Tractorsport Flowbench Forum Archive

Posted: **Mon Nov 27, 2006 7:21 am**

As a TOTAl new beginer to flow bench making and using, First let me say hi to every one on here.
second, were do you start???
I want to build my own flow bench, one: because I like doing this kind of thing, two: to keep costs down.
I am NOT a comercial user, I am a home car tuner/classic car restorer.
I have looked at many sites about flowbenches, I still dont know the basics of what it takes to make one.
I am Dyslexic, and find reading (more so taking in what I have read) a bit hard

In simple terms, can some one explain how to build one.
One more thing, as with most things, the first one you build, always gets developed, I dont want to make this mistake, buy building a to simple uint that will soon be not good enough.
NOR do I want to build the best unit that I can, and only use about half its use.
any help will go a long way.
many thanks
Piero

Posted: **Mon Nov 27, 2006 10:57 am**

At it's most basic, a flow bench is just a box with some blower motors, your head or what ever else might be testing sit on the box and the blowers make air flow through the head. Inside the box usually between the head and the blower is some means of measuring airflow and some way of controlling the amount of flow.

To measure the air flow, we most commonly use either an orifice of a pitot tube. An orifice provides a restriction to the airflow as a result, there's a pressure difference across the orifice by measuring this difference, we can calculate the airflow. Most commercially available flowbenchs use this method.

Pitot tubes are another measurement method popular with the members of these forums. A Pitot tube works by measuring the impact pressure of the air. Think of sticking your hand out of a moving car, the faster the car goes, the harder the air pushes against your hand. Pitot tubes provide a way of measuring the force of the moving air and from that the air velocity and volume can be calculated.

With either the orifice type of bench or the Pitot tube type, it's important to accurately measure the pressures generated and for this we use manometer, they are just fluid filled tubes and the amount of pressure applied moves and fluid and the amount of movement measures the pressure. Also, increasing common are electronic manometers.

What I found useful when I was trying to get my head around the principles of the flow bench was to study and thoroughly understand the math involved in the calculations. I would draw small diagrams of a flowbench, figure out where the pressure measurements needed to be made and by running through the math, I could understand how things needed to be sized etc.

Anyways, you've come to the right place to learn about these things, many of the people here are very experienced and willing to share their knowledge. Good Luck.

Posted: **Mon Nov 27, 2006 10:02 pm**

Rocco summed it up quite well...

If you're handy with home shop tools and can build a good, air tight cabinet..you've got half the battle down.

PM me with your email address and I'll send you the MSD bench articles in zip format. That will get you a good visual picture of an orifice bench and what's involved for material to build one.

As for the How It Works part.... should help clear up some more on this topic.

Remember to old saying....How do you eat an elephant?......one bite at a time!

Edited By larrycavan on 1164679597

Posted: **Mon Nov 27, 2006 10:06 pm**

Welcome! There is a lot of expertise here and reading previous posts or doing a word search is a good way to start. My bench is about as simple as can be, just a shelf with test opening, settling chamber below and a separate motor box on wheels. The two are connected together through various sizes of pitot flow tubes. Manometers are all homemade and screwed to the wall. All sorts of spreadsheets are available here for calculating the actual flow, no matter the style of bench. There are prepackaged electronic flow devices, Flow Performance for one, that are almost stand alone, and can use almost any power source, even a shop vacuum. This will also require some sort of computer to provide the readout, and even a Palm type PC will work. You will find this endeavor very interesting.

Posted: **Tue Nov 28, 2006 6:15 am**

Thanks guys :;):
I have done searches on web, found many sites.
A few things concern me.
1: does the sucking force affect the readings??
2:does the tube size and lenght affect the reading??
3; does the liquide dencity and amount in manometer affect reading??
4:how do you make sure that the cfm figuers are standard.
many thanks guys

Posted: **Tue Nov 28, 2006 11:11 pm**

I can't speak for an orifice style bench, but essentially everything does affect everything else.

