# Pressure Vs. Vacuum



## TurtleTom (Oct 31, 2015)

I'm been reading the posts, honest.  Searches don't seem to help much.  I'm sure I'm missing something senior here. 
Why do some pressurize blanks and some vacuum blanks?


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## ElMostro (Oct 31, 2015)

Generally the norm is pressure for casting and vacuum for stabilizing.  BUT, depending on how weird your project is you may use either for both.

When casting (especially with urethane resin) using vacuum introduces bubbles that will likely remain once the resin is set so vac is not generally helpful.

When stabilizing you generally start with vacuum and SOME folks like to use pressure after vacuum to speed up the saturation process.  Then others start with pressure then vacuum then pressure again....so it depends on the type of wood and what you are doing.  I like to extract the air dry then once the air is out slowly introduce the dye/stabilizing solution while still under vacuum...you can't see a whole lot of bubbles this way but then again I am not entertained by watching bubbles.  Confused yet?
Eugene.


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## TurtleTom (Oct 31, 2015)

I would think your method of wetting under vacuum would be most efficient, especially if followed by pressure.  
I would think drilling a hole through the center would double the effectiveness since it no longer has to go all the way through the blank.
Thanks for the reply.  I need to build a chamber to do all that, oilfield style.


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## larrystephens (Oct 31, 2015)

*Look at Turntex*



TurtleTom said:


> I would think your method of wetting under vacuum would be most efficient, especially if followed by pressure.
> I would think drilling a hole through the center would double the effectiveness since it no longer has to go all the way through the blank.
> Thanks for the reply.  I need to build a chamber to do all that, oilfield style.



Rather than reinvent the wheel look at what Curtis does at Turntex, his chambers are the best.


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## jttheclockman (Oct 31, 2015)

Many past threads on this topic.

http://www.penturners.org/forum/f43/pressure-pot-vs-vacuum-71081/


http://www.penturners.org/forum/sea...o=1&photoplog_searchquery=pressure+vs+vaccuum


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## TurtleTom (Oct 31, 2015)

Turntex has some nice equipment, but sad to say, it's much cheaper reinventing the wheel.  Anyway, it's a shame letting all that oilfield welding experience go to waste.


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## low_48 (Oct 31, 2015)

TurtleTom said:


> I'm been reading the posts, honest.  Searches don't seem to help much.  I'm sure I'm missing something senior here.
> Why do some pressurize blanks and some vacuum blanks?



You're posting in the finishing section. Are you asking about casting urethane, polyester resin, stabilizing, finishing? I'm confused about what you are asking about.


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## Skie_M (Oct 31, 2015)

Heh ... yeah, it does look like Tom posted in the wrong forum. 


I would say, if you want to stabilize ... the best method would be to set your chamber up with some heavy magnets on the outside and a steel insert on the inside that will ride the magnetic field while it's in use ...  set it so that your blanks are floating on the steel insert above your stabilizing fluid.  (Make it a basket, so you get fuller use of your stabilizer.)

Set up the vacuum pump first, and pump the air out of the chamber.  Lower your magnets to make the steel insert basket drop into the stabilizer and then release the vacuum.

If you wish, at this time, you can then (double check the lid to make sure it's sealed) pressurize the pot to force additional stabilizer into the blanks.


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## MesquiteMan (Nov 1, 2015)

Stabilizing is all about displacing the air in the wood with resin.  In  order to fill the wood, you have to get the air out.  An analogy I use  when I teach classes is take a cup and turn it upside down and push it  under the water.  As long as there is air in the cup, the cup can never  fill up with water.  Remove that air by tipping the cup over and the cup  will now be filled with water.  Vacuum is removing the air in the wood  but NOT getting resin into the wood.  It is when you release the vacuum  that resin begins to go back into the wood.

For dry vac vs wet vac (vac pulled on wood, then resin introduced vs. wood submerged in the resin) there is no difference in end results or wear on your pump.  The pump is creating a  lower pressure in the air space in the chamber, be it above the resin  in a wet vac setting or in the entire chamber in a dry vac setting.  The  pressure deferential is what causes the air to flow from the wood since  the surrounding pressure is lower than the internal pressure in the  wood.  Nature does not like to be out of balance, thus the flow or air  from a higher pressure to a lower pressure.  The resin has no effect  whatsoever on the process.  The only benefit of doing a dry vac is you  do not have as much foaming for the first 5 minutes of the operation.   Of course this foaming is easily controlled by valves.  The downside of  doing the dry vac is the extra valves, hoses, and places for things to leak.  I prefer simple.  Dry vac complicates the process  more than is needed, IMO.  The end results will not be any better with  one vs. the other but wet vac is simpler.  Fill chamber, hold wood down,  add resin, vac until bubbles stop.  Release vac and allow to soak.   Done!

