PTS Flowbench Forum

1960FL wrote:Flowghost,

You say you have a 200 CFM plate at what preasure" 16" ro 28" this could work fine to calibrate.

If it is a 200CFM at 16" DP it will flow 264.8CFM at 28 and .62CD Just call it 265CFM Try to calibrate to this and use it streight on the bench deck without a head adapter sharp edge up on intake mode.

Rick

It's 200cfm at 28" Rick. I'm going to work on it tomorrow and see where I end up.

What plate are you using inside the bench?

That plate needs to be rated for 16"

Okay, I did some more messing with this thing. Since I don't know what I'm doing yet, maybe you folks can make sense of what I need to do. Here are some of the software #s:

Density - .072
Density Water - 62.28
Orifice Diameter - 3"
GC - 32.2
Discharge Coefficient - .62

I slapped the 200cfm@28" plate on top with the 300cfm@28" plate inside. It appears from what I have read that I need a 300@16" plate inside, but here's what I got anyway:

@200cfm:
Depression - 18.0
H20 - 17.9-18.0"

Full power:
Dep - 31.6
CFM - 271
H20 - 31.5

Set at 28" H20:
Dep. - 28.7
CFM - 251
H20 - 28.3

All advice would be appreciated.

The 300@28" plate is rated 226@16" so the max you could read would be around 200@28". It's diameter is 2.045" so I'm not sure where you got 3" for FlowSoft Configuration? Having 3" in your configuration is giving you those high numbers.

You need an internal plate that is rated for 16" and is 25-50 cfm higher than the max CFM you plan on testing.

All advice would be appreciated. ?

Flowghost,

Ok, I would recommend a couple of things, one go back to the index page of the forum and read the Flowbench 101 doc and make sure you truly understand what exactly Delta P is. Your problems are that you do not really understand how this design flowbench works and what exactly the differential pressures or test depression are and how they affect the final flow numbers. Please do not take me wrong here I am just responding to what you have said in prior posts and want to help with the light bulb coming on.

The most important numbers in the bench are internal plate specifications and the Delta P (differential pressure across the internal orifice). The depression is just a standard of which we test to as you will see it could be 10”, 28”, 36”, 40” and the flow readings of one can be mathematically transposed to the other ( in FlowSoft this is “Comparative Flow”). Example your bench can only pull 25” at its max flow but you want to know what it equals at 28” this is done mathematically the formula is posted on the forum for you to better understand. Note this is the information you see in test sheets or advertisements head flows 250CFM at 28” etc.

So it does not matter what test pressure you are testing at as long as the part you are testing cannot flow more than the internal orifice can at its rated depression. Example to calibrate a 200CFM plate rated at 28” on the top of the bench you need to have a minimum 250CFM at 16” plate inside the bench. The digital Monometer is designed to work with only a plate rates at 16” inside the bench!
Why? In simple terms if the hole inside the bench is smaller than the one being tested you will never flow enough air through it to create the test depression! So the bench internal plate will reach max DP before you can get to your test depression. This is a good way to damage the Digital monometer, those that use fluid monometers at his point would blow the fluid out of the incline!. (see flowbench 101 schematic)

Last I recommend you download Ed’s (86Rocco) spread sheet and just play with it changing the orifice diameter and pressure differential to see how they affect the flow in CFM. This will help you better understand orifice plates and where the numbers come from. Caution do not try to use this sheet to make your own plates until you truly understand the above and just what the CD (Coefficient of Discharge) is and it effect on flow.

http://www.flowbenchtech.com/forum/down ... php?id=167

I hope this helps.

Rick

Brucepts wrote:The 300@28" plate is rated 226@16" so the max you could read would be around 200@28". It's diameter is 2.045" so I'm not sure where you got 3" for FlowSoft Configuration? Having 3" in your configuration is giving you those high numbers.

You need an internal plate that is rated for 16" and is 25-50 cfm higher than the max CFM you plan on testing.

Okay, I have read the 101. It's a little clearer to me (although not entirely). If I am going to do heads that breathe up to 300cfm@28" my orifice plate should be at least 350cfm@16" correct? I can then use the 200cfm@28" or the 300cfm@28" to calibrate the bench? If I was then to slap a head on the bench and measure would I have to adjust to 28" for each increment of valve lift .01",.02",.03"... to get correct numbers?

Yes, you have it correct

28" becomes your standard to test to so you have to reset your bench to 28" for each test point. It could actually be any number you decide ie 10", 25" etc

Brucepts wrote:Yes, you have it correct

28" becomes your standard to test to so you have to reset your bench to 28" for each test point. It could actually be any number you decide ie 10", 25" etc

Okay, so if I choose to test at 10" to keep from burning out my motors, then I can plug the numbers into the formula to calculate for 28"? I'll order the 16" plate today.

Okay, I installed the 300cfm@16" in the bench. When I put the 200cfm@28" plate on the bench I get 165cfm@28".

Did you change the plate diameter in FlowSoft?

Did you adjust the Cd in FlowSoft till that plate reads 200cfm @28"?