rotary vane pulling 28 inches??? Maybe???

[Rossell's Sugar Camp]

I was thinking the other day and got to wandering. If 2 rotary vane vacuum pumps were hooked up in series, would the vacuum capacity be increased enough to be considered high vacuum?

Vacuum pumps are rated at the change of vacuum. rotary vane pumps are around 15. In theory 2 pumps in series could possibly acheive high vacuum. Maybe not 28 but above 15 for sure!

Could the fact that not enough cfms of air would be moving through be a concern. Think about it. it has been driving me nuts!

[maple flats]

I think cooling would be the preventing issue. The rotary vane pump cools by both air flow around the pump body and internally by the air flow it is pumping. The latter is the greater amount of cooling, and with extremely high vacuum levels there is extremely little air to cool. That would overheat the pump and failure would soon follow. Some extra cooling method of the oil it needs might help, but that is true of even one pump. A problem there is that colder oil temperatures will slow the flow and starve the pump for the oil it needs.

[upsmapleman]

This may sound strange but hooking 2 in a series will not give you any more vacuum. I did it this year. A 7 1/2 hp Air Blo and a 5 hp Deavalve both flood oil. If I ran 1 or both, same vacuum. I talked to a local service man for diary and he said no, that vacuum is vacuum. you either have it or not. If you have some leaks 19" would be the most you could expect no matter how many pumps you put together. I know I was surprised. The 5 hp. was the same as if both were running.

[paul]

We have a 3hp Masport Major and always pulled 15" of vac and then we started putting water to the top of the head with a 5/16 line out of our permiate tank and started pulling 20". Then we stared putting oil into the intake side of the pump and stopped useing the water and now we can pull 24" of vac all season long with out any problems.so cooling is the key to those old dairy pumps.

[cray54]

If 2 rotary vane vacuum pumps were hooked up in series, would the vacuum capacity be increased enough to be considered high vacuum?

The way these rotary vane vacuum pumps are designed and built, each "batch" of gas that is drawn in to the pump is expanded and then separated from the intake before being connected to the exhaust. In an ideal example, nothing you could do downstream (to the outlet of the pump) would increase the vacuum upstream (at the inlet of the pump). There are leaks and losses that might lead to downstream changes having upstream effects, but minimally so.

-Chris

[Thad Blaisdell]

If you have the right rotary vane pump it is possible.

http://www.airtechusa.com/products/l-series-rotary-vane-pumps.html

[cray54]

If you have the right rotary vane pump it is possible.

It is definitely possible for high vacuum with a properly designed rotary vane pump... however, two single stage low-medium vacuum pumps in series will not function as a high-vacuum double stage pump.

[vernon]

What is TORR ?

[wiam]

What is TORR ?

It is a measure of vacuum. There is a conversion to inches of mercury.

[heus]

My Gast 3040 Rotary vane when deadheaded runs at 28+ but obviously in the real world thats not possible due to vac leaks, overheating, etc.

[Gary R]

My Gast finally runs 28" also. 1 TORR = 1 mmHg