Tractorsport Flowbench Forum Archive

Posted: **Sun Aug 17, 2008 10:10 am**

Im thinking about building an orfice bench.
How do i calculate the sizing form orfice plates and how do i calibrate the inclinded monometer.
Is there a formula for the sizing of a sharp edge orfice?
Imnot real good at posting but larry told me no such thing as a stupid question and there are so many nice people here to help
Thank you
Randy

Posted: **Sun Aug 17, 2008 10:16 am**

Follow this link over to the spreadsheet area of the forum:

Posted: **Sun Aug 17, 2008 10:17 am**

Randy;

First off do a search on the Formulas section to see al the work others have put into helping us all.. You can find the sheet you need here.

Rick

Guess Bruce pushed go first ;-)

Posted: **Sun Aug 17, 2008 10:34 am**

I pinned that topic now in the Spreadsheet area.

It can be a pain to find some of the old posts!

Posted: **Sun Aug 17, 2008 10:38 am**

Randy, there are two spreadsheets in that post, you'll probably find the second one more useful.

Posted: **Mon Oct 06, 2008 6:31 pm**

I found these two online orifice calculators to be very useful

The first one requires you to download Java freeware

The other is used for determining orifice hole diameter

Enjoy
Jim

Posted: **Mon Oct 27, 2008 6:19 am**

Posted: **Mon Oct 27, 2008 6:40 am**

The link to a spreadsheet was posted above. I use my own spreadsheet that I wrote for my orifice plate design/machining, you'll have to understand that I'm not willing to share my spreadsheet (I do have to keep some "secrets"). Ed's sheet in the above post/link will get you what you need as well as the links posted by Gannet.

Posted: **Mon Oct 27, 2008 12:41 pm**

Posted: **Mon Oct 27, 2008 3:06 pm**

Thanks Tony for the excellent explanation . . . sometimes I "assume" everyone who is here on the forum understands. I have to remember we are all still learning.

Posted: **Mon Oct 27, 2008 6:11 pm**

Posted: **Mon Oct 27, 2008 6:58 pm**

I would not worry too much at this stage about an exact discharge coefficient. Just try to figure out roughly what sort of design pressure drop you plan to have and, initially make yourself some home made orifice plates from the figures here at the Forum. Get the bench up and running, leak test it, and sort out any problems.

Only at that stage do you really need something serious to calibrate against.

Many people here have built benches from scratch with no outside help at all, and when finally checked against a standard reference orifice they were within a very few percent.

There are several very accurate ways to measure flow other than with an orifice. You can check an orifice against another flow standard and work backwards to calculate the discharge coefficient.

One such method is to use a floating gas bell. Just like the old gasometers. A large cylindrical inverted bucket floats in a large and deep tank of water. You feed air in, it rises, you allow air to escape it sinks lower in the tank. The internal volume can be very accurately measured, so by measuring the distance the gas bell rises or falls you know exactly the volume of air in cubic feet entering or leaving. This is ideal, because it works at constant pressure. The weight of the gas bell determines the pressure, but it is usually quite low.

We had a system exactly like this at a national standards laboratory I once worked at. It was a primary flow standard against which other things were calibrated. Unfortunately the entire laboratory was shifted interstate a few years ago, so I no longer have access to it.

Posted: **Mon Oct 27, 2008 7:46 pm**

Posted: **Mon Oct 27, 2008 10:48 pm**

Posted: **Sat Nov 08, 2008 10:47 pm**

I have my bench built and the vacuum motors are on the way, now I would like to purchase an orfice plate but I have no idea of which one to get, can someone point me in the right direction?
Thanks guys.

Tractorsport Flowbench Forum Archive

building an orfice bench - orfice lates and inclined manometers