flowbench design - floaing depression

[302ford]

Has anyone ever concidered flowing with a floating depression. A typical engine can pull 120 inches of depression an the valve opens and goes down from there.Wouldnt this more simulate the conditions of a engine running condition than the standard 28 inches of depression.
Just an opion

[thomasvaught-1]

We simulate that condition somewhat at Ford when we measure the same head at 10", 20.4" 25" 28" 40" and 67" of test pressure. We also have our Mass Air Meter and Pressure sensors: (map and bap) to help us plot vehicle conditions.

Tom V.

[86rocco1]

As a practical matter, it should also be noted that a flowbench capable of a few hundred cfm with 120" depression would require an enormous amount of power to run.

On a most theoretical level, due to the dynamic nature of a running engine and the static nature of a flowbench, flowbenchs are by their very nature a compromise between what we want to test and what we're able to test, depression is just one of the components of that compromise.

[Tony]

Agree with the others here. Test at a fixed depression, or several fixed depressions to get accurate repeatable flow and velocity numbers.

The conditions within a running engine can never be fully duplicated on a flow bench, because of thermal effects as much as just the pressure/flow effects.

A dynamometer is the way to finally test your handiwork.

The actual mechanical drive horsepower required to flow air against considerable back pressure may surprise you. Most of us are limited by the total electrical power available as to maximum achievable flow and test pressures in our benches.

[302ford]

I am in the process of building a low cost bench using a shop vac. as the vac source and using the floating depression method. If any one is interested let me know and ill expalin my theory. Later if this works out going to build a setting box with 4 or so vac motors for more pulling capacity.

[thomasvaught-1]

I would be interested in your theory.

Tom Vaught

[bruce]

I agree . . . the floor is all your's, we're listening



Edited By bruce on 1214060113

[Tony]

302Ford, I assume you are referring to this thread by Dave Vizard on the Go Faster Forum ?



While it is an interesting idea, to make it work, and be repeatable, requires an exact known flow versus depression curve for your air blower.

It then assumes nothing will ever change. But what if the mains supply voltage varies, or the blower motors heat up, or the weather changes ? That will change the shape of the pressure versus flow curve of the blower.

I believe that the biggest problem with this idea will be the rather poor repeatability.
And repeatability is absolutely the most vitally important feature of any flow bench.

A much better approach, is to flow the the SAME AIR first through the test piece, and then through a fixed known measurement orifice.
The ratiometric relationship between the two easily measured pressure drops will remain constant, regardless of any changes to the actual air quantity or quality.

That is the beauty and simplicity of the traditional orifice flow bench.
It completely eliminates a number of inconvenient variables and correction factors, by flowing the exact same air through two restrictions in series. One of which is a known reference restriction.

[thomasvaught-1]

Quote:

"Although unconfirmed I have heard that Fords flow bench can approach real world pressure drops and that it cost a mere seven figure number to build"

Interesting! 27.7" H20 = 1 psi so 120 psi =
3,324 INCHES OF WATER TEST PRESSURE!

May be a bit of stretch for our 7 figure flow bench you guys are familar with, lol!

The 7 figure deal is correct though.

That being said, I have investigated using high pressure air flowing through a test part and then flowing through an orifice. You need some very good (FAST) instrumentation and data-logging to take the readings.

Tom V.

[bruce]

This process only seems to be discussed on one forum (GFN) on the net?

Wonder why that is?

[Maxflow]

[Tony]

Just be aware that controlling the motor supply voltage most certainly does not positively fix the blower motor operating parameters.

In this type of series wound motor, the speed and torque are both notoriously variable, and available motor power is influenced by the temperature and the electrical resistance of the windings.

Unfortunately pressure rises roughly to the square of motor rpm, and the temperature of the windings will vary with the mass of cooling airflow. There is far more going on than just assuming that a corrected mains voltage will guarantee absolutely repeatable motor and blower characteristics.

If you have to do it this way, a blower tachometer might be an interesting aid to repeatability. I believe you would have extreme difficulty holding the required steady rpm with these types of blower motors, and that should tell you something.

[106-1194218389]

After reading the posts in this thread it just seems to me that the easiest way to go is just build an orifice bench. JMO I really like mine compared to the other 2 ways I was flowing. It seemed like I was always doing something to get them to repeat but after I built this orifice bench I can go back and reflow a known head and be super close to what it was even months later.

John

[Sir Yun]

Hi Bruce and y'all

one could use floating depresssion on an orifice bench (in addition to standard pressure drop).

[bruce]

One question . . . why?

In rebuttal . . . why induce possibly another way to add error into your readings? If you want to test at various flow depressions, then test at various test depressions and compare apples to apples. You build a tool to test something and then rely on conversion math to give you the readings? Yes, the math might agree but again back to the error thing, what if it doesn't and you don't know it doesn't?

Setting the flow depression and "seeing" it gives me a warm fuzzy feeling that I know it's correct.