Calculating flowrate on a vacuum line

[fortycoats]

Hi All,

We have a vacuum packing process where we need to draw vacuum down to 120mbar. The vacuum pump used for this is an 11kw oil lubricated rotary vane pump. The delivery line to the machine is 3" vacuum pipe.

If we were to install more machines it would be great if we were able to spec the pump based on the 120mbar required. I need to calculate what the flow rate would be for this process. What information is needed to workout the flowrate to correctly spec the required pump speed?

Thanks in advance

 

[BigInch]

What's the initial volume V0, and the reduced volume V1 of the package and how long do you want to take to shrink it?

Take V1-V0 and divide by the time. That's the flowrate you want. Now just find a pump that will do that flowrate with a low suction pressure of 120 mb.

That is that 120 mb absolute pressure, right?


If you were plowing a field, which would you rather use? Two strong oxen or 1024 chickens?" - Seymour Cray (1925-1996), father of supercomputing
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[fortycoats]

Biginch. Thanks for your help. The volume is the tricky part. Its like a pack of vacuum sealed bacon! our product is put into an empty pouch and a top layer of film then applied. So I am not sure how to go about calculating the volume accuratley

 

[BigInch]

Me neither. Maybe you could assume applying the plastic wrap traps a 1/2" of air above the bacon, or something like that.

If you were plowing a field, which would you rather use? Two strong oxen or 1024 chickens?" - Seymour Cray (1925-1996), father of supercomputing
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http://virtualpipeline.spaces.live.com/

 

[zdas04]

How accurate do you need to be for compressor sizing? Could you calculate a volume based on the average size of the film sheets and the average thickness of the bacon, then subtract the average volume of the bacon slab?

David

 

[BigInch]

Actually I'd think you'd want to evacuate the package by creating a vacuum in the drawdown line by flowing past its outlet. Then just let Bernoulli do his thing.

If you were plowing a field, which would you rather use? Two strong oxen or 1024 chickens?" - Seymour Cray (1925-1996), father of supercomputing
***************

http://virtualpipeline.spaces.live.com/

 

[KiwiFriggy]

In the interests of maintaining stable vaccum irrespective of reasonable demand variations, you may want to consider utilising a 4 - 20 mA pressture transducer and variable speed drive system.

 

[BigInch]

Lots of cycling of that VFD won't do it or the motor much good at all, especially when you need the most torque and least flowrate when you're drawing out the last tiny bit of air!

"Make everything as simple as possible, but not simpler." - Albert Einstein (1879-1955)
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[KiwiFriggy]

I agree in respect to keeping things as simple as possible. However if there is a derivable benefit from achieving constant vaccum across a range of various capacity levels, it is worth considering. In a number of countries there's plenty of this going on in the Dairy Industry, (on farm). I suggest some informed consideration be given to utlising the techology. It has to be said that generally there is reluctance to employing this kind of technology on vacuum systems, usually through inexperience.

 

[BigInch]

Its possible, but the OP does not suggest that appropriate conditions exist to employ VFD. I don't see where discussing it any further here is benefiting anyone.

"Make everything as simple as possible, but not simpler." - Albert Einstein (1879-1955)
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http://virtualpipeline.spaces.live.com/

 

[KiwiFriggy]

I suspect you are actually correct in your assertion, contrary to the fact that the application seems very similar to one I'm familiar with where several thousand systems are currently being employed successfully. (Ironically mostly using 11 kw motors with 3 in. suction lines)

 

[BigInch]

I agreed it was possible and, if the OP gave more data, alternatives could be properly evaluated on total merit. Until then, we could speculate on an infinite number of possibilities; a study I don't have the necessary economic incentives to complete. I yield the floor to those that do.

"Make everything as simple as possible, but not simpler." - Albert Einstein (1879-1955)
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http://virtualpipeline.spaces.live.com/

 

[katmar]

It is sad when a thread like this develops to a point where it could actually become interesting and a beneficial learning exercise to all involved, but the OP simply disappears and never provides the requested information. It seems to be happening more and more often, or maybe I am just becoming more grumpy as I get older.

Katmar Software
Engineering & Risk Analysis Software

http://katmarsoftware.com

 

[Artisi]

katmar, I agree re the original posters disappearing - a bit more feed-back where possible a thank you would be nice (sometimes).
I'm gettting older but not sure about getting grumpier - hopefully more understanding of the inconsiderate #-) around.

 

[BigInch]

Could be they just don't care to be force feed a VFD discussion.

"Make everything as simple as possible, but not simpler." - Albert Einstein (1879-1955)
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http://virtualpipeline.spaces.live.com/

 

[katmar]

Nah, OP hasn't logged on since September 29.

Katmar Software
Engineering & Risk Analysis Software

http://katmarsoftware.com

 

[fortycoats]

Hi All,

Just back from holidays so sorry for not responding sooner. I have being occupied with other issues and havent had much time to concentrate on this one. Next week i will be starting back into this area so i may need help later!

Regards