CNC Vacuum Pump Sizing and Elevation

Altitude affects the efficacy of a vacuum pump for CNC hold-down applications. Here's some info on how to make the adjustment. May 16, 2005

I am at 2700' elevation and am looking at CNC 25 hp Vacuum combo. I will be using it for NBM. Is it enough? I know that a 40 hp would be ideal, but that seems like it would suck a lot of juice. I would have the option of adding an additional 10-25 hp if needed. I’m wondering what some of your thoughts are.

Forum Responses
(CNC Forum)
From contributor A:
I had a customer in Colorado who insisted on us using a Dekker pump for their CNC machine installation. They said it was the only vacuum that would give them the power they needed at their elevation.

From contributor B:
I agree the Dekker is a great pump that you will not regret buying. The 25 hp should work but you will never worry with a 40 hp.

From contributor C:
The size of the vacuum pump needed depends on your table size. I would not run a 25 hp pump on a 5' x 12' table but would on a 4' x 8' table. Another note - vacuum pumps are not like air compressors. They demand less and are much more efficient, especially under full vacuum.

From contributor D:
The use of a vacuum pump at altitude requires that you consider the vacuum clamping force needed to hold the parts to be cut in place while you are cutting. There is less vacuum force available at altitude because there is less air trying to get into the space you are sucking into with your vacuum pump. The motor driving a vacuum pump doesn't work as hard at altitude because there is less air to remove while running at altitude at the same speed as on the ground at sea level. Electric motors are designed to run at a set speed and will run at that speed regardless of what the air pressure is: but the pump will produce less vacuum at an altitude. And of course the horse power requirement will be less. To get more clamping force at altitude you will need a bigger pump but can drive it with a smaller horse power motor.

From contributor E:
In theory, you lose one inch of vacuum per one thousand feet of elevation. At 2700' you are limiting the vacuum read on inexpensive gauges to 2.7" Hg less than stated on manufacturer’s data.

In actuality, the vacuum pump is creating specified vacuum based on its curve. If you put an absolute gauge on the pump, a gauge that is not affected by atmospheric conditions, you will see the pump doing stated performance.

Liquid ring vacuum pumps are the most forgiving and quietest vacuum pumps on the market. As long as you maintain a water temperature in to the pump suitable to the degree of vacuum you wish to achieve, water sealed units are great. They can be oil sealed and achieve a higher degree of vacuum.

Rotary screw and rotary lobe vacuum pumps are noisier and require sound deadening enclosures. Each has an extremely tight tolerance internally and do not accept foreign debris very well.

My credentials are over 30 years selling vacuum pumps to most all industries. I no longer am in the vacuum industry but like to help whenever I can.