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.
