DIY pressure chamber

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glycerine

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I'm sure this has been asked before, but have any of you guys built your own pressure/vacuum chamber? I found an article online where someone built a pressure chamber for vacuum infusing/stabilizing wood. It was made out of PVC and I've essentially done the same thing before building a potatoe gun. I've filled it to over 100 PSI, so I know it can handle the pressure, but it's also enclosed and sealed with the pvc glue. So I don't know if the threads will hold up as well or if there's something more to a pressure pot than just being a container that can hold a certain pressure...
Anyone have experience with this already?
 
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ldb2000

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Don't try it . This has come up before and the consensus has been it is verrrry dangerous . The PVC really isn't made for high pressures and eventually will self destruct ... catastrophically .
A pressure pot from Harbor Freight is still the safest way to pressure cast , and even they can go boom , just ask Jeff (workinforwood) who had a pot blow it's lid a couple of months back .
Here's the link to the thread http://www.penturners.org/forum/showthread.php?t=44180
 
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holmqer

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It would appear that PVC is rather susceptable to low cycle fatigue (LCF), and while it may be used for water pipes, I suspect that the pressure is not as high in water pipe as it is in compressed air applications so the LCF issues are reduced.

Typical municipal water supplies are designed to provide 40 to 70 PSI, and this pressure will fluctuate over over time with changing seasons and usage.

I am a bit puzzled why there are not more problems with PVC water pipe breaking. Between the pressure drop when a faucet is opened, and the water hammer effect when the faucet is closed there would appear to be a big pressure transient every time you use water, yet the pipes are not bursting left and right.

It would appear that PVC in water pipe use would be subject to similar max pressures and pressure cycles as PVC in compressed air systems, yet PVC in compressed air system seem much more susceptable to bursting.

I wonder if it is related to contaminants in the air? Perhapse instances of burst PVC in compressed air systems due to oil mist in the compressed air reacting with the PVC and creating a weakness. Regardless, I would not tempt fate and use PVC in compressed air applications. Perhapse someone will do a thorough study and come up with an explination, but until then I will avoid PVC.
 

stolicky

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Yes, PVC can become brittle over time and will generally fail catastrophically. I know the UV will weaken PVC over time. It will even weaken MDPE and HDPE plastic which is why there are safety regulations in the natural gas industry that limits its exposure to sunlight. Steel, on the other hand, could fail, but it is much less likely to shatter. Actually, I don't think I have seen any steel break into pieces except for when we dipped it into liquid nitrogen and whacked it with a hammer, back in college during materials class.

Plastics can be impacted by a laundry list of environmental conditions. Less 'plastic' plastics (material terminology) can develop micro cracks than can propagate suddenly when put under pressure.

Anyway, a steel pressure pot designed to hold pressure, is definitely the safest way to go. I read a couple of weeks ago in a thread about using PVC for air lines - 'Remember that x-rays do not pick up plastic.' If it shatters, you're screwed!
 

parnelli_97

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What if you're using the PVC as a negative pressure pot, vacuum? Even if it fails it will implode, possibly damaging the materials but not the user. The only reason I ask is I have a lot of PVC left over from some renovation work. And think, Acrylic with some embedded PVC could make some interesting turning material lol.
 
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glycerine

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Thanks for the advice. Would any of you feel differently about the strength of the PVC if it were wrapped with fiberglass, similar to some of the paintball tanks that you see nowadays?
 

jkeithrussell

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Get the HF pressure pot. It takes a little effort to get it set up properly, but it's no more effort that you're going to go through trying to make a pressure vessel out of a potato cannon -- and it will last longer and operate safer.
 

Daniel

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PVC is meant to handle pressure up to 60 P.S.I. At least the stuff generally off the shelf at the hardware store. Issues like water hammer are one that are very strictly regulated by the building department and are no longer allowed at all. Because pipes will break if they are allowed to happen. As for pressure changes. everyone knows what it is like to be in the shower when someone flushes the toilet, and even though there is a change in rate of flow. there is not that much of a change in the pressure in the pipes. This pressure is now sending the same amount of water out of the pipes, it is just now going out of two holes rather than one. Same pressure, same flow. more faucets to supply means less water per faucet.

