# Casting Pressure Chamber??



## Nubsnstubs (Dec 2, 2017)

I think I already know that this idea I have will work, but just looking for more feedback or suggestions from more experienced people on here.

What I need to do is cast a few pieces that are over 12" long. My current pressure pot is only 11" tall , so after looking for some of the metal tubing I purchased years ago for making pressure chambers and couldn't find it, I decided that 4" PVC pipe can do the job. I know that 1/2" schedule 40 is rated at 600 psi. I'm going to use 4" pipe and am guessing the pressure would be about 200 - 400 psi. It looks like using a 70-80 pressure should work. I will also place the 4" pressure pot in a large tube I have so if it explodes, shrapnel will be contained 

All my glue joints on the fittings will also have screws to help hold the pieces together. The only fitting that won't be glued is the top screw cap that is seen on your plumbing clean outs in every home in the country. I'm going to wrap the threads with Teflon tape so I'll be able to remove it when the casting is set.

All pieces I cast will be in their own individual PVC tubes so the inside of the 4" should always be clean after each casting. 

Am I delirious or does this sound viable??? ............ Jerry (in Tucson)


----------



## duncsuss (Dec 2, 2017)

Jerry, somebody on IAP asked a similar -- but different in one important respect -- question on IAP when he wanted to cast some pen blanks.

The major difference here is the diameter of the schedule 40 pipe you are proposing to use, they are talking 3/4" and 1", you are talking 4". The burst-pressure rating varies with the diameter of pipe (larger pipe, lower burst pressure rating) -- don't guess the pressure rating, verify it. Even double-sleeving it into another pipe might not protect against shrapnel.

Once you know you've got the safety aspects covered, I think it's a great idea and hope it works out for you.


----------



## The100road (Dec 2, 2017)

@Sprung


----------



## rocky1 (Dec 3, 2017)

Having spent 14 years managing a rural water system constructed of oh... 530+ miles of PVC pipe, I can tell you this. 

1.) LEAVE THE SCREWS OUT OF THE EQUATION!!! You are creating the bomb you're trying to avoid right there!!! 

Attempting to screw the fittings together/to the pipe, destroys the structural integrity of the PVC, and weakens the pipe drastically. That WILL cause your pipe to fail, I guarantee it! 

2.) PVC pipe can be purchased by specific pressure rating in a commercial environment. Find out who the local municipality buys their pipe from and you should be able to buy PVC pipe in class 100, 120, 160, 200, 250, 280... They all use the same fittings, wall thickness on the fitting and their design usually push them up there in the 300 - 400 PSI range. The difference in pipe classification is attained by varying wall thickness on the pipe, outside diameter remains constant so they can use the same fittings, inside diameter is minimally reduced as pipe classification increases. 

3.) That having been said... Pressure rating on 4" schedule 40 PVC pipe, as you would find in your local hardware store, Lowes, Home Depot, is just over 200 PSI. So you're well within safe operation of the pressure chambers described, at the pressures suggested. I wouldn't be even remotely concerned. 

See top of page 2 for rated pressures should you deviate from this design - 
http://www.cresline.com/pdf/cresline-northwest/pvcpressurepipe/CNWPVC-40.pdf 


4.) While I wouldn't be the least bit concerned about the pipe itself withstanding that pressure, all of the pipe explosions on water systems that I know of were caused by damage to the pipe under pressure. What does it take to damage it? Very little honestly, but we were typically running higher pressures, and carrying water which behaves differently than air. Dropping something on it, dropping it under pressure, it really doesn't take much. You can hit it with a hammer and split it for 8 - 10 ft., if it doesn't explode. There putting it inside another tube might be wise. Blow pressure down on your chamber before moving it by all means. 

Glue your chambers up a week in advance to allow the glue to fully cure before use.

Reactions: Informative 2


----------



## Nubsnstubs (Dec 4, 2017)

rocky1 said:


> Having spent 14 years managing a rural water system constructed of oh... 530+ miles of PVC pipe, I can tell you this.
> 
> 1.) LEAVE THE SCREWS OUT OF THE EQUATION!!! You are creating the bomb you're trying to avoid right there!!!
> 
> ...




Thanks, Rocky. I had the same thoughts as your knowledge imparted. (?) My biggest problem so far as I went to HD, bought all the stuff, and after I wrote the above question, I realized I purchased all ABS pipe and fittings. The 4" pipe specifically states, "NOT FOR PRESSURE". Back to HD for a refund, and will get the PVC I asked about. 

The screws I mentioned was to just act as something like a grub screw used on a lot of tools with handles and such, like hand wheels on a tailstock. If that's a no no, I'll take your advice, and not use them. Thanks for that info.
............ Jerry (in Tucson)

Reactions: Sincere 1


----------



## rocky1 (Dec 4, 2017)

Definitely a no no Jerry. The screw imparts pressure that will likely cause the pipe to split. I wouldn't anticipate the bomb effect, but it is possible. I'd be more inclined to believe it would simply split as pressure came up and the pipe stretched, which yes it does expand under pressure, but it could set up a stresses fracture that resulted in catastrophic failure under full pressure. No screws necessary or advised. I honestly believe you're more apt to blow it up with the screwed in it than without.


----------



## Nubsnstubs (Dec 4, 2017)

rocky1 said:


> Definitely a no no Jerry. The screw imparts pressure that will likely cause the pipe to split. I wouldn't anticipate the bomb effect, but it is possible. I'd be more inclined to believe it would simply split as pressure came up and the pipe stretched, which yes it does expand under pressure, but it could set up a stresses fracture that resulted in catastrophic failure under full pressure. No screws necessary or advised. I honestly believe you're more apt to blow it up with the screwed in it than without.




Ok, plastic is out, and steel is in. Just went by a local scrap yard and got myself a piece of 1/4" x 6 x 16 1/4" steel. I have total access to a welding shop, so I'll just have him weld up the bottom and then some lugs to accept some bolts for the lid. Instead of questionable plastic, I'll now have a steel chamber. I feel better about it now. Thanks for your insight, Rocky. ............... Jerry (in Tucson)

Reactions: Like 1


----------

