How do i calculate CFM?

[UKDoug]

[color=#000000]First of all Hi. My names Doug from the UK.

I

[bruce]

[quote="UKDoug"][color=#000000]For the sake of fifty bucks (see I can talk American!) I will probably buy a set of Bruce

[UKDoug]

Is that the spreadsheet by ED??

Bruce, could you help me with the calculating CFM question?

Thanks,

Doug.

[86rocco1]

Here's a schematic of a very simple orifice type flow bench. It works by taking advantage of the fact that if we have a careful calibrated orifice, the air flow through it is very predictable and can be easily calculated (see for details about that). Now since all of the air that goes through a test piece like your manifold for example, also goes through the orifice and since we can calculate the air flow through the orifice we therefore know how much air is flowing through the test piece. A fixed test pressure or depression isn't really necessary but it's normally used because it makes meaningful comparisons much easier.



Cheers
Ed

[UKDoug]

Thanks Ed. That makes sense. Looks like I had my manometers the wrong way round to.

I'm going to do a bit more Reading and will probably come back with a whole bunch of new questions tomorrow.

Either of you any idea on my question about sizing the vacuum source?

Thanks,

Doug.

[bruce]

Vacuum sources are very subjective to the blower design so a simple answer is not always possible.

Tony would be the resident blower person along with a few others he/they will come along and offer up an opinion . . .

[UKDoug]

I guess the way for me to move forward is to build a simple two chamber box with some quick home made orrifice plates and test my vacuum source.

I'm going to try using the vacuum motors stripped out of three 2000w vacuum cleaners. 6kw or 8hp total.


I've been going through the test process to get it right in my head. Please correct me if i'm going wrong.

1)Select appropriate orrifice plate for scale. Dependant on vacuum source and max flow of part being measured.

2)Orrifice plate must have larger cross sectional area than part being measured???

3)With no part on bench set vacuum to 10" 28" or other on vertical manometer.

4)Fit part and use inclined manometer to read pressure difference across orifice plate.

5) Use Ed's spreadsheet to set up inclined manometer. Using a known flow orrifice plate you use the % figure in the first coloum of Ed's spreadsheet to work out CFM??

Is that about right???

Thanks,

Doug.

[thomasvaught-1]

You might not have your manometer plumbed backward. Ed's simple drawing is not exactly 100% correct. He needs to show the reservoir location and the "at rest" fluid height. Assuming a few things with Ed's drawing would imply that the fluid on the left side of the Inclined manometer would be decending towards the right side of the manometer as pressure went up in the upper chamber vs the lower chamber. Without the vertical leg (well) of the inclined manometer, as soon as you fired up the bench any fluid would immediately be sucked into the bench if not already emptied by gravity alone. Simple corrections but confusing if you do not understand the actual systems (manometers) in operation. If we do drawings, we need to be very accurate on the actual design (pics/drawings) of the parts or confusion will immediately occur.

Tom Vaught

[86rocco1]

Sorry about that Tom, my drawing was never intended to be an exact representation of a working flowbench rather the intent was merely to show the relative layout of the salient items, I should have included a caveat to that effect.

[thomasvaught-1]

No "Rocks", Ed. Just did not want someone to drain a bunch of water in their bench trying to make the manometers work.

Hope you had a great Holiday and have a great 2009.

Tom Vaught