Vacuum Table - piping

[tri4sale]

I'm working on setting up a vacuum table on my PRS 48x96 and have been reading up, but one thing I've not seen (may have missed it) is the size of piping to use under the table. 4" seems really big to use, so is 3" or 2" better to use?

[Brady Watson]

3" for the manifold. 2" for everything else.

Loud pipes save lives...

-B

[Simops]

Brady, does it have to be 3" for the manifold? Can you get away with having everything 2"??

Cheers

[bleeth]

I first used 1 1/2" and it worked but the improvement when I changed all to 2" was dramatic. My blower has a 2" inlet and outlet. The all 2" has worked for me, but, for all I know, if I increased the volume of air in the pipe more with 3" lead in and manifold it might improve even more. My blower is 16' from my table so there is a pretty substantial volume involved.

[Brady Watson]

Brady, does it have to be 3" for the manifold? Can you get away with having everything 2"??

'get away with'...yes - but at the cost of airflow due to pump cavitation unless you are running a low CFM pump. If you have something that moves a decent amount of air, (Let's say over 150 CFM), then you should have the larger pipe on the manifold. The larger diameter of the 3" makes up for all of those bends & tee's that restrict flow.

If you pop the hood of your car/truck, and take a look at the intake manifold, you'll see that there is a large breadbox intake with smaller runners coming off of it. Same idea here. The form factor of the 3" also plays well with the SB frame (on gantry tools anyway) since you can run 2 hose clamps around it and the lower 3x5 crossmember to secure it pretty well. If only using 2", you'd have to come up with your own idea.

On a BT tool, 2" should be fine as there really isn't that much surface area to deal with anyway, unless you are running a long powerstick. 2 smaller vac sources, like Lighthouse et al, would be fine running 2" underneath with a longer stick. Stock 32 or 48" tables are fine with one vac source. I had good results running 1x3x1/8" wall AL rect tubing underneath to clear all the rollers + some plumbing parts (P-trap etc) on my BT48. It worked very well.

-B

[tri4sale]

Does it make a difference if you are using Fein vacs as the vacuum?

[Brady Watson]

If using a Turbo I or II with the small dia hose, probably not too much. The Turbo III uses a 2" (2.27" OD) hose & necking it down definitely does restrict airflow.

-B

[ntraub01]

Question...

I completely understand that the volume of air moved is significantly dependent upon the diameter of the piping used to move said volume of air...BUT, in a vacuum table isn't the volume of air constantly decreasing because of the fact that we are trying to establish a vacuum???

Ultimately, if we are able to establish a 100% vacuum within our system there won't be any air movement. I also know that in reality establishing a complete vacuum is very difficult and nearly impossible to maintain because the materials we typically use are porous and will allow some air into the system which will need to be evacuated to maintain the vacuum.

With that being said, yes we need to use piping of some significance just so we can easily evacuate the existing air and establish the initial vacuum. I used 2" schedule 40 PVC throughout the system and it takes no more than 2 seconds to pull a vacuum that is adequate to hold a 6"x6" piece of material. Honestly, doesn't the size of the piping depend upon how much "cut though" one is typically going to experience while milling a sheet of material? If you are going to make a significant number of smaller pieces I would guess you would need larger piping to handle the additional air entering the system.

We can also minimize the amount of air entering the vacuum system by using downcut spiral bits to help close the "cut through".

Another thing that is very important is to engineer a way to completely bypass the plenum and open the system so the motors can breath freely and cool themselves. My cut cycles typically range from 10-30 minutes each and if I don't allow my motors to breath freely between cycles they will become heat soaked and quickly reach their point of failure. I do have a relief valve plumbed into the systems to help cool the motors while they are under load, but that volume is not adequate to shed the built up heat between cut cycles.

Just by 50 cents worth!

Nicholas

[Simops]

Brady, I'm looking seriously at a 2200watt 240VAC single phase 3hp Regen blower (my power availability to the shop dictates). I only want to hook vac to my 48" x 48" buddy table to better cut al. So a penny for your thoughts on tubing size?

Also just want to clarify......when you say manifold, that's not referring to the flange that goes into the table....right? It's something additional (got a photo of one?).......in fact do I need a manifold at all?

Cheers

[Brady Watson]

Marc,
CFM is inversely proportional to suction (Hg") as the pump operates. The pump moves the most air at 0 Hg" and the least (ideally 0 CFM) at max Hg". You want to make sure that your pump can run in free-air through your plumbing with the minimal of restriction or you be building vacuum with NOTHING on the table due to restriction and or friction in the tubes before the air gets to the pump. When in doubt, go bigger. This is especially true on low CFM pumps where people use 1/8" spaghetti tubing that totally chokes airflow & prevents the pump from ever creating a good seal to pull the part down & 'get over the hump'. It is a simple matter of displacement.

Mike,
You only need a manifold if you plan on distributing the vacuum to multiple zones. Gate or ball valves are typically part of a vacuum manifold...just like your intake manifold on your car with each runner going to an individual cylinder & intake valve.

I have no idea how to advise you on your plumbing and pump from the data you provided. Please chime in with rated airflow and max suction rating - or a 'pump map' (like a turbo) - as these are the only meaningful numbers to figure out what you need & what you'll get.

-B