PTS Flowbench Forum

I'm trying to calculate orifice plate size but I don't know which pressure drop to use !?
Could someone tell me the idea of this pressure drop?

I'm sorry because of my bad English, I hope you are able to understand me...
-Matias

The pressure drop across the orifice plate is a measure of the airflow. When sizing the orifice, there are two things to consider, the maximum range of your manometer and the maximum amount of air you expect to flow.

Have a look at the spreadsheet in THIS THREAD, one of the sheets there is called "Orifice Flow and Size", pay around with the numbers a bit, see what happens and pretty quickly, you'll get a handle on the problem. BTW, the numbers in black are the parameters you can change, the numbers in blue are constants or calculated values.

My system will consist of two vacuum motors (both are two stage motors). For a start I'm using Performance Trends "Black Box" and "Port Flow Analyzer Pro" -software. Black Box is basically just an electrical manometer and with the software I'm able to set the max reading of the manometer, so in this case I could use what ever pressure drop across the orifice plate when calculating the size of the orifice plate. But should I use as small pressure drop (across the orifice plate) as possible because I have just two vacuum motors?

Ps. I'd like to be able to use 28" test pressure, am I just dreaming?!

MatiasAho2 wrote:My system will consist of two vacuum motors (both are two stage motors). For a start I'm using Performance Trends "Black Box" and "Port Flow Analyzer Pro" -software. Black Box is basically just an electrical manometer and with the software I'm able to set the max reading of the manometer, so in this case I could use what ever pressure drop across the orifice plate when calculating the size of the orifice plate. But should I use as small pressure drop (across the orifice plate) as possible because I have just two vacuum motors?

Ps. I'd like to be able to use 28" test pressure, am I just dreaming?!

I am using the Performance Trends Black Box and PFA Pro software. I am just using 2 shops vacuums, big ones, 6.5 hp Craftsman and a 4.5 hp Craftsman, and I can pull 10" through a Small Block Chev Head that is flowing 263 cfm at 28". If you have big motors I would guess you could get 12". I would like to know so keep us informed.

I am trying to get an 8 motor bench built and have all the parts, just no time.

John

OK, now it seems that I'm going to be able to use 10-12" test pressure. I still don't know what pressure drop i should use when calculating the size of the orifice plate...

Did you ask PT what he (Kevin) recommends to use with their digital product?

He is going to know what would be the best pressure to work with the sensors that are used in his Black Box.

If it uses a 40" sensor and you use 10" you are only using 25% of that sensors scale which cuts down on the resolution of your scale. It also puts the readings into the lower end of the sensor's range.

As a comparison my DM uses a 16" sensor and we use a 16" DP (100% of scale) so our resolution is smaller.

I mentioned earlier that I have the Black Box and the Port Flow Analyzer Pro software. There is a manual on the CD or you can down load it from the PT web site. There is a calibration process you should follow. It walks you through a calibration process that matches your water gauges if you have them. I have my Delta p set at 12".

Here is a note from PT website "For Flow Bench Testing, the standard $519 Black Box II MPX comes with two 1.45 psi (40" water) sensors and a swirl meter input." The Black Box I have has 5 lb sensors or 120" H2O sensors. The more expensive Black Box I think has the 120" sensors in it. My Black Box is an early one and has (3) 5 lb sensors in it. Mine works great at 12", that is the Black Box though and may be a different ball game than Bruce's DM. Please be sure to read how to calibrate the Black Box. Print the manual out if needed and follow that. Have Bruce make you a calibration orifice and have him tell you what it flows at 10" of 12" and calibrate your bench to that.

John

Thank you Bruce, John and rocco. Now I think that I have a better picture of how to make the orifice plate.

Came across this in my reading research. (tom c)

http://okcc.com/PDF/Fundamentals%20of%2 ... 0pg.45.pdf

Now this thing came to my mind:

When I have just two vacuum motors should I use as small presure drop accross the orifice plate as possible to make max test pressure bigger?!

I'm thinking it that way that vacuum motor is able to produce the pressure drop "X", so

X - pressure drop accross the orifice = max test pressure

? ?