Completly understanding flow benches - How to build a flow bench?

[jofelt78]

I need some real help. I am currently building some small ohv go-kart engines. In the past, they have been basically stock w/ stock componants. They have now opened up the rules to allow porting, carb. work etc.. I currently own a machine shop. I want to build my own small comparison flow bench. I can fabricate and machine all of my own parts, but I simply don't understand how flow benches work. I have read alot, and looked at alot of pics, but I dont truly understand how to build the right one. I know there are different types :pitot tube, setting chamber etc... Which is right for me? What size pvc to use? How long of pvc to route from plate to motors? How the pitot tubes work? What is the difference of the inclined maometer to the vertical manometer? How many manometers to use? Where do I place the pitot tubes? Are there dimentions to follow to place the pitot tubes in the right place? I'm sure you get it by now. I need everything. I know this is asking alot, but I am desperate. I really want to understand how to build it and build it right. Thanks

[bruce]

All the info you seek is already in various posts all over this forum. By readings the past posts you should end up having a good working knowledge of what will work for your application.

A few questions to ask yourself;

1. What do I plan on testing ie sizes of ports, carb bore diameters? (this will determine the vacuum source you need)

2. What level of accuracy will I be comfortable with? (determines the price range and what kinda of water manometers or digital you will need) Personally after having the opportunity to use a digital setup I'd never go back to water gages.

3. How much space do you have in your shop for a bench? My bench is very compact and has excellent repeatability with short runs of PVC using annubar/pitot, my bench is around 40" in length.

You are going to find a varied opinion on this subject from the members here. I prefer the pitot style of bench others prefer the orifice.

Oh, one more thing welcome to the forum!



Edited By bruce on 1104765769

[86rocco]

Well, here's a few basics: there are two commonly used types of flow benches, pitot tube and orifice type. Both types have powerful blowers which force air through your test piece and a means to throttle the flow either by controling the speed of the blowers, a valve to restrict the air flow or bleed off some of the flow, the point of this is to be able to accurately adjust the pressure difference across your test piece.

Here's a pretty good primer on pitot tubes. Basically a pitot measures the dynamic pressure of moving air, the higher the speed of the air the higher the pressure. By measuring this pressure, the velocity of the air can be calculated and from that the flow volume through a given sized pipe. With a pitot tube, it's important to measure the pressure at a point with is representative of the system as a whole so, long straight pipes are used to straighten the flow and reduce turbulance to a minimum and the pitot tube is placed more or less in the middle.

An orifice flow bench uses a different method measure the air flow, a restriction (i.e. an orifice) is placed in the air flow and the pressure difference across the restriction is related to the amount of air flowing through it and for an orifice the relationship between pressure difference and flow is governed by a well known mathematical formula. The settling chambers and plenums in the flow bench are there so that the flow through the orifice matches as closely as possible that of the "ideal" orifice assumed by the mathematical formulae.

Both types of benches use two manometers, one usually vertical, is used to measure the pressure difference across your test piece, this pressure is often refered to as the depression, typically the depression is adjusted to one specific value for all tests, 10" h2o and 28" h2o are 2 of the more common test pressures used. The other manometer usually inclined, is used to measure the actual flow either by the pitot tube method or the orifice method. The manometer is inclined only because these pressures are typically fairly low and having the manometer inclined makes it easier to measure small differences.

BTW, there is one more type of flow bench, a laminar flow type, this is used on some high end commercial benches but not common for shop-built benches so for the purposes of this discussion, I've ignored it.

[DaveMcLain]

I would say that you will need a bench with flow capabilities along the lines of a Superflow 60 or 110. I've got a 110 that I use all the time, it produces fast accurate and repeatable results. I bought it a few years ago and it's been great, at that time the Audie Flow Quick and Perf Trends EZ flow were not on the market. I've got a friend who's building a bench using the EZ Flow because it uses the same software that I use on my Superflow bench. I've got a friend who has an Audie Flow Quick and it produces very comparable results to my Superflow....

[jofelt78]

Thanks alot guys. I am getting a better understanding of all this. Like I said before, I really want to do this right. I believe I want a pitot style bench. Now here is what I have to work with:

1. Space is not a problem, but mabye 3' or 4' square?

2. I have 3 manometers:
2 TPI 615 models (single input
pressure diff. meter)
1 TPI 645 model (dual input pressure diff meters)
(Father in-law is a tool rep... he treats me good.)

3. Carbs. are 1.040 dia. / Intake manifold is 2" long/ Head is approx. 3" long/ Valves are 1.080 dia.
(this is all I plan on flowing on this machine)

Now I get the basic idea of everything.... I think lol

Would anyone draw a detail scematic of what I need (sizes and dimentions) or send lots of pics either on here or by e-mail. Remember I am a novice so any details are greatly appreciated. Thanks again for any one who has taken time to help.

jofelt78@sbcglobal.net

[fchp]

Here is a link to my bench I built just for doing karting engines. By changing the adapter plate on the top I can do flathead or OHV engines. I can do carbs & intakes alone or flow through the head. With a single motor in our engine sizes I can flow up to 48" if required, but generally do all my testing at 28".


And I would say I found about 99% of the info required in building it right here on this forum. The other 1% was through emails from this forum or general internet searches.

[highoctane110]

I am intrested in building a flowbench, for mainly garden pulling tractors. I have been doing my reserch and I would like to go all digital. Now I have a dyno with the performance trends software so I am kind of thinking in that direction, but I would like to know what everyone else thinks? The setup that I am thinking about is the quick flow but I also want the pitot tube for air speed. If anybody knows of any thing better it would be greatly appreciated. I am definitly not for spending the long dollar for a name.
Shane

[Tom Vaught]

I will not say that I do not admire Mr Neal Chance for coming up
with the first Super Flow bench when he too could not afford the
"High Dollar" benches that were out there at the time.

At that time only the large OEMs and a few other shops had a flow bench.

He built that need into a multi million dollar company.

Unfortunately he is now the big money guy and the people on the board are trying to save money and build good inexpensive benches like the first one he built too.

There is a vast wealth of knowledge on this forum. Go through
the posts and the posts from the previous forums if you want to
understand the whole theory deal. If not just copy a bench like
several of the ones in this forum and use your time to go racing!

Welcome to the board.

Tom V.