead had one up to 200# with no problems! I don't think it was the pressure. I still think it was the "pot savers". I guess that is what I get for trying to save my pot, huh?

 

[jeff]

Wow, Curtis. Incredible story. Glad you're ok.

You have some heavy benches in your shop? How about setting the pot under one of those while you're casting?

I bet the lid is warped because the clamps didn't disengage simultaneously. It doesn't take much of a deformity to set in motion a few millisecond chain of destructive events. One clamp slips a little, the lid deforms slightly, then boom! Lot of force on that thing! What's that, a 12" lid? Every PSI is 113lb?

Did I see 80PSI in another post? 9000lb on that lid.

 

[mbroberg]

I am sure glad you are OK. Thanks for sharing this story. This serves as a scary reminder that one can't be to careful, even when doing something that has been done many times before.

 

[PTownSubbie]

Curtis,

I am glad you were not hurt. That could have been really bad. After hearing your story, I think I will do as Jeff hinted....Put my pot on the floor under a bench to minimize the chance of taking my head off.

BTW, I also agree with Jeff that the warping is likely due to the clamps not releasing at the same time. If you were close to it, you might have seen the savers slipping and been able to release the pressure before it blew. But then again, better off you weren't close to it!!

I have had my seal blow out once but never anything like yours!!

 

[jkeithrussell]

Really glad you weren't standing over that thing when it blew. Close call.

 

[JimMc7]

Goodness -- glad you're ok! For once, glad I'm a newbie and still completely satisfied buying blanks others have made!

 

[jedgerton]

Curtis,

If the pot saver sits on top of that outer ridge, it would focus the down force from the clamps on the two inner corners and the outer ridge. Could the pot saver have deformed the outer ridge and weakened it enough to allow it to bend at that point? I know it wouldn't take much deformation to weaken those lids and if so, it works much like an avalanche, feeding on itself. Just a thought.

John

 

[alphageek]

Holy Cow Curtis! Definately a good thread for ANYONE who uses a pressure pot. We keep trying to share the dangers that a shop COULD be... This is one I'll be most don't think so much about.

Glad you were ok.

 

[tool-man]

I am so glad you escaped any injury.

Let me second the above comment - if the pot is rated as 80 PSI max, don't exceed that pressure. It matters not that someone else told someone he had exceeded that limit without incident.

The small pieces of metal under the screw clamps - are those what you call "pot savers?" I can see a potential problem. If the lid even so slightly deforms, that piece of metal could shift resulting in uneven hold down pressure. The clamp with lesser hold down pressure would then allow increased lid deformation, and a cascade effect might follow.

If you need to cast at 80 PSI I would not use a pot rated at 80 PSI. I know we all hate to spend the money, but I would suggest you look into commercial duty pots that have a higher pressure rating.

These comments are merely my opinions, and I intend no criticism whatsoever. They are worth exactly what you paid for them.
Andy

 

[helgi]

Pot failure

Mesquiteman,
I'm glad you are not hurt and no serious damage to your shop or equipment.
upon reading your post I would suspect that you have had a clamp failure IE,
metal fatigue, as you say you placed keepers under the screw down clamps and the pressure comes from below and pushes the lid up. So the keepers either contributed to the clamp failure or the pot lid is made from thin stock and warped under pressure with the almost dissastrous result. I would check the holddown clamps very thoroughly and please do not ever use that lid again you are asking for a major headache doing that. Also maybe the tought should be to check out for a refurbished devilbiss or binks pot but in the meantime take a look at those pots and compare the lids on those pots to the one your thinking of buying. Or if nothing else can refrain you from buying a HF pressure pot" do you need that much pressure on a pot that is not used other than static pressure"? When in all my years of spray painting (35----40)the pots were under lots of pressure but it was continually bled off not so when you cast. Thus greather change of metal fatigue.
Again thank heaven you did not get hurt, lots of luck in your further endevours.


Helgi.

 

[PR_Princess]

WoW Curtis!! I am glad that other than having the bejesus scared out of you that you are OK!

One of the idioms of this forum is "thanks for sharing". In this case I think that phase takes on a whole new meaning!!!



BTW... I am assuming that you will be doing your own laundry?

 

[wdcav1952]

Curtis,

Let me also say thank goodness you weren't hurt! That definitely was a scary experience! I would be totally gun shy of pressure for a looooooong time after that.

Thanks for sharing. I won't dilute your thread, so I'll post another time about my scary experience (not in a shop)

 

[MesquiteMan]

If you need to cast at 80 PSI I would not use a pot rated at 80 PSI. I know we all hate to spend the money, but I would suggest you look into commercial duty pots that have a higher pressure rating.

Andy, the HF pot IS rated at 80 psi.

I have been casting for 3 years now and have cast who know how many blanks. The pot on the left in the pics is my original pot that has been through 3 years of hard use. I do agree that it may be time to look into something more robust since I do cast as a business and not just for the fun of it.

I still do not think it is necessarily the pot's fault. I still think it has something to do with my modifications and the hot melt glue. The pot on the left has had the "pot savers" on it for a year now with no problems.