Some folks think that pulling a dry vac will make it so the pump does not work as hard since they think the air coming out of the wood is being sucked through the resin.  Again, it is not being sucked through, it is moving on its own and the vacuum pump is only affecting the air space above the resin.  

I am the type that likes to have data to back things up so I did some  testing a while back.  One way to determine how much  work an electric motor is doing is by measuring amp draw.  I got out my  amp clamp and did a little testing.  Here are the results:

This test was done with a JB Eliminator DV 6-E vacuum pump and a 4" x  10" vacuum chamber.  The same exact chamber and hose set up was used for all testing.  Here are the amp readings:

5.9-6.0 amps - No hose attached to the pump, open port
6.0-6.1 amps - Hose attached to the pump and chamber with valve open on the chamber, nothing inside
5.6-5.7 amps - Vac chamber at full vacuum, nothing inside-15 minutes in
5.8-5.9 amps - Full vac with a piece of buckeye burl 1 3/4" x 2 1/4" x 5 1/2", dry vac, no resin-15 minutes in
5.7-5.8 amps - Full vac with piece of buckeye burl 1 3/4" x 2 1/4" x 5 1/2", wet vac after foaming under control, 15 minutes in

The amp meter was fluctuating between the two readings a little so I gave both.

This shows that wet vs dry, there  is not much statistical difference in the amount of work the pump has to  do.  In other words, the pump is not working harder with either one.   The pump is actually working the hardest when it is moving a lot free  air.

Adding pressure afterwards does not increase the amount of resin you get into the wood in almost all cases.  You can accomplish the same thing by just letting the blanks soak at atmospheric pressure submerged in resin for the proper amount of time after releasing the vacuum.  The only thing pressure does is speed it up some.  I never understood the reasoning that some think using pressure, then vacuum, then pressure again is going to be better.  Sure, pressure will force the resin into the wood by compressing the air in the wood.  However, as soon as you release the pressure, the air in the wood expands and pushes the resin right back out.  The initial pressure is simply wasting time.


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## MesquiteMan (Nov 1, 2015)

TurtleTom said:


> I would think drilling a hole through the center would double the effectiveness since it no longer has to go all the way through the blank.



Drilling the hole will not make a difference if the blank is long grain.  The air flows from the wood predominantly along the grain rather than across the grain.  When you watch blanks submerged in resin, the vast majority of the air is coming out the ends of the blank.  Then, once you release vacuum, the resin flows back into the wood via the same pathway the air came out.  Predrilling does not affect the penetration of the resin.  If you want to reduce the amount of time you pull vacuum, then reduce the length of the grain.  You can go ahead and cut your blanks close to size and it will reduce the length the air has to travel and thus reduce the amount of time you pull vacuum and then the amount of time you have to allow the blanks to soak.

Also, pull vacuum until the air stops coming from the wood and you can do any size piece you want to do and get complete penetration and saturation.  I once did a 8"x8"x4" thick piece of hackberry with dyed Cactus Juice.  When I turned a bowl from it, I had complete, even color all the way through the blank and not one spot in it that was not properly stabilized.  I have customers who do walking stick blanks and pool cue blanks MUCH longer than any pen blank and they get consistent, fully stabilized blanks.


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## TurtleTom (Nov 1, 2015)

Who would thing "pot" would be necessary for the search.  Reason would insist that "Pressure vs Vacuum" would be sufficient or anything remotely academic.  But no...
Turntex's videos are down, for my computer anyway.  
How hard can it be?  The release of liquid while maintaining a vacuum is going to be a little tricky.


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## Skie_M (Nov 1, 2015)

Why not figure a way to do it like I described?  Use magnets to hang a stainless steel basket in your vacuum pot... drop the pressure to pull the excess air out of the wood while it's dry (and you won't get so much bubbles and foam) and then lower the basket into the stabilizer while it's still under vacuum by moving the magnets down.  

Wait till there are no more bubbles coming from the wood, and then release the vacuum seal and let it soak a bit.


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## TurtleTom (Nov 1, 2015)

Skie_M said:


> Why not figure a way to do it like I described?  Use magnets to hang a stainless steel basket in your vacuum pot... drop the pressure to pull the excess air out of the wood while it's dry (and you won't get so much bubbles and foam) and then lower the basket into the stabilizer while it's still under vacuum by moving the magnets down.
> 
> Wait till there are no more bubbles coming from the wood, and then release the vacuum seal and let it soak a bit.



