Vacuum pump

[Frenchy]

Ok you mechanical minds, I know some of you work in refrigeration and small motors. Here is the time to show what you can do on a limited budget.

I am looking to build, buy a vacuum pump this should ideally have a chamber that is liquid tight. I was thinking of making the chamber out of an ammo can, then use rubber tubing to go up to the vacuum pump. The pump should generate at least 20” pressure but more is preferable.

The pump can not cause heat or sparks, as the product being vacuumed will be some what flammable.

Here is the application, In wood turning, there are many woods that are beautiful but full of holes or as in the case of burls, small voids that just explode when you turn them. I intend to make a tank that can hold 30” pressure (ammo can) and fill it ¾ with a stabilizer (Pentacryl) and suck the air out of the canister to force the Pentacryl into the wood. This would make it possible to then turn it like a laminated wood with out the fear of breaking the wood.

This material is used to dry and fill the wood with a plastic like substance, it is somewhat flammable, and so the fumes being vacuumed can not come on contact with heat or friction.

Any Ideas of inventors out there willing to make me some thing to work with?


I hear people use manual pumps and Refrigeration pumps to do this, but they do not say they use it to vacuum Pentacryl or a flamable solution.

This could be a self contained motor or a seperate pully type motor as i have a small motor I could use to atach to it. The unit should contain a guage to show the vacuum pressure also.

[normanvin]

if i understand you correct ly you wish to use the ammo box as a vac chamber. why not just use your ammo box/ vac chamber. then plumb a shop vac into the box.

that way you have a multi use vac. and you do not have to mess with pre filters for the vac pump. mc master carr sells an adjustable vac relief valve. the ammo can may collapse if you apply to much vac.

i may have a small vac pump in the basement i am not sure what it will draw down to.

i will check to see if i still have it.

[nijwnfi]

This is a workable pump, you could seal a gauge onto your chamber. http://www.harborfreight.com/cpi/cta...temnumber=3952 For your chamber, how about a pressure cooker? Check thrift stores or flea markets, you could probably find one cheap. As far as the gauge, you could also run it inline using barbed fittings.

[Dave D.]

Here is the application, In wood turning, there are many woods that are beautiful but full of holes or as in the case of burls, small voids that just explode when you turn them. I intend to make a tank that can hold 30” pressure (ammo can) and fill it ¾ with a stabilizer (Pentacryl) and suck the air out of the canister to force the Pentacryl into the wood. This would make it possible to then turn it like a laminated wood with out the fear of breaking the wood.

Frenchy, I think I understand what you're trying to do here; but I don't think the setup you've described is going to do much more than what you could achieve by simply dunking the wood in an open tank of Pentacryl and letting it soak in.

A vacuum would not actually "force" the Pentacryl into the wood; all it would do is suck the air out of the internal spaces within the wood, so that Pentacryl could flow in to replace it once atmospheric pressure is re-admitted to the chamber. And if the piece of wood is submerged in a pool of Pentacryl while you're drawing a vacuum over it, the air could only get out of the wood by bubbling out against the weight of the surrounding Pentacryl; so you probably wouldn't get very good evacuation of the air inside the wood, nor penetration by the Pentacryl. Also, like you say, the vacuum pump would have to be able to deal with the Pentacryl vapors in a way that would avoid a possible fire hazard.

I think there's a better way.

At the place I worked a few years back we had some assemblies (the guts for industrial pressure sensors, which we manufactured) with an internal cavity that had to be filled with silicone oil. The cavities were complex, with lots of little passageways and nooks and crannies, and they all had to be COMPLETELY filled with silicone with absolutely no air pockets whatsoever inside.