1. The power of the air moving system will certainly have an effect. It sounds like you are talking about a pitot system, and you need to have somewhat substantial air speed through the measuring instrument to get a good reading on a conventional manometer. Electronic measuring instruments seem to have a wider confident operating range for any given size tube or orifice.
2. The tube internal area for a pitot is a basic unit used for calculating air flow. The tube needs to be long enough for smooth air flow, before and after the sensor. There are basic figures for the minimum length, such as 10 diameters ahead of the sensor and 5 downstraem. These are not hard numbers, but an example. Flow straightening devices can help in this regard by allowing a shorter overall length. Longer lengths will increase friction loss through the pipe, and isn't really harmful but it does require more power to pull or push the air through a longer length. Not really noticeable on a 3" but smaller diameters, such as 2" will show up more.
3. The density of the measuring fluid will affect the scale for the manometer. The standard we use is water. If the fluid density is more or less, the scale must be adjusted or interpreted to the water standard. Not really difficult. I used Marvel Mystery Oil, s.g. of .83, for the fluid on some manometers and it works pretty well and doesn't freeze. The scale is expanded to match the lower density. I did switch back to water for faster response though. A U-tube manometer doesn't matter how much fluid is inside, the fluid will automatically equalize on both legs of the U. An inclined meter is generally a well type manometer with a large reservoir at the low end and the fluid is pushed or pulled from the well up inclined tube for the reading. The reservoir should be as large as possible within space constraints since you don't measure the drop in the reservior to add to the rise in the inclined tube. Mine are 500:1 ratio, and larger is better. I added that ratio of drop to my spreadsheet for the inclined reading but it is of little effect.
4. The most common way to test or calibrate the bench is to flow it against a known standard. Bruce makes nice orifice plates for testing your bench. While it is good to have confidence the actual reading is absolutely correct, it is probably more important to get repeatable results.

Posted: **Wed Nov 29, 2006 4:40 am**

Thanks 4 that.
sort of followed most of it, it will all make sence, the more I learn, but thats just it, need to learn more ???
I dont know as yet which type flowbench I want to build, I dont have a preferance, not realy understanding the differance from one to the other.
All I realy want is a simple ish, comon flowbench that I can conpair my reading with other flowbench use'ers.
thats why I asked if there was a standard.
One question that springs to mind, is there a lot of calculating to do with the figers a flowbench gives????
Does the electronic type, as in (Micro Flow Bench) do it all for you (maths)
last question, is there a diagrame any were on the net of a flowbench (i seem to follow diagrames a LOT more easyer)
many thanks

Posted: **Wed Nov 29, 2006 10:45 pm**

There is lots of information about all of the aspects of flow bench types and construction on this site and others Lots of photos and diagrams of project benches made by the users of this site. The information you seek is all here. Regarding the use of electronics, I have no direct experience with digital flowbenching, but it certainly gives the choice of the type of readout desired, velocity or actual flow. Essentially it does the calculating required in real time, making the process faster, although not necessarily more accurate.

Posted: **Thu Nov 30, 2006 9:06 pm**

The two types of benches are both well supported here. Just pick one type and give a holler when you have a question. Someone will come to your aid.

An orifice bench functions by measuring 2 different pressure differentials. To measure the actual flow, the pressure differential that is created as air passes through an orifice is measured by the inclinde manometer. That pressure is then converted into CFM.

A pitot bench measures velocity through a pipe. That velocity is then converted to CFM.

Both types of benches use area values to arrive at the CFM value.

Both types of benches also use a test pressure manometer that measures the pressure differential between the atmosphere and a section of the flow path. That is your constant. It is how your arrive at the same standard of testing each time.

An inclined manometer, U Tube manometer and manometer with a reservoir [rather than a U Tube] all function in exactly the same way. Pressure applied on one end caused he fluid level to change. That change is measured in inches of water column.

I highly suggest looking over Dwyer Instruments web site and also doing a search for manometer function on Google.

Posted: **Mon Dec 11, 2006 11:27 pm**

I'm new as well. I have seen plans for both types of bench. We do Harley Davidson heads can you give me some sugestions on which would work better and is there some way to simulate the effect of the piston position in the cylinder as well as valve opening
thank you
John

Posted: **Tue Dec 12, 2006 10:35 am**

I think that either style of bench will work fine when working with Harley heads. I have a Superflow 110 which is a benchtop orifice style bench. It's not particularly powerful but it works good. The Harley heads that I've done improved greatly with some porting and valve job work especially the intake. I just used a cylinder jug as a fixture for testing the cylinder head.

I don't know of a way to simulate the position of the piston in a four stroke application to see how it effects flow at low valve lifts, that's something I always wanted to try.

Posted: **Tue Dec 12, 2006 7:36 pm**

We had good results on evo heads just cleaning up the ports and dome. But Twin cam heads are a different story. There are a lot of guys makeing big port heads that have great flow bench numbers and they dont work as well on the bike. I have got some ideas on what might work but im not sure how to prove them out I have never had a lot of fath in dynos and there hard on air cooled engines.
John

Posted: **Mon Jan 01, 2007 2:20 am**

Hey where is every body I can't sleep, keep thinking about this Flow Bench, Watched The Ball drop at midnight and it made me think of a golf ball! and that turned into dimples on the SSR, So of course I had to see what was going on in the world of Flow Benches. :laugh: My wife say's I have Issues!

Happy New year

Rick

Tractorsport Flowbench Forum Archive

Were do you start!!!