That's a great idea Skie.  I'll try that first.


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## MesquiteMan (Nov 1, 2015)

Why complicate things?


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## TurtleTom (Nov 1, 2015)

MesquiteMan said:


> Why complicate things?



Explanation please.


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## MesquiteMan (Nov 1, 2015)

Please see my lengthy post above about dry vs. wet vacuum.  The initial foaming lasts about 5 minutes when doing wet vacuum.  You control the foam with a valve open to the atmosphere.  Once you are at full vacuum, walk away and let it do its thing for a few hours.  Once the bubbles stop, release vacuum and allow to soak.


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## MesquiteMan (Nov 1, 2015)

Oh and I just checked my videos and they are all working on my end.  They are all Youtube videos so even if they were down, it would be on Youtube's end.


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## Chromey (Nov 1, 2015)

Also don't forget water boils under a vacuum so therefore, helps in drying process of wood for stabilization.


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## TurtleTom (Nov 1, 2015)

MesquiteMan said:


> Oh and I just checked my videos and they are all working on my end.  They are all Youtube videos so even if they were down, it would be on Youtube's end.



I had already seen all of your videos, which are extremely well done.  
I'm understanding you to say it doesn't make any difference if you lower the blanks into an already vacuumed liquid or start submerged since the foaming is going to go away and not be a problem.  

I love the design and engineering of all your products, definitely top shelf stuff you make.


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## TurtleTom (Nov 1, 2015)

Chromey said:


> Also don't forget water boils under a vacuum so therefore, helps in drying process of wood for stabilization.



Is this a suggestion to vacuum the blanks before stabilizing?


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## MesquiteMan (Nov 1, 2015)

Using vacuum to remove water from the wood can be done but it takes about 30 hours of constant running of the pump to do so.  You will also most likely have to stop part way through and change the oil since the water that is boiling out of the wood will condense in the oil and it will become over filled.  You are also more likely to gum up your pump since you will likely be boiling sap elements with the water.  The best practice is to dry the wood in an oven at 220° F for 25 hours prior to stabilizing.  Also, the water will boil out of the wood whether the blanks are submerged or dry just the same so no, this is not a benefit of doing a dry vac.


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## MesquiteMan (Nov 1, 2015)

TurtleTom said:


> I'm understanding you to say it doesn't make any difference if you lower the blanks into an already vacuumed liquid or start submerged since the foaming is going to go away and not be a problem.



That is correct.  There is no difference in the finished product whatsoever or the time it takes to do it.  With one you have 5 or so minutes of attending it to control foam and then walk away.  With the other, you start the vac and let it run for a while, then come back and introduce the resin, making sure it does not splash up and get sucked into the pump.  Then you walk away.  The pump does not work harder in either case.


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## TurtleTom (Nov 1, 2015)

I really appreciate you time and consideration, Curtis.  I'll probably pay back buying some of your Cactus Juice soon as I'm ready.  Now I know how to do it anyway.....maybe. 

Thomas Hanson


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## low_48 (Nov 1, 2015)

MesquiteMan said:


> Using vacuum to remove water from the wood can be done but it takes about 30 hours of constant running of the pump to do so.  You will also most likely have to stop part way through and change the oil since the water that is boiling out of the wood will condense in the oil and it will become over filled.  You are also more likely to gum up your pump since you will likely be boiling sap elements with the water.  The best practice is to dry the wood in an oven at 220° F for 25 hours prior to stabilizing.  Also, the water will boil out of the wood whether the blanks are submerged or dry just the same so no, this is not a benefit of doing a dry vac.



And don't forget acids in the wet wood. Something like white oak is very acidic and can even rust out a kiln. Can't be good for a pump!


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## ElMostro (Nov 1, 2015)

TurtleTom said:


> MesquiteMan said:
> 
> 
> > Oh and I just checked my videos and they are all working on my end.  They are all Youtube videos so even if they were down, it would be on Youtube's end.
> ...



I guess I should have added that if all you are doing is some "willy nilly" stabilizing then dry vacuuming is overkill but if you are doing some more "complicated" work then it helps make things things come out how you want them.


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## MesquiteMan (Nov 1, 2015)

low_48 said:


> And don't forget acids in the wet wood. Something like white oak is very acidic and can even rust out a kiln. Can't be good for a pump!



HVAC systems have lots of acids from the flux they solder everything together with too.  That is why oil filled rotary vane pump manufacturers say to change the oil after every use.  For stabilizing, if you start out with dry wood as I recommend, the oil does not need to be changed after every use since there will not be anything in the chamber to boil off.


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