In the case of using PVC as a pressure/ vacuum chamber. you are asking it to go from say 60 P.S.I. to a negative pressure of some degree. And as others have pointed out PVC cannot withstand these extremes.
 

RickW

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Typical municipal water supplies are designed to provide 40 to 70 PSI, and this pressure will fluctuate over over time with changing seasons and usage.

I am a bit puzzled why there are not more problems with PVC water pipe breaking. Between the pressure drop when a faucet is opened, and the water hammer effect when the faucet is closed there would appear to be a big pressure transient every time you use water, yet the pipes are not bursting left and right.

It would appear that PVC in water pipe use would be subject to similar max pressures and pressure cycles as PVC in compressed air systems, yet PVC in compressed air system seem much more susceptable to bursting.

I wonder if it is related to contaminants in the air? Perhapse instances of burst PVC in compressed air systems due to oil mist in the compressed air reacting with the PVC and creating a weakness. Regardless, I would not tempt fate and use PVC in compressed air applications. Perhapse someone will do a thorough study and come up with an explination, but until then I will avoid PVC.

Having been a water/sewer inspector for a few years in the Jacksonville area I can pass on what I remember.
Our water systems ran at a pressure of 70-80 psi. All water/pressurize sewer (force main) piping is required to be either ductile iron or HDPE DR 18 or 25. This pipe is thick walled compared to what you get at HD or Lowes which is normally SCH 40. The only SCH 40 we used was for 2" or under and mostly for water services. PVC pipe is normally just a slip fitting with a rubber seal to keep it from leaking. The reason it does not slip apart or explode is the pressure/friction of the earth/sand/dirt surrounding it, but at times it does explode. If there is a possibility of extra force from the inside of the pipe (such as sharp bends) then mechanicla joints/restraints are used to hold the pipe together. I had one job where we were installing 30" pipe with a 'T'. All pressure pipe has to pass pressure test prior to being put into service. Because this particular joint had given so much trouble it was decided to pressure test uncovered to see where it leaked if it did. Well, this joint exploded violently 2 times before it was decided to cover it and compact the dirt to help hold it in place. On the third try it held. Luckily no one was injured during these tests.
The reason turning on a faucet does not cause pressure drop is most of the mains (in Jax) are usually 20" or larger. And the pumps at the water plants are massive. A whole sub-division could turn on faucets and the water plant would hardly notice it.
Also, if I remember correctly, sunlight is not 'supposed' to cause PVC to deteriorate, but it will cause it to fade.
I would NOT use pvc pipe in pressure/vacuum situations. Explode/implode is the same thing. VERY sharp pieces of pvc flying everywhere.
 
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If you use hydraulic pressure it can only burst open with no danger to you, just a big mess.
On the other hand if you pump it up with air you would end up with a high volume of air inside the chamber and if it gives way under the pressure it would not burst open but it would explode. If you do use pvc try to install two pressure gauges and a relieve valve( adjustable) and be very vigilant when using the pressure chamber.

I would rather go with a Metal pressure pot.

I do stabilizing and have a chamber that can go up to 9000 PSi and even at that pressure it is save if it sprung a leak. It would only leak a cup of fluid. I also uses two gauges.

Good luck
 

glycerine

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If you use hydraulic pressure it can only burst open with no danger to you, just a big mess.
On the other hand if you pump it up with air you would end up with a high volume of air inside the chamber and if it gives way under the pressure it would not burst open but it would explode. If you do use pvc try to install two pressure gauges and a relieve valve( adjustable) and be very vigilant when using the pressure chamber.

I would rather go with a Metal pressure pot.

I do stabilizing and have a chamber that can go up to 9000 PSi and even at that pressure it is save if it sprung a leak. It would only leak a cup of fluid. I also uses two gauges.

Good luck

So, does hydraulic pressure basically compress the air that is already in the tank? If I bought a pressure pot, can I use either method or are they totally different?
 

glycerine

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PVC is fine for Vacuum. Just as glass is fine for vacuum. Remember, vacuum is not the inverse of pressure.

