vacuum pump ratings

[madmapler]

This may seem like a stupid question for some but, knowing that a gast rotary vane pump is rated for 28 maximum hgs. and the 21 cfms they list are free air hence a 28 hg pump is not close to that at the 21 cfms that its rated for, how is it for a sihi(for ex.)60cfm pump that is rated for 28hgs? In other words is the sihi rated in accord with the performance curve of that pump(28hgs at 60 cfms)? If it is then how do you determine how a pump is being rated? Often times I'll see a pump advertised and I simply guess according to the hp. of the pump. Thanks.

[GeneralStark]

There is no consistent method of rating vac. pumps that all manufacturers follow. Often they are rated at 15", but not always. The pump's performance curve is the only real close approximation of how the pump will perform at different vacuum levels. This topic has been discussed ad nauseum here. Read post #15 of this thread , which it looks like you were following, for specifics. The webinar included contains everything you would need to know about pump ratings.

http://mapletrader.com/community/showthread.php?20926-Max-taps-on-a-Gast-pump

[madmapler]

GS, Did you intend to provide a link to another thread? Thanks.

[GeneralStark]

I edited the post. Sorry about that.

[madmapler]

I cant seem to open that webinar page right now. I'll try again later. Thanks.

[unc23win]

If you are looking for information on Gast pumps try this e-mail. GBHTechnical@idexcorp.com Gast Technical support the dude Nick that answers back rocks he can answer questions as well as send you pdfs of the manual and such. When looking for pumps it helps to know how they are rated most Dairy pumps are rated at 15", but that doesn't mean they can't do more.

Last year I asked Carl Lapierre the same question again surprise Carl answers e-mail pretty fast as well. Below is his answer if you find out how the pump is rated you can use his formula to properly oversize the pump in question for you operation. I asked my question based on visiting the Lapierre sight and looking at used pumps for sale they give the ratings based on inches of vacuum so basically if you want 26" pick a pump that is oversized enough in CFMs to get you 26' for the number of taps you desire. I myself found a brand new GAST never used actually discontinued model asked Gast tech all about it then bought it.

Carl's Formula

Usually pumps are rated at 15 in/hg but some company rates their pump at acfm… (w/o any vacuum)

The formula to get approx cfm is quite simple, you take the rated ACFM of the pump lets go with 100 at no vacuum.

The you divide that 100 by 30 (should be 29.9) then you multiply the result by the difference of vacuum, if you want to know how much cfm is left at 20 in/hg, you substract 20 from 30, your left with 10, so (100 / 30) * (30 – 20) = 33.3 cfm

If the pump is really rated 100 cfm @ 15 in/Hg, it means its 200 acfm so again (200 /30) * (30 – 20) = 66.6 cfm

From there you just need to find out if it is rated at no vacuum or at 15 in/Hg

[madmapler]

Just saw your post unc23win, thanks.