The Sience of Suction

JPG · Post by **JPG** » Thu Apr 30, 2009 2:42 am

mickyd wrote:From the blackboard
http://www.shopsmithacademy.com/SS_Arch ... ection.pdf

HOKAY! I missed the scroll bar.

Thanks!:)

charlese · Post by **charlese** » Thu Apr 30, 2009 2:48 am

Mark - Thanks for asking the question!!:D We all learn and get refreshed! Some of this stuff we need to see several times.

JPG · Post by **JPG** » Thu Apr 30, 2009 3:03 am

charlese wrote:Mark - Thanks for asking the question!!:D We all learn and get refreshed! Some of this stuff we need to see several times.

Especially those of us who 'forget' often!:D

guitarnut · Post by **guitarnut** » Thu Apr 30, 2009 10:50 am

Good morning all. Thanks so much for the kind welcome to the forum. Already I feel a spirit here that exists in very few online communities.

So, I guess there is a similarity to water, except that instead of a pressure increase, restrict the air flow and the velocity increases.

I just watched the video and did the quick numbers. They are approximate because the charts in the pdf only show SPdrop up to 4500 fpm and it doesn't show 2.5" hose.

SS DC3300 @ 330 CFM thru 2.5" hose would produce a velocity of just over 9700 fpm. At the end of a 12' run of hose, the SPdrop would be appox 1.25. It's not clear in the video why he wanted the number to be below the lowest SP rating. I would think to derive the SP of the completed system, you would want to subtract your SPdrop from 7...the highest system rating with no hoses attached. In my case it would be 5.75. As others have said, more than enough for the single operations of the Mark V.

It's great to be a part of the forum and thanks again to all who added to the discussion...anytime I can use pizza as part of a math lesson, I'm for it! If I did the math correctly, each 12oz Miller Lite is 28.22 cu in of golden goodness!

Peace,
Mark
SW Indiana

JPG · Post by **JPG** » Thu Apr 30, 2009 11:14 am

guitarnut wrote:Good morning all. Thanks so much for the kind welcome to the forum. Already I feel a spirit here that exists in very few online communities.

So, I guess there is a similarity to water, except that instead of a pressure increase, restrict the air flow and the velocity increases.

I just watched the video and did the quick numbers. They are approximate because the charts in the pdf only show SPdrop up to 4500 fpm and it doesn't show 2.5" hose.

SS DC3300 @ 330 CFM thru 2.5" hose would produce a velocity of just over 9700 fpm. At the end of a 12' run of hose, the SPdrop would be appox 1.25. It's not clear in the video why he wanted the number to be below the lowest SP rating. I would think to derive the SP of the completed system, you would want to subtract your SPdrop from 7...the highest system rating with no hoses attached. In my case it would be 5.75. As others have said, more than enough for the single operations of the Mark V.

It's great to be a part of the forum and thanks again to all who added to the discussion...anytime I can use pizza as part of a math lesson, I'm for it! If I did the math correctly, each 12oz Miller Lite is 28.22 cu in of golden goodness!

By keeping the system total below the system rating, when you DO the subtraction, the result is POSITIVE. If the result is negative. your system is too restrictive and CF/M and velocity will decline below minimum required.
Peace,
Mark
SW Indiana

Use the 2" values for 2.5" hose(ERRS ON THE SAFE SIDE).

Air is a fluid just like water and restricting flow(as through a nozzle) increases the velocity in both cases. The pressure does not increase. The static pressure decreases.

"Pressure" washers depend on the increase in velocity of the water and the inertia of the fast moving water to do it's work.

2manband · Post by **2manband** » Thu Apr 30, 2009 1:28 pm

It's a complex issue - in any fluid moving through a pipe (or duct, or what have you) there will be a relationship among velocity, length of the conduit, diameter or cross sectional area of the conduit, flow velocity, volumentric flow rate (CFM), static pressure, dynamic pressure, etc. It's hard to change one without affecting the others.

All other things being equal - If you hold the CFM constant, and decrease the conduit diameter, you will increase the velocity of the flow. In theory this will occur via the inverse square relationship described before. I.E. cut the diameter in half, the velocity will increase by 4x. However, a smaller diameter pipe will also have more frictional loss per unit length. So the blower assembly that gave you, say 500 cfm with a 4" pipe would give less than 500 cfm with a 2" pipe.

The static pressure at the inlet to the pipe would be less for the smaller pipe than it would for the larger pipe, and would be greater at the dust collecter end of the pipe. This greater drop in pressure along the smaller pipe is due to the increased frictional losses, and it's this steeper pressure gradient that drives the flow faster.

Think of the analogy with the hose - Lets say you hook up a long hose and turn the spigot on half way. When you first release the hose, you'll get a lot of flow, because the pressure inside the full length of the hose will have equalized with the pressure in your indoor plumbing. That's the static pressure. After a while, though, the stream that you're seeing at the nozzle will decrease until you're left with a steady, weaker flow. That's the dynamic pressure. The full household pressure is available at the spigot in either case, but, while the water is flowing, it has to slide past the inside of the hose and negotiate lots of twists and turns on the way to the nozzle, so it loses a lot of its energy.

I guess I'm getting into this for a couple of reasons -
1. I'm an engineer, so I'm a complete and utter geek by my very nature

2. It's a balancing act. In my mind the Shopsmith DC has been designed to work well with the Shopsmith, and in my experience, it does. Other systems might work well, or might not - it would depend on the specific system in question - but it's not simply a case of the biggest HP number, or hose diameter, or CFM rating being the "best."

mickyd · Post by **mickyd** » Thu Apr 30, 2009 1:30 pm

guitarnut wrote:........... If I did the math correctly, each 12oz Miller Lite is 28.22 cu in of golden goodness!

Peace,
Mark
SW Indiana

Your off too much (+33%) on your Miller Lite answer.
12oz = 21.65625 cubic inches.

You must have been slamming down the 16 oz'er because 28.22 cu in = 15.6370563 US fluid ounces

Hey for those of you that don't know this already, google search does mathematical conversions for you. To check it out, just go to www.google.com and type in "12 fluid ounces into cubic inches" and hit enter. It will do ANY math conversion for you (even complex ones). Check it out.

guitarnut · Post by **guitarnut** » Thu Apr 30, 2009 2:00 pm

[quote="mickyd"]Your off too much (+33%) on your Miller Lite answer.
12oz = 21.65625 cubic inches.

You must have been slamming down the 16 oz'er because 28.22 cu in = 15.6370563 US fluid ounces

Ah, I was using the size of the can, not fluid ounces. Rookie mistake.

Peace,
Mark
SW Indiana

mickyd · Post by **mickyd** » Thu Apr 30, 2009 3:19 pm

guitarnut - Don't forget to fill out more of your personal profile. You only get 5 posts and if your location isn't filled in, the computer will kick you out!!!

guitarnut · Post by **guitarnut** » Thu Apr 30, 2009 3:24 pm

mickyd wrote:guitarnut - Don't forget to fill out more of your personal profile. You only get 5 posts and if your location isn't filled in, the computer will kick you out!!!

Got it. Thanks! I didn't know that would happen.

Peace,
Mark