Vacuum Table Pump Options

      A description of vacuum pump types and some advice on the limitations of cheap alternatives. June 26, 2006

I've been looking at the prices of ~20hp vacuums for holding material, and boy, they can get expensive. What would be the problem with using four shop vacs for a 4'X8' table? The shop vacs are 6.5hp, 210cfm, and pull 60" of water. Is this enough vacuum to pull through LDF or MDF and hold down material? Any other options for an affordable vacuum hold-down system (that pulls through MDF) for a small shop?

Forum Responses
(CNC Forum)
From contributor D:
Vacuum pumps that are used for bleed board systems typically pull 20 inches of mercury or better. 60 inches of water is less than 4.5 inches of mercury. Additionally, a shop vac is not going to run very long in a constant duty environment. I have seen shop vacs used to hold down large parts on a gasketed fixture, but I just do not think you are going to be successful with a bleed board.

From contributor B:
I tried a shop vac on a 12" x 24" bleedboard box. It worked okay for a 10" x 22" piece of panel stock, but not at all on a piece of poplar. That's a far cry from a 4x8 table.

From contributor G:
A shop vac can work well in a 2 x 4 area or more, but you have to be working with the right materials and setup. To make the advice short, forget about anything warped, anything too porous (I think MDF actually would be okay, but I'm not positive), and you have to tape off all areas not covered with material. Having said that, if the pieces are large enough (1 sqft plus), it will work pretty good.

I use a shop vac on one table of mine, a 49 x 39 Techno-Isel. I usually cut plastics and aim for full seal all the time (think onion skin at the bottom), but that is because I cut very small pieces (.5" x 1", etc.).

The shop vac will also hold up surprisingly well for years with crappy airflow (as it should be if your part is being held down). But, for the price of 4 shop vacs, and the issues above, I would think a regen blower would be better (more power on startup though) and quieter too!

All my experience with blowers (and a 10HP will outperform the 4 shop vacs, by the way) is with CNT Motion Systems. You might try calling them and seeing what the price would be.

From the original questioner:
That's one thing that confuses me... What's the difference between all the different kinds of pumps and blowers out there? There seem to be so many options. What exactly is a regenerative blower?

From contributor D:
A regenerative blower uses one or more rotating disks with air foils on the rim to generate either pressure or vacuum. Multiple disks in a multiple stage blower generate deeper vacuum than a single stage blower. The practical limit to vacuum with a regenerative blower is about 15 inches of mercury. This low cost, high volume system can work well with a bleed board system if your parts are relatively large.

Other systems include:
Lobe blowers (a little deeper vacuum than regenerative blowers, but higher cost, low maintenance and very durable. Can be loud.)
Vane pumps (quiet, deep vacuum, some maintenance of consumable vanes).
Liquid ring pumps (quiet, deep vacuum, low maintenance, not necessarily cheap, environmentally friendly water systems limited to about 15 hp, oil system up to 40 hp or so).
Screw pumps (loud, deep vacuum, can be enormous, most likely choice for large systems).

From contributor B:
Good descriptions. I'll only add the deep vacuum pumps in the rotary vane category (typically 15" to 26" of mercury depending upon the pump) are low air volume. They are good for gasketed fixtures and pods but not for through (bleed board) vacuum setups. I refer to these as true vacuum pumps.

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