 

[CaptG]

Curtis, glad you did not get hurt. I like how you recessed your pots in the bench. I may have to try that and add a hinged box lid over the top to "absorb" any potential fragments.

 

[MesquiteMan]

Might need to make that lid out of 1/2" steel! Not sure wood would do any good! Heck, the explosion blew the top off my wood mold rack that I use. I still can not find that piece! Than goodness the resin had been in there 10 minutes and Alumilite sets so fast or I might be cleaning up resin from all over the shop!

Heck that is a good new reason to use Alumilite!

 

[Dan26]

Glad you're not hurt. Great story, though. Are you getting a hard hat for Christmas? Need to protect the melon, you know.

 

[TomW]

Curtis,

Wow... Now you know why I left the last Central Texas meeting before the casting demo..

I'm glad you are ok.

Tom

 

[OKLAHOMAN]

Might need to make that lid out of 1/2" steel! Not sure wood would do any good! Heck, the explosion blew the top off my wood mold rack that I use. I still can not find that piece! Than goodness the resin had been in there 10 minutes and Alumilite sets so fast or I might be cleaning up resin from all over the shop!

Heck that is a good new reason to use Alumilite!

Curtis, first thank goodness your OK, I think your putting steel strapping on each clamp is a great idea, that just went wrong.

Don't know about that as I started using Don's no pressure system with PR on all blanks except worthless and cactus, and will experiment with cactus not using pressure.

 

[greggas]

About 4 years ago I had a PP do the same .....the result of a faulty pressure relief valve. Scared me enough that I moved my replacemtn PP into the same plywood lined closet that I keep my dust control in. This way if it were to blow again I think I am safe with two layers of 3/4" CDX.

Glad you escaped injury.

 

[Fred]

Definitely a good example of how things can go wrong.

Curtis ... lose the metal bars as I agree with what Jeff says ... one slipped and everything went downhill from there.

The pots are cheap enough that using the metal pieces to save the lid from whatever it is you are trying to save them from is just not worth the pain and damage that comes from an accident.

We do need you around a lot longer ... Glad your hard head was not looking down when it blew...

 

[TellicoTurning]

Curtis,
That's it.. if the master caster has this kind of catastrophe, then imagine what I could do... I think I continue to buy my cast blanks from they guys who are willing to take the risk... I'm really much too pretty to get smacked in the kisser by one of those exploding pots.:biggrin::biggrin:

I'm glad your guardian angel sent you over to the table saw... it's nice having one to look after you.

 

[BRobbins629]

Glad you're okay. That must have been a real scare. Hope you have changed your mind from several years ago where you said:

"As far as the safety of casting at 60 psi...that is a real stretch, no disrespect intended, Bruce!"

 

[DCBluesman]

I'm glad to read that you are unharmed.

 

[RAdams]

Lesson #1 H/F pressure pots are rated at 80 for psi for a reason.
Lesson #2 H/F pressure pots are rated at 80 for psi for a reason.
Lesson #3 Always remember lessons #1 and #2

What were you trying to do... make some worthless steel blanks and needed the extra pressure to get the resin into the pores of the steel bars?

I think you just want to show off your HUGE shop :biggrin:

I totally agree! :tongue:

I would have to agree also with our trusted Mod, in that the failure was the pot savers. If i was going to add them to my pot, i would cut a little bit off of the back leg of the saver thingy, to change the angle to match that of the lid. In fact, if the angle was correct, the hot glue probably would have worked. Still kinda lost as to why you would go to 95 elbows. I would just flat out be nervous to be in the same room with that much pressure in a home engineered HF product. I get nervous around mine when i let it go to 50.

 

[leehljp]

Thanks for the lessons on what not to do. As others said, we sure are glad that you are OK. I too have wondered about the screws digging into the lid and even considered "caps" on the screw with smooth bottom - similar to C-clamps swivel base. But now I am certainly NOT going to try that.

 

[Druid]

Curtis,
Glad to hear your ok, must have been that Hat I sent that saved your butt.... or maybe that's why you "hit the deck" so quick after hearing a loud bang! Guess I need to put that Kevlar shirt in the overnight express:biggrin:
Seriously, thanks for sharing and may the guardian angels keep watch.

 

[Glass Scratcher]

Curtis,

Glad you were not injured.

Now to follow with what George said but from the manual. For the safe operation of the HF #93119 pressure paint tank, the recommended operating pressure is 30 - 70lbs. The MAX pressure (or more accuratly, the OOOps pressure rating) listed on the lid is roughly 10% over the top end of the operating pressure range. To continually run the HF pots over 70lbs is- well just plain waiting to be a Darwin Award recipiant.

If I remember the numbers I ran some time back, at 40psi the upward Force on the lid is 7tons.

 

[MesquiteMan]

Charles,

This may be and I would be a good candidate for the Darwin Award with some of the things I have done in my life!

I still stand by my assessment that this failure had nothing to do with the pot itself but rather my modifications. My other pot has been in use for 3 years with no problems at all. I do think, however, that I will be investing in better equipment.

 

[jppensplus]

Curtis--

Glad you were not in the line of fire and escaped injury!! Thanks for your critique of what did and what may have gone on to contribute to that explosion!!

JP