What's the difference in casting in a pressure chamber and a vacuum chamber? I know that vacuum is what is used when stabilizing, right. Why does everyone usually let their molds cure under pressure?
 

jkeithrussell

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What's the difference in casting in a pressure chamber and a vacuum chamber? I know that vacuum is what is used when stabilizing, right. Why does everyone usually let their molds cure under pressure?

Air pressure compresses the air that is inside the resin and keeps it compressed while the resin cures.

Vacuum is used in stabilization because it forces the stabilizing medium into the pores or cracks in the wood.
 

ldb2000

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What's the difference in casting in a pressure chamber and a vacuum chamber? I know that vacuum is what is used when stabilizing, right. Why does everyone usually let their molds cure under pressure?

The main reason for casting under pressure is that the higher pressure KEEPS the air in the resin in solution and don't allow bubbles to form . Think of a bottle of soda , with the cap on and the soda under pressure the CO2 is in solution with the soda and you see no bubbles . When you remove the cap and release the the pressure you see the bubbles form as the CO2 comes out of solution .
Pressure alone don't guarantee that you won't have bubbles in your blank , if there were bubbles created by mixing the resin and you put the resin under pressure you will still have the bubbles from mixing but no new bubbles will form
 
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Roy99664

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Yes I do use a pressure vessel made of schedule 80 Pvc. for casting. So far without problems.

Bursting rate for schedule 40 is 710 psi. Schedule 80 is 1100 psi.

7 to 10 times the pressure my compressor will produce.

Proceed at your own risk.
 

jleiwig

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Yes I do use a pressure vessel made of schedule 80 Pvc. for casting. So far without problems.

Bursting rate for schedule 40 is 710 psi. Schedule 80 is 1100 psi.

7 to 10 times the pressure my compressor will produce.

Proceed at your own risk.

Just thought I would bring this back from the dead to show what a manufacturer offers for a vacuum chamber. According to some guys on the taxidermy forums this combined with a robinaire 5 cfm vacuum pump will evacuate the chamber in less than 60 seconds.

12" dia. Sch 80 pipe with 2 1/2" pieces of lexan and a couple seals. They want 239 bucks for it. You could probably make it for $15 if you could find the offcut of pipe cheap enough.

attachment.php
 
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glycerine

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I just bought a 2.5 gallon Pressure Pot at lunchtime from Harbor Freight for $59 and it has regulators etc. Much easier than trying to build one!

I just like to build things. And sometimes I trust my own handywork over others. $59 is good, but that's on the cheaper end. Anywhere other than Harbor Freight, they'd be much more expensive.
Let us know when you use it how things turn out. I'm still trying to figure out if it's worth even using. I've had bubble free PR without pressure or even vibration, but I've heard pressure can make the PR stronger and denser...
 

glycerine

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Just thought I would bring this back from the dead to show what a manufacturer offers for a vacuum chamber. According to some guys on the taxidermy forums this combined with a robinaire 5 cfm vacuum pump will evacuate the chamber in less than 60 seconds.

12" dia. Sch 80 pipe with 2 1/2" pieces of lexan and a couple seals. They want 239 bucks for it. You could probably make it for $15 if you could find the offcut of pipe cheap enough.

Thanks for the info. By the way, I know nothing about taxidermy, what do they use this for?
 

GregHight

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I just like to build things. And sometimes I trust my own handywork over others. $59 is good, but that's on the cheaper end. Anywhere other than Harbor Freight, they'd be much more expensive.
Let us know when you use it how things turn out. I'm still trying to figure out if it's worth even using. I've had bubble free PR without pressure or even vibration, but I've heard pressure can make the PR stronger and denser...

I mainly got it because I've been wanting to use Alumilite.
 

ldb2000

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I just like to build things. And sometimes I trust my own handywork over others. $59 is good, but that's on the cheaper end. Anywhere other than Harbor Freight, they'd be much more expensive.
Let us know when you use it how things turn out. I'm still trying to figure out if it's worth even using. I've had bubble free PR without pressure or even vibration, but I've heard pressure can make the PR stronger and denser...

You still have to modify the pressure pot for our purposes . Pressure or vacuum is not NEEDED for casting in PR or Alumilite for that matter , it's CLEAR casting that are helped by either or both .
Pressure does not make the resin any stronger or denser , it just holds the air in suspension in the liquid resin until it cures .
 
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