Flowbench with a impeller anemometer

[Tiger331]

Hallo there,
I have build a flowbench with a impeller anemometer.
I have build in a prechamper and a bunch of straws to get the flow laminar. It works very fine and the display of the anemometer shows constant numbers. So I think, everything works fine.
The only "problem" is, that if the valves are closed, I read round about 25 cfm of flow at 28" of water?
Is this with all flowbenches or should I work on it to get it better?

thanks and regards
Hans

[Tiger331]

As there is no response for the question I will first give you some more informations about my flowbench.

I normally did really not need a flowbench, as I am not in business with this work, it is only for my own (home)work and I wanted to know if it is possible to build a flowbench with little money. And what should I say, it is possible (okay, with the help of ebay)

Here are some pictures:

[url=[URL=http://imageshack.us][/url]]Picture1[/URL]

[url=[URL=http://imageshack.us][/url]]Picture 2[/URL]

[url=[URL=http://imageshack.us][/url]]Picture 3[/URL]

As you can see, it is not professional build, but it works.

But I have one more question:

If I make a messuring and go up to 0,5" with my Trick Flow heads, the testing pressure with 28" water did not drop, when I go with the valvelift up to 0,55", it is climbing.
The cfm-rating is also climbing.
Normally, the testpressure must drop, when I open the valve more.
Did you make the same experiences or is there something wrong with my way to messure the testing pressure.

Thank you and regards
Hans

[bruce]

Looks good! Nothing wrong with a "not professional build" bench lots of them on this forum.

I think in order to answer some of your questions we need to know more about how/where you are taking your 28" pressure reading from? Where is your impeller located?

[Tony]

Nice looking bench there Tiger.

In fact, my very first flow experiments were with an anemometer (that I already had) and a leaf blower. The biggest problem was it would never give a steady constant repeatable reading. But it got me started.

[115-1172523331]

As the others have said, you have a nice looking bench. However, they didn't answer your original question about flow with the valves closed. To be flowing 25CFM, there has to be a leak (or number of leaks). Check your piping joints, the seams on the cabinet, and anywhere else air could get into the flow path without going through the head you are testing. Take the head off and seal that inlet, then start checking. Earlier posts have indicated that the wood will even let air THROUGH the box (if not sealed with epoxy, paint, or anything else to fill the pores). I think most of the benches you see here will be very close to zero flow. Good luck! We'll be looking forward to hearing the results! -- Doug

[Tiger331]

Thank you for the answers.

I will check this with the leak.

But my actually main-problem is the testing pressure with 28" whitch is not going down, when I open the valve from 0,5" to 0,55" and 0,6".
As the valve opens, the testing pressure must go down and therefore I must close the bypass to fix the pressure.
But not at this valveopenings.
Did you ever have the same experiences?

Thank you

Hans

p.s. sorry for my bad english, I work on it. But I hope you understand what I mean.

[bruce]

I would suspect a problem with your static pickup location?

Where is it located in your pictures?

[Tiger331]

I take the static compression in the prechamber.
There is a 8mm tube in the middle of the backwall whitch extends ca. 2" in the champer. The front of the tube is closed.
There are two holes with 3mm in the side of the tube. The holes show to the top and the bottom.

Is there something wrong with this?

I also lokate the tube in the corner of the prechamper, nothing changes.

regards
Hans

[WPH]

Quote:

"But I have one more question:

If I make a messuring and go up to 0,5" with my Trick Flow heads, the testing pressure with 28" water did not drop, when I go with the valvelift up to 0,55", it is climbing.
The cfm-rating is also climbing.
Normally, the testpressure must drop, when I open the valve more.
Did you make the same experiences or is there something wrong with my way to messure the testing pressure.

Thank you and regards
Hans"

Hans, check out the discussion on port velocities on this forum.
I think you may have an serious issue with turbulence @ 0.55" inches lift. Below that lift airflow isn't that turbulent
and your test pressure acts as it should. I've seen this on my own head when I was probing the port floor to find out
max. separation point in short side radius. Make a T-shaped probe of 1.5mm2 rigid copper wire and feed it along
the port floor closer and closer to SSR. Test at .500 lift and I think that you will see that test pressure goes up when
you reach the spot when the flow separates from the port floor.

I'm not shure if it works but it's easy to try.

[bruce]