The setup we used involved two chambers, a vacuum pump, and three valves. Chamber A was the chamber containing our assemblies to be filled; it had a sealable access hatch that could be removed so you could reach inside. Chamber B was a reservoir that held the silicone oil. The two chambers were connected with Tygon tubing with a stopcock valve in between them. The vacuum pump was connected to chamber A with Tygon tube through another valve. And finally, chamber A had a port leading to the outside atmosphere through a third valve. Chamber B was mounted above chamber A, so that when the valve between them was opened, the silicone oil could flow down from B to A under force of gravity.

The drill was as follows: first, all valves were closed. Then the parts to be filled with silicone were placed in chamber A and the access hatch dogged down; chamber B was filled with silicone oil, enough of it so that when the oil drained down into chamber A it would completely cover the parts.

Then the vacuum pump was turned on and the valve connecting the vacuum pump to chamber A was opened. It took about an hour or so to pump down, IIRC, because we were drawing a pretty hard vacuum on these things so there would be absolutely NO air bubbles when we got done. Once we got the required vacuum, we turned off the pump and closed the valve.

Next, the valve between chamber B and chamber A was opened, allowing the silicone oil to flow down into chamber A and cover the parts. Since all the air had already been sucked out of all the little spaces inside the parts, the oil filled every nook and cranny like we wanted without having to apply any pressure.

After waiting a couple of minutes to make sure the oil had penetrated the parts completely, the valve connecting chambers A and B was closed and then the valve on chamber A's outside air port was opened. The access hatch was then opened, the parts taken out and sealed so the oil inside them couldn't leak back out, and the remaining oil poured back into chamber B for use on the next batch of parts. Rinse and repeat for each batch.

I suspect that's roughly the setup you'll have to use if you want the Pentacryl to thoroughly penetrate the wood-- or at least, penetrate any better than it would by simply dunking the wood in a tub of the stuff.

The one big difference in procedure that I can see is that once you've opened up the outside air valve on chamber A to let air back in, you're going to have to wait (certainly several minutes, possibly several hours and maybe even several days) while outside air pressure forces the Pentacryl through the fine pores in the wood all the way to the inside; I gather from Googling around that this "burl" stuff you're working with is pretty dense and doesn't absorb anything very fast. The way this page on woodweb.com talks about it, you could be in for a long wait.

Hope this helps a bit...

[RocketFoot]

If you do build a system, make sure you use a one way check valve with a bleeder on the vacuum line, otherwise the pump would have to work too hard to create the vacuum.

[Montanya]

Ok I got a crazy idea. Why not buy one of those vacu-saver bag systems. Bag up your wood and the solvent and then suck all the air out. Sounds like an easier way that going through a mass invention process.

[Atomic Dog]

If you do build a system, make sure you use a one way check valve with a bleeder on the vacuum line, otherwise the pump would have to work too hard to create the vacuum.

Yes.



I'm slightly ignorant when it comes to vacuum stuff, but wouldn't it be easier to use an existing small engine and attatch valves to the intake and exaust? You could power it with another motor easily and it should hold as much pressure as you need.


that or a giant piston...

[gnbrotz]

Ok I got a crazy idea. Why not buy one of those vacu-saver bag systems. Bag up your wood and the solvent and then suck all the air out. Sounds like an easier way that going through a mass invention process.

I'm not sure this would work well. I have a vacuum sealer and the instructions recommend to not vacuum seal items with a high liquid content (like soups) because the liquid will be drawn out of the bag (and into the motor) under vacuum before the bag is sealed. It recommends freezing these type of items first to eliminate the problem.

[IV_Warrior]

I like Dave D's response. I wonder if it would help, if after allowing the fluid into the chamber with the wood, if you then applied pressure to the chamber to help force the liquid into the wood. The air wouldn't get back into the wood as the wood would be submerged.

[Dave D.]

I like Dave D's response. I wonder if it would help, if after allowing the fluid into the chamber with the wood, if you then applied pressure to the chamber to help force the liquid into the wood. The air wouldn't get back into the wood as the wood would be submerged.

I didn't think of that; it would certainly help, the more pressure the better.