There is a wide discrepancy between the levels of vacuum that different types 
of vacuum pumps and blowers can generate.  Some kinds are rotary screw pumps, 
liquid ring pumps, rotary vane pumps, positive displacement blowers like a 
roots blower, or regenerative blowers (which are more like a fan).  You need to 
consider both the level of vacuum you need to attain and the amount of air you 
need to move to get there.  Compare a 10HP regen blower, vs a 10HP rotary vane 
pump.  The regen blower can move 4 times as much air as the positive 
displacement vane pump.  But the vain pump can draw more than twice the vacuum 
level.  Which would hold a part better will depend a lot on table design and 
area.  An open hole table with small pockets over the holes can work very well 
with the blower, but the blower will struggle trying to hold small parts on a 
fall board.  The vane pump would work great on closed pods and jigs or a 
smaller fall board, but if the table is very large or an open flow design it 
won't be able to keep up and vacuum levels could fall too low.

A 5ft x 10ft fall board (sheet of MDF that has been skinned can flow nearly 
300acfm (maybe a bit more) of air when a 15inHg vaccum is applied to it.  But 
if you need 20inHg to hold your parts, you're going to need a much larger and 
more powerful pump to get there (probably at least double).  But if you only 
need 10inHG the flow through the board will be much less probably closer to 
100ACFM.  The greater the pressure differential the higher the flow and 
leakage.  This is why gasketed jigs and pods work so much better for holding 
pieces.  You don't have the flow to contend with, you only need a pump capable 
of generating the pressure level you need and the ACFMs of the pump are less 
important.

Todd Zuercher
P. Graham Dunn Inc.
630 Henry Street 
Dalton, Ohio 44618
Phone:  (330)828-2105ext. 2031

-----Original Message-----
From: Les Newell <les.new...@fastmail.co.uk> 
Sent: Wednesday, June 09, 2021 2:42 PM
To: emc-users@lists.sourceforge.net
Subject: Re: [Emc-users] OT: About a chat here on vacuum table ideas

[EXTERNAL EMAIL] Be sure links are safe.

I tested a 1.5kW vacuum cleaner motor for this application a while back and 
wasn't impressed. They don't generate enough vacuum in my opinion.
You really need vane pumps or side channel blowers. Vane pumps generate a very 
strong vacuum but use a lot of power. Side channel blowers generate more flow 
for the same power but less vacuum. I used to operate a machine with a  1.2m x 
2.4 bed that had two 2kW side channel blowers and the vacuum was marginal. I 
did have parts move occasionally.

Les

On 09/06/2021 16:31, Roland Jollivet wrote:
> A friend was complaining about the need for 6kW vacuum system on a 
> large table and this got me thinking....
>
> Another way is to divide the table up into squares, grid wise, and 
> have a .. separate.. vacuum motor for each section. The motor is 
> mounted under the table at the bottom of each 'box'.
> You can get ~1.5kW motors really cheap, and now it's easy to make up a 
> system with as many kW as you want.
>
> Far easier to find 4 vacuum motors than a 6kW pump.
>
> Roland
>



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